From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31E422E8DEC for ; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; cv=none; b=hD+zj7k01jNHVbkxicPXcWgQKoPpz7+WS+ziBhA8Xo4CKv7FnQ72l9Mps3duUH8IdwjwL6htBJmA7xoH+FWSR7TbO5mpP3LpQKUhA6mTmyTwah/BPjI+T3RTrlp9ei2Fy6GdvG2J5Sq6woVqwg7DnfIELT0KaFjDqV6ChgzWxok= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; c=relaxed/simple; bh=ejHgdDAabKDPyZoSRHRPybzahuBisuPz+K6hBpo1uWI=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=nSTJDE6t3f7yqAUg3nLywK4039I3AuSlZFQG4DGj8hhG684a9PyH9Qy9dP+L1u9XIFEM/V98PnBgzdspStRwM+zVAuXH/L8fixAZzzyo7NZGaJZsTMeRE3/aRB0JsZPLckW6o91bN4TroevbSwMxsMeAX14SGbkt52177Ng32xI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m0961o/9; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="m0961o/9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E3917C2BC86; Tue, 10 Mar 2026 14:35:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153352; bh=ejHgdDAabKDPyZoSRHRPybzahuBisuPz+K6hBpo1uWI=; h=Date:From:To:Cc:Subject:References:From; b=m0961o/9TmU2a4NUKKSkrYCCYeYIjgU+RCsK9lbLXr2dmtlhTmx0vBhxiaJhKsxvj 3H2gB0IqObMoJDsixdkoDUbnKZipQDtRUINR9JXQd5feqhEFFnaYMnn6Dlv46Ru0mY JYQ301Nz9B3A8U45CqE1FBsM4xvnqVEeVsMZ1jyqVeD6sEj9mKkk7KaWtV4qsUqLKb 7tk88Uc88rRQm5cGUEuzy5EHRhTXpmNoA79DbMKBRln5VDTuCQ2y4XfAL7xvnRDa3E f6Gf5XIjsH9yMedtz7YxpE5bkdZiqaHfmYYCSBw2jYQz6FS1c5Nbf7qeFiARtbI0Lx F+VNBXM+Bc9uw== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBm-00000002ZZr-3k3x; Tue, 10 Mar 2026 10:36:02 -0400 Message-ID: <20260310143602.750104863@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:16 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 01/18] ring-buffer: Add page statistics to the meta-page References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Add two fields pages_touched and pages_lost to the ring-buffer meta-page. Those fields are useful to get the number of used pages in the ring-buffer. Link: https://patch.msgid.link/20260309162516.2623589-2-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/uapi/linux/trace_mmap.h | 8 ++++---- kernel/trace/ring_buffer.c | 2 ++ 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mma= p.h index c102ef35d11e..e8185889a1c8 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -17,8 +17,8 @@ * @entries: Number of entries in the ring-buffer. * @overrun: Number of entries lost in the ring-buffer. * @read: Number of entries that have been read. - * @Reserved1: Internal use only. - * @Reserved2: Internal use only. + * @pages_lost: Number of pages overwritten by the writer. + * @pages_touched: Number of pages written by the writer. */ struct trace_buffer_meta { __u32 meta_page_size; @@ -39,8 +39,8 @@ struct trace_buffer_meta { __u64 overrun; __u64 read; =20 - __u64 Reserved1; - __u64 Reserved2; + __u64 pages_lost; + __u64 pages_touched; }; =20 #define TRACE_MMAP_IOCTL_GET_READER _IO('R', 0x20) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 17d0ea0cc3e6..82b4df579670 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6154,6 +6154,8 @@ static void rb_update_meta_page(struct ring_buffer_pe= r_cpu *cpu_buffer) meta->entries =3D local_read(&cpu_buffer->entries); meta->overrun =3D local_read(&cpu_buffer->overrun); meta->read =3D cpu_buffer->read; + meta->pages_lost =3D local_read(&cpu_buffer->pages_lost); + meta->pages_touched =3D local_read(&cpu_buffer->pages_touched); =20 /* Some archs do not have data cache coherency between kernel and user-sp= ace */ flush_kernel_vmap_range(cpu_buffer->meta_page, PAGE_SIZE); --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31DDE2E88BD for ; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; cv=none; b=JUEkWUtruNlQchTC72AjiQFzpKYrD0chK7qeFnIrqszGUjeA0cLTPn1GUMFayLCcAs7pOXzTIWWRYdnNN1e+++1gOS41HA5jUCTJOjn9RZW/ZJwbPxpfbFJOL8YTqSrUhhYKsuTNoIA25qQuBs6Za7L2r9zBnJqE7Skq6ci3DFE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; c=relaxed/simple; bh=NNr9V78uXJ/VI+bEPvEAkQ8ULjTN/7EWompKerAAGzs=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=n2h4Zv3Vif4tKxdgTSFN5dK1EvdykwDB73N9clLOa6A9l96MPAdvpZkAA04IVSsfB676g09yb2Ktx53JFUXEJiKvLB5cUf8ngexP3GnZGCJ2e3mVUkykNjNT6vzg/sadojqBpxffwMAEomJPBNjfxW2A8r5+DyKm9PEueJv0858= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rMYtleXj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rMYtleXj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EEE59C2BC9E; Tue, 10 Mar 2026 14:35:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153353; bh=NNr9V78uXJ/VI+bEPvEAkQ8ULjTN/7EWompKerAAGzs=; h=Date:From:To:Cc:Subject:References:From; b=rMYtleXjiDzguqWv1FFaIf0ahhEFAFA7oAzHvxwpexplD7LCuBHOAX+ySNTlIoO39 Dk1DpbcZWU2c4pEqLIVyDOCjYnRpUAkkjPUUTE2s6GbVbfLk/2tU86/zCyiyhjt0SA rctrf8CuOnETQfDxLcQADctn418zaJUgtgu8yzMgI9FvnVTE35emyTsBx//ZvBPcaL PMh0IoIW1xMb6Lt/rToUqVjH344tat2FUHxwnGP7+oUd2i80e4Q+PzJELJFh1wNOqc JOU1kSmNFG3l0bxH6KM2SI0Jx89jwhzKjFO/OhhLkhyepy63Mr1o3m/m000z1sI6Me UejjlPjOq8jaA== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBn-00000002ZaL-0Ayx; Tue, 10 Mar 2026 10:36:03 -0400 Message-ID: <20260310143602.907472935@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:17 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 02/18] ring-buffer: Store bpage pointers into subbuf_ids References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort The subbuf_ids field allows to point to a specific page from the ring-buffer based on its ID. As a preparation or the upcoming ring-buffer remote support, point this array to the buffer_page instead of the buffer_data_page. Link: https://patch.msgid.link/20260309162516.2623589-3-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 82b4df579670..3d2804a7e8ab 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -555,7 +555,7 @@ struct ring_buffer_per_cpu { unsigned int mapped; unsigned int user_mapped; /* user space mapping */ struct mutex mapping_lock; - unsigned long *subbuf_ids; /* ID to subbuf VA */ + struct buffer_page **subbuf_ids; /* ID to subbuf VA */ struct trace_buffer_meta *meta_page; struct ring_buffer_cpu_meta *ring_meta; =20 @@ -7036,7 +7036,7 @@ static void rb_free_meta_page(struct ring_buffer_per_= cpu *cpu_buffer) } =20 static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, - unsigned long *subbuf_ids) + struct buffer_page **subbuf_ids) { struct trace_buffer_meta *meta =3D cpu_buffer->meta_page; unsigned int nr_subbufs =3D cpu_buffer->nr_pages + 1; @@ -7045,7 +7045,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer= _per_cpu *cpu_buffer, int id =3D 0; =20 id =3D rb_page_id(cpu_buffer, cpu_buffer->reader_page, id); - subbuf_ids[id++] =3D (unsigned long)cpu_buffer->reader_page->page; + subbuf_ids[id++] =3D cpu_buffer->reader_page; cnt++; =20 first_subbuf =3D subbuf =3D rb_set_head_page(cpu_buffer); @@ -7055,7 +7055,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer= _per_cpu *cpu_buffer, if (WARN_ON(id >=3D nr_subbufs)) break; =20 - subbuf_ids[id] =3D (unsigned long)subbuf->page; + subbuf_ids[id] =3D subbuf; =20 rb_inc_page(&subbuf); id++; @@ -7064,7 +7064,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer= _per_cpu *cpu_buffer, =20 WARN_ON(cnt !=3D nr_subbufs); =20 - /* install subbuf ID to kern VA translation */ + /* install subbuf ID to bpage translation */ cpu_buffer->subbuf_ids =3D subbuf_ids; =20 meta->meta_struct_len =3D sizeof(*meta); @@ -7220,13 +7220,15 @@ static int __rb_map_vma(struct ring_buffer_per_cpu = *cpu_buffer, } =20 while (p < nr_pages) { + struct buffer_page *subbuf; struct page *page; int off =3D 0; =20 if (WARN_ON_ONCE(s >=3D nr_subbufs)) return -EINVAL; =20 - page =3D virt_to_page((void *)cpu_buffer->subbuf_ids[s]); + subbuf =3D cpu_buffer->subbuf_ids[s]; + page =3D virt_to_page((void *)subbuf->page); =20 for (; off < (1 << (subbuf_order)); off++, page++) { if (p >=3D nr_pages) @@ -7253,7 +7255,8 @@ int ring_buffer_map(struct trace_buffer *buffer, int = cpu, struct vm_area_struct *vma) { struct ring_buffer_per_cpu *cpu_buffer; - unsigned long flags, *subbuf_ids; + struct buffer_page **subbuf_ids; + unsigned long flags; int err; =20 if (!cpumask_test_cpu(cpu, buffer->cpumask)) @@ -7277,7 +7280,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int = cpu, if (err) return err; =20 - /* subbuf_ids include the reader while nr_pages does not */ + /* subbuf_ids includes the reader while nr_pages does not */ subbuf_ids =3D kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP= _KERNEL); if (!subbuf_ids) { rb_free_meta_page(cpu_buffer); --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D73C2EA754 for ; 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charset="utf-8" From: Vincent Donnefort Add ring-buffer remotes to support entities outside of the kernel (such as firmware or a hypervisor) that writes events into a ring-buffer using the tracefs format Require a description of the ring-buffer pages (struct trace_buffer_desc) and callbacks (swap_reader_page and reset) to set up the ring-buffer on the kernel side. Expect the remote entity to maintain and update the meta-page. Link: https://patch.msgid.link/20260309162516.2623589-4-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/ring_buffer.h | 58 +++++++++ kernel/trace/ring_buffer.c | 233 ++++++++++++++++++++++++++++++++++-- 2 files changed, 283 insertions(+), 8 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index d862fa610270..994f52b34344 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -251,4 +251,62 @@ int ring_buffer_map(struct trace_buffer *buffer, int c= pu, void ring_buffer_map_dup(struct trace_buffer *buffer, int cpu); int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu); + +struct ring_buffer_desc { + int cpu; + unsigned int nr_page_va; /* excludes the meta page */ + unsigned long meta_va; + unsigned long page_va[] __counted_by(nr_page_va); +}; + +struct trace_buffer_desc { + int nr_cpus; + size_t struct_len; + char __data[]; /* list of ring_buffer_desc */ +}; + +static inline struct ring_buffer_desc *__next_ring_buffer_desc(struct ring= _buffer_desc *desc) +{ + size_t len =3D struct_size(desc, page_va, desc->nr_page_va); + + return (struct ring_buffer_desc *)((void *)desc + len); +} + +static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct tra= ce_buffer_desc *desc) +{ + return (struct ring_buffer_desc *)(&desc->__data[0]); +} + +static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned i= nt nr_cpus) +{ + unsigned int nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) = + 1; + struct ring_buffer_desc *rbdesc; + + return size_add(offsetof(struct trace_buffer_desc, __data), + size_mul(nr_cpus, struct_size(rbdesc, page_va, nr_pages))); +} + +#define for_each_ring_buffer_desc(__pdesc, __cpu, __trace_pdesc) \ + for (__pdesc =3D __first_ring_buffer_desc(__trace_pdesc), __cpu =3D 0; \ + (__cpu) < (__trace_pdesc)->nr_cpus; \ + (__cpu)++, __pdesc =3D __next_ring_buffer_desc(__pdesc)) + +struct ring_buffer_remote { + struct trace_buffer_desc *desc; + int (*swap_reader_page)(unsigned int cpu, void *priv); + int (*reset)(unsigned int cpu, void *priv); + void *priv; +}; + +int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu); + +struct trace_buffer * +__ring_buffer_alloc_remote(struct ring_buffer_remote *remote, + struct lock_class_key *key); + +#define ring_buffer_alloc_remote(remote) \ +({ \ + static struct lock_class_key __key; \ + __ring_buffer_alloc_remote(remote, &__key); \ +}) #endif /* _LINUX_RING_BUFFER_H */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3d2804a7e8ab..88218377fa29 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -559,6 +559,8 @@ struct ring_buffer_per_cpu { struct trace_buffer_meta *meta_page; struct ring_buffer_cpu_meta *ring_meta; =20 + struct ring_buffer_remote *remote; + /* ring buffer pages to update, > 0 to add, < 0 to remove */ long nr_pages_to_update; struct list_head new_pages; /* new pages to add */ @@ -581,6 +583,8 @@ struct trace_buffer { =20 struct ring_buffer_per_cpu **buffers; =20 + struct ring_buffer_remote *remote; + struct hlist_node node; u64 (*clock)(void); =20 @@ -2238,6 +2242,40 @@ static void rb_meta_buffer_update(struct ring_buffer= _per_cpu *cpu_buffer, } } =20 +static struct ring_buffer_desc *ring_buffer_desc(struct trace_buffer_desc = *trace_desc, int cpu) +{ + struct ring_buffer_desc *desc, *end; + size_t len; + int i; + + if (!trace_desc) + return NULL; + + if (cpu >=3D trace_desc->nr_cpus) + return NULL; + + end =3D (struct ring_buffer_desc *)((void *)trace_desc + trace_desc->stru= ct_len); + desc =3D __first_ring_buffer_desc(trace_desc); + len =3D struct_size(desc, page_va, desc->nr_page_va); + desc =3D (struct ring_buffer_desc *)((void *)desc + (len * cpu)); + + if (desc < end && desc->cpu =3D=3D cpu) + return desc; + + /* Missing CPUs, need to linear search */ + for_each_ring_buffer_desc(desc, i, trace_desc) { + if (desc->cpu =3D=3D cpu) + return desc; + } + + return NULL; +} + +static void *ring_buffer_desc_page(struct ring_buffer_desc *desc, int page= _id) +{ + return page_id > desc->nr_page_va ? NULL : (void *)desc->page_va[page_id]; +} + static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, long nr_pages, struct list_head *pages) { @@ -2245,6 +2283,7 @@ static int __rb_allocate_pages(struct ring_buffer_per= _cpu *cpu_buffer, struct ring_buffer_cpu_meta *meta =3D NULL; struct buffer_page *bpage, *tmp; bool user_thread =3D current->mm !=3D NULL; + struct ring_buffer_desc *desc =3D NULL; long i; =20 /* @@ -2273,6 +2312,12 @@ static int __rb_allocate_pages(struct ring_buffer_pe= r_cpu *cpu_buffer, if (buffer->range_addr_start) meta =3D rb_range_meta(buffer, nr_pages, cpu_buffer->cpu); =20 + if (buffer->remote) { + desc =3D ring_buffer_desc(buffer->remote->desc, cpu_buffer->cpu); + if (!desc || WARN_ON(desc->nr_page_va !=3D (nr_pages + 1))) + return -EINVAL; + } + for (i =3D 0; i < nr_pages; i++) { =20 bpage =3D alloc_cpu_page(cpu_buffer->cpu); @@ -2297,6 +2342,16 @@ static int __rb_allocate_pages(struct ring_buffer_pe= r_cpu *cpu_buffer, rb_meta_buffer_update(cpu_buffer, bpage); bpage->range =3D 1; bpage->id =3D i + 1; + } else if (desc) { + void *p =3D ring_buffer_desc_page(desc, i + 1); + + if (WARN_ON(!p)) + goto free_pages; + + bpage->page =3D p; + bpage->range =3D 1; /* bpage->page can't be freed */ + bpage->id =3D i + 1; + cpu_buffer->subbuf_ids[i + 1] =3D bpage; } else { int order =3D cpu_buffer->buffer->subbuf_order; bpage->page =3D alloc_cpu_data(cpu_buffer->cpu, order); @@ -2394,6 +2449,30 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, = long nr_pages, int cpu) if (cpu_buffer->ring_meta->head_buffer) rb_meta_buffer_update(cpu_buffer, bpage); bpage->range =3D 1; + } else if (buffer->remote) { + struct ring_buffer_desc *desc =3D ring_buffer_desc(buffer->remote->desc,= cpu); + + if (!desc) + goto fail_free_reader; + + cpu_buffer->remote =3D buffer->remote; + cpu_buffer->meta_page =3D (struct trace_buffer_meta *)(void *)desc->meta= _va; + cpu_buffer->nr_pages =3D nr_pages; + cpu_buffer->subbuf_ids =3D kcalloc(cpu_buffer->nr_pages + 1, + sizeof(*cpu_buffer->subbuf_ids), GFP_KERNEL); + if (!cpu_buffer->subbuf_ids) + goto fail_free_reader; + + /* Remote buffers are read-only and immutable */ + atomic_inc(&cpu_buffer->record_disabled); + atomic_inc(&cpu_buffer->resize_disabled); + + bpage->page =3D ring_buffer_desc_page(desc, cpu_buffer->meta_page->reade= r.id); + if (!bpage->page) + goto fail_free_reader; + + bpage->range =3D 1; + cpu_buffer->subbuf_ids[0] =3D bpage; } else { int order =3D cpu_buffer->buffer->subbuf_order; bpage->page =3D alloc_cpu_data(cpu, order); @@ -2453,6 +2532,9 @@ static void rb_free_cpu_buffer(struct ring_buffer_per= _cpu *cpu_buffer) =20 irq_work_sync(&cpu_buffer->irq_work.work); =20 + if (cpu_buffer->remote) + kfree(cpu_buffer->subbuf_ids); + free_buffer_page(cpu_buffer->reader_page); =20 if (head) { @@ -2475,7 +2557,8 @@ static struct trace_buffer *alloc_buffer(unsigned lon= g size, unsigned flags, int order, unsigned long start, unsigned long end, unsigned long scratch_size, - struct lock_class_key *key) + struct lock_class_key *key, + struct ring_buffer_remote *remote) { struct trace_buffer *buffer __free(kfree) =3D NULL; long nr_pages; @@ -2515,6 +2598,8 @@ static struct trace_buffer *alloc_buffer(unsigned lon= g size, unsigned flags, if (!buffer->buffers) goto fail_free_cpumask; =20 + cpu =3D raw_smp_processor_id(); + /* If start/end are specified, then that overrides size */ if (start && end) { unsigned long buffers_start; @@ -2570,6 +2655,15 @@ static struct trace_buffer *alloc_buffer(unsigned lo= ng size, unsigned flags, buffer->range_addr_end =3D end; =20 rb_range_meta_init(buffer, nr_pages, scratch_size); + } else if (remote) { + struct ring_buffer_desc *desc =3D ring_buffer_desc(remote->desc, cpu); + + buffer->remote =3D remote; + /* The writer is remote. This ring-buffer is read-only */ + atomic_inc(&buffer->record_disabled); + nr_pages =3D desc->nr_page_va - 1; + if (nr_pages < 2) + goto fail_free_buffers; } else { =20 /* need at least two pages */ @@ -2578,7 +2672,6 @@ static struct trace_buffer *alloc_buffer(unsigned lon= g size, unsigned flags, nr_pages =3D 2; } =20 - cpu =3D raw_smp_processor_id(); cpumask_set_cpu(cpu, buffer->cpumask); buffer->buffers[cpu] =3D rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) @@ -2620,7 +2713,7 @@ struct trace_buffer *__ring_buffer_alloc(unsigned lon= g size, unsigned flags, struct lock_class_key *key) { /* Default buffer page size - one system page */ - return alloc_buffer(size, flags, 0, 0, 0, 0, key); + return alloc_buffer(size, flags, 0, 0, 0, 0, key, NULL); =20 } EXPORT_SYMBOL_GPL(__ring_buffer_alloc); @@ -2647,7 +2740,18 @@ struct trace_buffer *__ring_buffer_alloc_range(unsig= ned long size, unsigned flag struct lock_class_key *key) { return alloc_buffer(size, flags, order, start, start + range_size, - scratch_size, key); + scratch_size, key, NULL); +} + +/** + * __ring_buffer_alloc_remote - allocate a new ring_buffer from a remote + * @remote: Contains a description of the ring-buffer pages and remote cal= lbacks. + * @key: ring buffer reader_lock_key. + */ +struct trace_buffer *__ring_buffer_alloc_remote(struct ring_buffer_remote = *remote, + struct lock_class_key *key) +{ + return alloc_buffer(0, 0, 0, 0, 0, 0, key, remote); } =20 void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *= size) @@ -5274,6 +5378,16 @@ unsigned long ring_buffer_overruns(struct trace_buff= er *buffer) } EXPORT_SYMBOL_GPL(ring_buffer_overruns); =20 +static bool rb_read_remote_meta_page(struct ring_buffer_per_cpu *cpu_buffe= r) +{ + local_set(&cpu_buffer->entries, READ_ONCE(cpu_buffer->meta_page->entries)= ); + local_set(&cpu_buffer->overrun, READ_ONCE(cpu_buffer->meta_page->overrun)= ); + local_set(&cpu_buffer->pages_touched, READ_ONCE(cpu_buffer->meta_page->pa= ges_touched)); + local_set(&cpu_buffer->pages_lost, READ_ONCE(cpu_buffer->meta_page->pages= _lost)); + + return rb_num_of_entries(cpu_buffer); +} + static void rb_iter_reset(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer =3D iter->cpu_buffer; @@ -5428,7 +5542,43 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *i= ter, } =20 static struct buffer_page * -rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) +__rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct buffer_page *new_reader, *prev_reader; + + if (!rb_read_remote_meta_page(cpu_buffer)) + return NULL; + + /* More to read on the reader page */ + if (cpu_buffer->reader_page->read < rb_page_size(cpu_buffer->reader_page)= ) { + if (!cpu_buffer->reader_page->read) + cpu_buffer->read_stamp =3D cpu_buffer->reader_page->page->time_stamp; + return cpu_buffer->reader_page; + } + + prev_reader =3D cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id]; + + WARN_ON_ONCE(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, + cpu_buffer->remote->priv)); + /* nr_pages doesn't include the reader page */ + if (WARN_ON_ONCE(cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages)) + return NULL; + + new_reader =3D cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id]; + + WARN_ON_ONCE(prev_reader =3D=3D new_reader); + + cpu_buffer->reader_page->page =3D new_reader->page; + cpu_buffer->reader_page->id =3D new_reader->id; + cpu_buffer->reader_page->read =3D 0; + cpu_buffer->read_stamp =3D cpu_buffer->reader_page->page->time_stamp; + cpu_buffer->lost_events =3D cpu_buffer->meta_page->reader.lost_events; + + return rb_page_size(cpu_buffer->reader_page) ? cpu_buffer->reader_page : = NULL; +} + +static struct buffer_page * +__rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *reader =3D NULL; unsigned long bsize =3D READ_ONCE(cpu_buffer->buffer->subbuf_size); @@ -5598,6 +5748,13 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_b= uffer) return reader; } =20 +static struct buffer_page * +rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + return cpu_buffer->remote ? __rb_get_reader_page_from_remote(cpu_buffer) : + __rb_get_reader_page(cpu_buffer); +} + static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer) { struct ring_buffer_event *event; @@ -5998,7 +6155,7 @@ ring_buffer_read_start(struct trace_buffer *buffer, i= nt cpu, gfp_t flags) struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_iter *iter; =20 - if (!cpumask_test_cpu(cpu, buffer->cpumask)) + if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->remote) return NULL; =20 iter =3D kzalloc_obj(*iter, flags); @@ -6166,6 +6323,23 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *page; =20 + if (cpu_buffer->remote) { + if (!cpu_buffer->remote->reset) + return; + + cpu_buffer->remote->reset(cpu_buffer->cpu, cpu_buffer->remote->priv); + rb_read_remote_meta_page(cpu_buffer); + + /* Read related values, not covered by the meta-page */ + local_set(&cpu_buffer->pages_read, 0); + cpu_buffer->read =3D 0; + cpu_buffer->read_bytes =3D 0; + cpu_buffer->last_overrun =3D 0; + cpu_buffer->reader_page->read =3D 0; + + return; + } + rb_head_page_deactivate(cpu_buffer); =20 cpu_buffer->head_page @@ -6396,6 +6570,46 @@ bool ring_buffer_empty_cpu(struct trace_buffer *buff= er, int cpu) } EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu); =20 +int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (cpu !=3D RING_BUFFER_ALL_CPUS) { + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer =3D buffer->buffers[cpu]; + + guard(raw_spinlock)(&cpu_buffer->reader_lock); + if (rb_read_remote_meta_page(cpu_buffer)) + rb_wakeups(buffer, cpu_buffer); + + return 0; + } + + guard(cpus_read_lock)(); + + /* + * Make sure all the ring buffers are up to date before we start reading + * them. + */ + for_each_buffer_cpu(buffer, cpu) { + cpu_buffer =3D buffer->buffers[cpu]; + + guard(raw_spinlock)(&cpu_buffer->reader_lock); + rb_read_remote_meta_page(cpu_buffer); + } + + for_each_buffer_cpu(buffer, cpu) { + cpu_buffer =3D buffer->buffers[cpu]; + + if (rb_num_of_entries(cpu_buffer)) + rb_wakeups(buffer, cpu_buffer); + } + + return 0; +} + #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP /** * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers @@ -6634,6 +6848,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, unsigned int commit; unsigned int read; u64 save_timestamp; + bool force_memcpy; =20 if (!cpumask_test_cpu(cpu, buffer->cpumask)) return -1; @@ -6671,6 +6886,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer, /* Check if any events were dropped */ missed_events =3D cpu_buffer->lost_events; =20 + force_memcpy =3D cpu_buffer->mapped || cpu_buffer->remote; + /* * If this page has been partially read or * if len is not big enough to read the rest of the page or @@ -6680,7 +6897,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, */ if (read || (len < (commit - read)) || cpu_buffer->reader_page =3D=3D cpu_buffer->commit_page || - cpu_buffer->mapped) { + force_memcpy) { struct buffer_data_page *rpage =3D cpu_buffer->reader_page->page; unsigned int rpos =3D read; unsigned int pos =3D 0; 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Tue, 10 Mar 2026 10:36:03 -0400 Message-ID: <20260310143603.219118299@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:19 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 04/18] ring-buffer: Add non-consuming read for ring-buffer remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Hopefully, the remote will only swap pages on the kernel instruction (via the swap_reader_page() callback). This means we know at what point the ring-buffer geometry has changed. It is therefore possible to rearrange the kernel view of that ring-buffer to allow non-consuming read. Link: https://patch.msgid.link/20260309162516.2623589-5-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 75 +++++++++++++++++++++++++++++++++++--- 1 file changed, 69 insertions(+), 6 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 88218377fa29..fb39dd43e00b 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5388,10 +5388,51 @@ static bool rb_read_remote_meta_page(struct ring_bu= ffer_per_cpu *cpu_buffer) return rb_num_of_entries(cpu_buffer); } =20 +static void rb_update_remote_head(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct buffer_page *next, *orig; + int retry =3D 3; + + orig =3D next =3D cpu_buffer->head_page; + rb_inc_page(&next); + + /* Run after the writer */ + while (cpu_buffer->head_page->page->time_stamp > next->page->time_stamp) { + rb_inc_page(&next); + + rb_list_head_clear(cpu_buffer->head_page->list.prev); + rb_inc_page(&cpu_buffer->head_page); + rb_set_list_to_head(cpu_buffer->head_page->list.prev); + + if (cpu_buffer->head_page =3D=3D orig) { + if (WARN_ON_ONCE(!(--retry))) + return; + } + } + + orig =3D cpu_buffer->commit_page =3D cpu_buffer->head_page; + retry =3D 3; + + while (cpu_buffer->commit_page->page->time_stamp < next->page->time_stamp= ) { + rb_inc_page(&next); + rb_inc_page(&cpu_buffer->commit_page); + + if (cpu_buffer->commit_page =3D=3D orig) { + if (WARN_ON_ONCE(!(--retry))) + return; + } + } +} + static void rb_iter_reset(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer =3D iter->cpu_buffer; =20 + if (cpu_buffer->remote) { + rb_read_remote_meta_page(cpu_buffer); + rb_update_remote_head(cpu_buffer); + } + /* Iterator usage is expected to have record disabled */ iter->head_page =3D cpu_buffer->reader_page; iter->head =3D cpu_buffer->reader_page->read; @@ -5544,7 +5585,7 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *it= er, static struct buffer_page * __rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer) { - struct buffer_page *new_reader, *prev_reader; + struct buffer_page *new_reader, *prev_reader, *prev_head, *new_head, *las= t; =20 if (!rb_read_remote_meta_page(cpu_buffer)) return NULL; @@ -5568,10 +5609,32 @@ __rb_get_reader_page_from_remote(struct ring_buffer= _per_cpu *cpu_buffer) =20 WARN_ON_ONCE(prev_reader =3D=3D new_reader); =20 - cpu_buffer->reader_page->page =3D new_reader->page; - cpu_buffer->reader_page->id =3D new_reader->id; - cpu_buffer->reader_page->read =3D 0; - cpu_buffer->read_stamp =3D cpu_buffer->reader_page->page->time_stamp; + prev_head =3D new_reader; /* New reader was also the previous head */ + new_head =3D prev_head; + rb_inc_page(&new_head); + last =3D prev_head; + rb_dec_page(&last); + + /* Clear the old HEAD flag */ + rb_list_head_clear(cpu_buffer->head_page->list.prev); + + prev_reader->list.next =3D prev_head->list.next; + prev_reader->list.prev =3D prev_head->list.prev; + + /* Swap prev_reader with new_reader */ + last->list.next =3D &prev_reader->list; + new_head->list.prev =3D &prev_reader->list; + + new_reader->list.prev =3D &new_reader->list; + new_reader->list.next =3D &new_head->list; + + /* Reactivate the HEAD flag */ + rb_set_list_to_head(&last->list); + + cpu_buffer->head_page =3D new_head; + cpu_buffer->reader_page =3D new_reader; + cpu_buffer->pages =3D &new_head->list; + cpu_buffer->read_stamp =3D new_reader->page->time_stamp; cpu_buffer->lost_events =3D cpu_buffer->meta_page->reader.lost_events; =20 return rb_page_size(cpu_buffer->reader_page) ? cpu_buffer->reader_page : = NULL; @@ -6155,7 +6218,7 @@ ring_buffer_read_start(struct trace_buffer *buffer, i= nt cpu, gfp_t flags) struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_iter *iter; =20 - if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->remote) + if (!cpumask_test_cpu(cpu, buffer->cpumask)) return NULL; =20 iter =3D kzalloc_obj(*iter, flags); --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B59EA2ECEA0 for ; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; cv=none; b=e/9laqTHD1pPJPOg4NbF6760n9ZkOQJd3O99pVZjkTOU+jkUhBTIEQZzGx3fxfs3vSF8E7lFE+BwcMmhSLcpoFvw8oBf406HaGP4mXWssi2t66mLgHCfDu1IATWYoWtCmJyjbxnZ/iO84e6OpkmjVI1TMJ3l3cub+CPu1zKBn7o= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; c=relaxed/simple; bh=ygBIiW+eiijfG7UHCcpN4CWSymvYdnHxoMED9SF6guI=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=Ka0AqnW2fbyncRDFUTzO0IHjk//KY4PLWEpJeWPcAq10A/IDjzctl1L29/hF0bi6ggCMZSSgeYUxjAUJQsu0dd/ccTtWy1HpZJ1xv7RBztUa8NqbFHUilcF4NFkD38Bpi8YZukj7qrL6VeGl83c4vyBCp+ENBwWY6L4m4TmpVC8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fzYxBJL/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fzYxBJL/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B578C19425; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153353; bh=ygBIiW+eiijfG7UHCcpN4CWSymvYdnHxoMED9SF6guI=; h=Date:From:To:Cc:Subject:References:From; b=fzYxBJL/m1+3gwNVIPRKsevzZGZtviSzRSZjn18EJi5cDMxYx2eJ5LrlbUtKQiBCx 5QJjNQpaeYtcagKgcBM7WmyWElXvPZvokHN1Hg20ZOPTXX9gZCoupZmGZSGFybnMxo zAAJ8TX+4VX89Jvwa7QKFd1a8mNhNzzgYYEIlZaoJup3NpmTPLLgesgcLrRYtovgk8 QBfOL4Ans0CWTXgNBMAuGW3GTb7zkx3qsJsYQEjw72Wv2N66bsnuSfyQ+a0zivMuoK /6Decik4Oh2LyjlHpVWKgOVmgoNr8WGfqmKk0veTJo3futLISg+lmNfn8tFHZxFqi2 1VDBStDO3BAVA== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBn-00000002Zbo-2C7Y; Tue, 10 Mar 2026 10:36:03 -0400 Message-ID: <20260310143603.381421878@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:20 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 05/18] tracing: Introduce trace remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort A trace remote relies on ring-buffer remotes to read and control compatible tracing buffers, written by entity such as firmware or hypervisor. Add a Tracefs directory remotes/ that contains all instances of trace remotes. Each instance follows the same hierarchy as any other to ease the support by existing user-space tools. This currently does not provide any event support, which will come later. Link: https://patch.msgid.link/20260309162516.2623589-6-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/trace_remote.h | 36 ++ kernel/trace/Kconfig | 3 + kernel/trace/Makefile | 1 + kernel/trace/trace.c | 2 +- kernel/trace/trace.h | 6 + kernel/trace/trace_remote.c | 619 +++++++++++++++++++++++++++++++++++ 6 files changed, 666 insertions(+), 1 deletion(-) create mode 100644 include/linux/trace_remote.h create mode 100644 kernel/trace/trace_remote.c diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h new file mode 100644 index 000000000000..65b7e7b8267c --- /dev/null +++ b/include/linux/trace_remote.h @@ -0,0 +1,36 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _LINUX_TRACE_REMOTE_H +#define _LINUX_TRACE_REMOTE_H + +#include + +/** + * struct trace_remote_callbacks - Callbacks used by Tracefs to control th= e remote + * @load_trace_buffer: Called before Tracefs accesses the trace buffer fo= r the first + * time. Must return a &trace_buffer_desc + * (most likely filled with trace_remote_alloc_buffer()) + * @unload_trace_buffer: + * Called once Tracefs has no use for the trace buffer + * (most likely call trace_remote_free_buffer()) + * @enable_tracing: Called on Tracefs tracing_on. It is expected from the + * remote to allow writing. + * @swap_reader_page: Called when Tracefs consumes a new page from a + * ring-buffer. It is expected from the remote to isolate a + * new reader-page from the @cpu ring-buffer. + */ +struct trace_remote_callbacks { + struct trace_buffer_desc *(*load_trace_buffer)(unsigned long size, void *= priv); + void (*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv); + int (*enable_tracing)(bool enable, void *priv); + int (*swap_reader_page)(unsigned int cpu, void *priv); +}; + +int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv); + +int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_= size, size_t buffer_size, + const struct cpumask *cpumask); + +void trace_remote_free_buffer(struct trace_buffer_desc *desc); + +#endif diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 49de13cae428..384dd36c8e29 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -1281,4 +1281,7 @@ config HIST_TRIGGERS_DEBUG =20 source "kernel/trace/rv/Kconfig" =20 +config TRACE_REMOTE + bool + endif # FTRACE diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 04096c21d06b..318923ce39f5 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -128,4 +128,5 @@ obj-$(CONFIG_FPROBE_EVENTS) +=3D trace_fprobe.o obj-$(CONFIG_TRACEPOINT_BENCHMARK) +=3D trace_benchmark.o obj-$(CONFIG_RV) +=3D rv/ =20 +obj-$(CONFIG_TRACE_REMOTE) +=3D trace_remote.o libftrace-y :=3D ftrace.o diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ebd996f8710e..e33cb3c39f6e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8589,7 +8589,7 @@ static struct dentry *tracing_dentry_percpu(struct tr= ace_array *tr, int cpu) return tr->percpu_dir; } =20 -static struct dentry * +struct dentry * trace_create_cpu_file(const char *name, umode_t mode, struct dentry *paren= t, void *data, long cpu, const struct file_operations *fops) { diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index b8f3804586a0..d6af4405b341 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -689,6 +689,12 @@ struct dentry *trace_create_file(const char *name, struct dentry *parent, void *data, const struct file_operations *fops); +struct dentry *trace_create_cpu_file(const char *name, + umode_t mode, + struct dentry *parent, + void *data, + long cpu, + const struct file_operations *fops); =20 =20 /** diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c new file mode 100644 index 000000000000..8b06f730376e --- /dev/null +++ b/kernel/trace/trace_remote.c @@ -0,0 +1,619 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2025 - Google LLC + * Author: Vincent Donnefort + */ + +#include +#include +#include +#include +#include +#include +#include + +#include "trace.h" + +#define TRACEFS_DIR "remotes" +#define TRACEFS_MODE_WRITE 0640 +#define TRACEFS_MODE_READ 0440 + +struct trace_remote_iterator { + struct trace_remote *remote; + struct trace_seq seq; + struct delayed_work poll_work; + unsigned long lost_events; + u64 ts; + int cpu; + int evt_cpu; +}; + +struct trace_remote { + struct trace_remote_callbacks *cbs; + void *priv; + struct trace_buffer *trace_buffer; + struct trace_buffer_desc *trace_buffer_desc; + unsigned long trace_buffer_size; + struct ring_buffer_remote rb_remote; + struct mutex lock; + unsigned int nr_readers; + unsigned int poll_ms; + bool tracing_on; +}; + +static bool trace_remote_loaded(struct trace_remote *remote) +{ + return !!remote->trace_buffer; +} + +static int trace_remote_load(struct trace_remote *remote) +{ + struct ring_buffer_remote *rb_remote =3D &remote->rb_remote; + struct trace_buffer_desc *desc; + + lockdep_assert_held(&remote->lock); + + if (trace_remote_loaded(remote)) + return 0; + + desc =3D remote->cbs->load_trace_buffer(remote->trace_buffer_size, remote= ->priv); + if (IS_ERR(desc)) + return PTR_ERR(desc); + + rb_remote->desc =3D desc; + rb_remote->swap_reader_page =3D remote->cbs->swap_reader_page; + rb_remote->priv =3D remote->priv; + remote->trace_buffer =3D ring_buffer_alloc_remote(rb_remote); + if (!remote->trace_buffer) { + remote->cbs->unload_trace_buffer(desc, remote->priv); + return -ENOMEM; + } + + remote->trace_buffer_desc =3D desc; + + return 0; +} + +static void trace_remote_try_unload(struct trace_remote *remote) +{ + lockdep_assert_held(&remote->lock); + + if (!trace_remote_loaded(remote)) + return; + + /* The buffer is being read or writable */ + if (remote->nr_readers || remote->tracing_on) + return; + + /* The buffer has readable data */ + if (!ring_buffer_empty(remote->trace_buffer)) + return; + + ring_buffer_free(remote->trace_buffer); + remote->trace_buffer =3D NULL; + remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv); +} + +static int trace_remote_enable_tracing(struct trace_remote *remote) +{ + int ret; + + lockdep_assert_held(&remote->lock); + + if (remote->tracing_on) + return 0; + + ret =3D trace_remote_load(remote); + if (ret) + return ret; + + ret =3D remote->cbs->enable_tracing(true, remote->priv); + if (ret) { + trace_remote_try_unload(remote); + return ret; + } + + remote->tracing_on =3D true; + + return 0; +} + +static int trace_remote_disable_tracing(struct trace_remote *remote) +{ + int ret; + + lockdep_assert_held(&remote->lock); + + if (!remote->tracing_on) + return 0; + + ret =3D remote->cbs->enable_tracing(false, remote->priv); + if (ret) + return ret; + + ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS); + remote->tracing_on =3D false; + trace_remote_try_unload(remote); + + return 0; +} + +static ssize_t +tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, l= off_t *ppos) +{ + struct trace_remote *remote =3D filp->private_data; + unsigned long val; + int ret; + + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + ret =3D val ? trace_remote_enable_tracing(remote) : trace_remote_disable_= tracing(remote); + if (ret) + return ret; + + return cnt; +} +static int tracing_on_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote =3D s->private; + + seq_printf(s, "%d\n", remote->tracing_on); + + return 0; +} +DEFINE_SHOW_STORE_ATTRIBUTE(tracing_on); + +static ssize_t buffer_size_kb_write(struct file *filp, const char __user *= ubuf, size_t cnt, + loff_t *ppos) +{ + struct trace_remote *remote =3D filp->private_data; + unsigned long val; + int ret; + + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); + if (ret) + return ret; + + /* KiB to Bytes */ + if (!val || check_shl_overflow(val, 10, &val)) + return -EINVAL; + + guard(mutex)(&remote->lock); + + if (trace_remote_loaded(remote)) + return -EBUSY; + + remote->trace_buffer_size =3D val; + + return cnt; +} + +static int buffer_size_kb_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote =3D s->private; + + seq_printf(s, "%lu (%s)\n", remote->trace_buffer_size >> 10, + trace_remote_loaded(remote) ? "loaded" : "unloaded"); + + return 0; +} +DEFINE_SHOW_STORE_ATTRIBUTE(buffer_size_kb); + +static int trace_remote_get(struct trace_remote *remote, int cpu) +{ + int ret; + + if (remote->nr_readers =3D=3D UINT_MAX) + return -EBUSY; + + ret =3D trace_remote_load(remote); + if (ret) + return ret; + + remote->nr_readers++; + + return 0; +} + +static void trace_remote_put(struct trace_remote *remote) +{ + if (WARN_ON(!remote->nr_readers)) + return; + + remote->nr_readers--; + if (remote->nr_readers) + return; + + trace_remote_try_unload(remote); +} + +static void __poll_remote(struct work_struct *work) +{ + struct delayed_work *dwork =3D to_delayed_work(work); + struct trace_remote_iterator *iter; + + iter =3D container_of(dwork, struct trace_remote_iterator, poll_work); + ring_buffer_poll_remote(iter->remote->trace_buffer, iter->cpu); + schedule_delayed_work((struct delayed_work *)work, + msecs_to_jiffies(iter->remote->poll_ms)); +} + +static struct trace_remote_iterator *trace_remote_iter(struct trace_remote= *remote, int cpu) +{ + struct trace_remote_iterator *iter =3D NULL; + int ret; + + lockdep_assert_held(&remote->lock); + + + ret =3D trace_remote_get(remote, cpu); + if (ret) + return ERR_PTR(ret); + + /* Test the CPU */ + ret =3D ring_buffer_poll_remote(remote->trace_buffer, cpu); + if (ret) + goto err; + + iter =3D kzalloc_obj(*iter); + if (iter) { + iter->remote =3D remote; + iter->cpu =3D cpu; + trace_seq_init(&iter->seq); + INIT_DELAYED_WORK(&iter->poll_work, __poll_remote); + schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms= )); + + return iter; + } + ret =3D -ENOMEM; + +err: + kfree(iter); + trace_remote_put(remote); + + return ERR_PTR(ret); +} + +static void trace_remote_iter_free(struct trace_remote_iterator *iter) +{ + struct trace_remote *remote; + + if (!iter) + return; + + remote =3D iter->remote; + + lockdep_assert_held(&remote->lock); + + kfree(iter); + trace_remote_put(remote); +} + +static bool trace_remote_iter_read_event(struct trace_remote_iterator *ite= r) +{ + struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; + int cpu =3D iter->cpu; + + if (cpu !=3D RING_BUFFER_ALL_CPUS) { + if (ring_buffer_empty_cpu(trace_buffer, cpu)) + return false; + + if (!ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events)) + return false; + + iter->evt_cpu =3D cpu; + return true; + } + + iter->ts =3D U64_MAX; + for_each_possible_cpu(cpu) { + unsigned long lost_events; + u64 ts; + + if (ring_buffer_empty_cpu(trace_buffer, cpu)) + continue; + + if (!ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events)) + continue; + + if (ts >=3D iter->ts) + continue; + + iter->ts =3D ts; + iter->evt_cpu =3D cpu; + iter->lost_events =3D lost_events; + } + + return iter->ts !=3D U64_MAX; +} + +static int trace_remote_iter_print_event(struct trace_remote_iterator *ite= r) +{ + unsigned long usecs_rem; + u64 ts =3D iter->ts; + + if (iter->lost_events) + trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n", + iter->evt_cpu, iter->lost_events); + + do_div(ts, 1000); + usecs_rem =3D do_div(ts, USEC_PER_SEC); + + trace_seq_printf(&iter->seq, "[%03d]\t%5llu.%06lu: ", iter->evt_cpu, + ts, usecs_rem); + + return trace_seq_has_overflowed(&iter->seq) ? -EOVERFLOW : 0; +} + +static int trace_pipe_open(struct inode *inode, struct file *filp) +{ + struct trace_remote *remote =3D inode->i_private; + struct trace_remote_iterator *iter; + int cpu =3D RING_BUFFER_ALL_CPUS; + + if (inode->i_cdev) + cpu =3D (long)inode->i_cdev - 1; + + guard(mutex)(&remote->lock); + iter =3D trace_remote_iter(remote, cpu); + filp->private_data =3D iter; + + return IS_ERR(iter) ? PTR_ERR(iter) : 0; +} + +static int trace_pipe_release(struct inode *inode, struct file *filp) +{ + struct trace_remote_iterator *iter =3D filp->private_data; + struct trace_remote *remote =3D iter->remote; + + guard(mutex)(&remote->lock); + + trace_remote_iter_free(iter); + + return 0; +} + +static ssize_t trace_pipe_read(struct file *filp, char __user *ubuf, size_= t cnt, loff_t *ppos) +{ + struct trace_remote_iterator *iter =3D filp->private_data; + struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; + int ret; + +copy_to_user: + ret =3D trace_seq_to_user(&iter->seq, ubuf, cnt); + if (ret !=3D -EBUSY) + return ret; + + trace_seq_init(&iter->seq); + + ret =3D ring_buffer_wait(trace_buffer, iter->cpu, 0, NULL, NULL); + if (ret < 0) + return ret; + + while (trace_remote_iter_read_event(iter)) { + int prev_len =3D iter->seq.seq.len; + + if (trace_remote_iter_print_event(iter)) { + iter->seq.seq.len =3D prev_len; + break; + } + + ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); + } + + goto copy_to_user; +} + +static const struct file_operations trace_pipe_fops =3D { + .open =3D trace_pipe_open, + .read =3D trace_pipe_read, + .release =3D trace_pipe_release, +}; + +static int trace_remote_init_tracefs(const char *name, struct trace_remote= *remote) +{ + struct dentry *remote_d, *percpu_d, *d; + static struct dentry *root; + static DEFINE_MUTEX(lock); + bool root_inited =3D false; + int cpu; + + guard(mutex)(&lock); + + if (!root) { + root =3D tracefs_create_dir(TRACEFS_DIR, NULL); + if (!root) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"\n"); + return -ENOMEM; + } + root_inited =3D true; + } + + remote_d =3D tracefs_create_dir(name, root); + if (!remote_d) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/\n", name); + goto err; + } + + d =3D trace_create_file("tracing_on", TRACEFS_MODE_WRITE, remote_d, remot= e, &tracing_on_fops); + if (!d) + goto err; + + d =3D trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, r= emote, + &buffer_size_kb_fops); + if (!d) + goto err; + + d =3D trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, remote= , &trace_pipe_fops); + if (!d) + goto err; + + percpu_d =3D tracefs_create_dir("per_cpu", remote_d); + if (!percpu_d) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name); + goto err; + } + + for_each_possible_cpu(cpu) { + struct dentry *cpu_d; + char cpu_name[16]; + + snprintf(cpu_name, sizeof(cpu_name), "cpu%d", cpu); + cpu_d =3D tracefs_create_dir(cpu_name, percpu_d); + if (!cpu_d) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/percpu/cpu%d\n", + name, cpu); + goto err; + } + + d =3D trace_create_cpu_file("trace_pipe", TRACEFS_MODE_READ, cpu_d, remo= te, cpu, + &trace_pipe_fops); + if (!d) + goto err; + } + + return 0; + +err: + if (root_inited) { + tracefs_remove(root); + root =3D NULL; + } else { + tracefs_remove(remote_d); + } + + return -ENOMEM; +} + +/** + * trace_remote_register() - Register a Tracefs remote + * @name: Name of the remote, used for the Tracefs remotes/ directory. + * @cbs: Set of callbacks used to control the remote. + * @priv: Private data, passed to each callback from @cbs. + * @events: Array of events. &remote_event.name and &remote_event.id must = be + * filled by the caller. + * @nr_events: Number of events in the @events array. + * + * A trace remote is an entity, outside of the kernel (most likely firmwar= e or + * hypervisor) capable of writing events into a Tracefs compatible ring-bu= ffer. + * The kernel would then act as a reader. + * + * The registered remote will be found under the Tracefs directory + * remotes/. + * + * Return: 0 on success, negative error code on failure. + */ +int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv) +{ + struct trace_remote *remote; + + remote =3D kzalloc_obj(*remote); + if (!remote) + return -ENOMEM; + + remote->cbs =3D cbs; + remote->priv =3D priv; + remote->trace_buffer_size =3D 7 << 10; + remote->poll_ms =3D 100; + mutex_init(&remote->lock); + + if (trace_remote_init_tracefs(name, remote)) { + kfree(remote); + return -ENOMEM; + } + + return 0; +} +EXPORT_SYMBOL_GPL(trace_remote_register); + +/** + * trace_remote_free_buffer() - Free trace buffer allocated with trace_rem= ote_alloc_buffer() + * @desc: Descriptor of the per-CPU ring-buffers, originally filled by + * trace_remote_alloc_buffer() + * + * Most likely called from &trace_remote_callbacks.unload_trace_buffer. + */ +void trace_remote_free_buffer(struct trace_buffer_desc *desc) +{ + struct ring_buffer_desc *rb_desc; + int cpu; + + for_each_ring_buffer_desc(rb_desc, cpu, desc) { + unsigned int id; + + free_page(rb_desc->meta_va); + + for (id =3D 0; id < rb_desc->nr_page_va; id++) + free_page(rb_desc->page_va[id]); + } +} +EXPORT_SYMBOL_GPL(trace_remote_free_buffer); + +/** + * trace_remote_alloc_buffer() - Dynamically allocate a trace buffer + * @desc: Uninitialized trace_buffer_desc + * @desc_size: Size of the trace_buffer_desc. Must be at least equal to + * trace_buffer_desc_size() + * @buffer_size: Size in bytes of each per-CPU ring-buffer + * @cpumask: CPUs to allocate a ring-buffer for + * + * Helper to dynamically allocate a set of pages (enough to cover @buffer_= size) + * for each CPU from @cpumask and fill @desc. Most likely called from + * &trace_remote_callbacks.load_trace_buffer. + * + * Return: 0 on success, negative error code on failure. + */ +int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_= size, size_t buffer_size, + const struct cpumask *cpumask) +{ + unsigned int nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) = + 1; + void *desc_end =3D desc + desc_size; + struct ring_buffer_desc *rb_desc; + int cpu, ret =3D -ENOMEM; + + if (desc_size < struct_size(desc, __data, 0)) + return -EINVAL; + + desc->nr_cpus =3D 0; + desc->struct_len =3D struct_size(desc, __data, 0); + + rb_desc =3D (struct ring_buffer_desc *)&desc->__data[0]; + + for_each_cpu(cpu, cpumask) { + unsigned int id; + + if ((void *)rb_desc + struct_size(rb_desc, page_va, nr_pages) > desc_end= ) { + ret =3D -EINVAL; + goto err; + } + + rb_desc->cpu =3D cpu; + rb_desc->nr_page_va =3D 0; + rb_desc->meta_va =3D (unsigned long)__get_free_page(GFP_KERNEL); + if (!rb_desc->meta_va) + goto err; + + for (id =3D 0; id < nr_pages; id++) { + rb_desc->page_va[id] =3D (unsigned long)__get_free_page(GFP_KERNEL); + if (!rb_desc->page_va[id]) + goto err; + + rb_desc->nr_page_va++; + } + desc->nr_cpus++; + desc->struct_len +=3D offsetof(struct ring_buffer_desc, page_va); + desc->struct_len +=3D struct_size(rb_desc, page_va, rb_desc->nr_page_va); + rb_desc =3D __next_ring_buffer_desc(rb_desc); + } + + return 0; + +err: + trace_remote_free_buffer(desc); + return ret; +} +EXPORT_SYMBOL_GPL(trace_remote_alloc_buffer); --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD1DD2ED16D for ; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; cv=none; b=A180ONlKDa89pTcELUrfC9MPUi7OFtvAOtVAudD2t+QuoykTywPg1Xw4o9aBaWrouRo0e644nyNaXWu/u505xsk9Kgnt5J5YkBI7WdiKaExVqPMUt3LcTMP/P2NylxTrfZf8zdcNRi7hL7gC5MoYv5HiFEqh3vOjIXsmjg1wjyQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153353; c=relaxed/simple; bh=WM3N6AZ/ouSfKUoIWUPwIx9c9hn9I0Zxf54ux3bFnGo=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=NfS1FQNEMM2Cwc7gS4ZUDNzpG/yVK3zQUcKIwsCydlSfldm/DWn/Rx135qtHmyQw1xmHDBKsgftw1I2xKqR8dCcWHI9DSwYFTFuJ2Q7x3ddgu2rK6wFSsC75O0XRSo/E5wAF35P8mODhC1JQ1LSxMOWSiRHm0y4BzktMD5o+/ro= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rCOrSc7Z; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rCOrSc7Z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98866C2BCB9; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153353; bh=WM3N6AZ/ouSfKUoIWUPwIx9c9hn9I0Zxf54ux3bFnGo=; h=Date:From:To:Cc:Subject:References:From; b=rCOrSc7ZWL6BPUjEmEmcDWYk7G1lVOwzjrM1KOLxgdvr3TDHMiDr9yzwGQEHylnzZ 0/lYvd/TPpM9GQyfWqfaWYG9Evi2NPz4k4U/t9gpBYQ+1N+NujNejCdObQT19FVqqw 6zPwrF6RZaPcqzhOyHUrPoTI8fasPt8lTT0Hn1DrxODiJjzjSVqEMMXOXSVGwDlTy8 t5ERGUvarI6iKoiGjyZUo5EwUujn9kYqLcr8RioEbZa9KubStWTnCsRV2WPkBvBmFV nrUjRquvC2wwvzT9Qixnp5v9AO6Fy1A6DwG2H9irktw58dKw4WonBhZNFwYXh6M1k5 BJBzxjiDdZFjw== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBn-00000002ZcI-2oio; Tue, 10 Mar 2026 10:36:03 -0400 Message-ID: <20260310143603.541004463@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:21 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 06/18] tracing: Add reset to trace remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Allow to reset the trace remote buffer by writing to the Tracefs "trace" file. This is similar to the regular Tracefs interface. Link: https://patch.msgid.link/20260309162516.2623589-7-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/trace_remote.h | 3 +++ kernel/trace/trace_remote.c | 45 ++++++++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+) diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h index 65b7e7b8267c..10ca03dc192b 100644 --- a/include/linux/trace_remote.h +++ b/include/linux/trace_remote.h @@ -17,6 +17,8 @@ * remote to allow writing. * @swap_reader_page: Called when Tracefs consumes a new page from a * ring-buffer. It is expected from the remote to isolate a + * @reset: Called on `echo 0 > trace`. It is expected from the + * remote to reset all ring-buffer pages. * new reader-page from the @cpu ring-buffer. */ struct trace_remote_callbacks { @@ -24,6 +26,7 @@ struct trace_remote_callbacks { void (*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv); int (*enable_tracing)(bool enable, void *priv); int (*swap_reader_page)(unsigned int cpu, void *priv); + int (*reset)(unsigned int cpu, void *priv); }; =20 int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv); diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 8b06f730376e..a7b94736dd38 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -63,6 +63,7 @@ static int trace_remote_load(struct trace_remote *remote) rb_remote->desc =3D desc; rb_remote->swap_reader_page =3D remote->cbs->swap_reader_page; rb_remote->priv =3D remote->priv; + rb_remote->reset =3D remote->cbs->reset; remote->trace_buffer =3D ring_buffer_alloc_remote(rb_remote); if (!remote->trace_buffer) { remote->cbs->unload_trace_buffer(desc, remote->priv); @@ -138,6 +139,21 @@ static int trace_remote_disable_tracing(struct trace_r= emote *remote) return 0; } =20 +static void trace_remote_reset(struct trace_remote *remote, int cpu) +{ + lockdep_assert_held(&remote->lock); + + if (!trace_remote_loaded(remote)) + return; + + if (cpu =3D=3D RING_BUFFER_ALL_CPUS) + ring_buffer_reset(remote->trace_buffer); + else + ring_buffer_reset_cpu(remote->trace_buffer, cpu); + + trace_remote_try_unload(remote); +} + static ssize_t tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, l= off_t *ppos) { @@ -414,6 +430,26 @@ static const struct file_operations trace_pipe_fops = =3D { .release =3D trace_pipe_release, }; =20 +static ssize_t trace_write(struct file *filp, const char __user *ubuf, siz= e_t cnt, loff_t *ppos) +{ + struct inode *inode =3D file_inode(filp); + struct trace_remote *remote =3D inode->i_private; + int cpu =3D RING_BUFFER_ALL_CPUS; + + if (inode->i_cdev) + cpu =3D (long)inode->i_cdev - 1; + + guard(mutex)(&remote->lock); + + trace_remote_reset(remote, cpu); + + return cnt; +} + +static const struct file_operations trace_fops =3D { + .write =3D trace_write, +}; + static int trace_remote_init_tracefs(const char *name, struct trace_remote= *remote) { struct dentry *remote_d, *percpu_d, *d; @@ -452,6 +488,10 @@ static int trace_remote_init_tracefs(const char *name,= struct trace_remote *remo if (!d) goto err; =20 + d =3D trace_create_file("trace", TRACEFS_MODE_WRITE, remote_d, remote, &t= race_fops); + if (!d) + goto err; + percpu_d =3D tracefs_create_dir("per_cpu", remote_d); if (!percpu_d) { pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name); @@ -474,6 +514,11 @@ static int trace_remote_init_tracefs(const char *name,= struct trace_remote *remo &trace_pipe_fops); if (!d) goto err; + + d =3D trace_create_cpu_file("trace", TRACEFS_MODE_WRITE, cpu_d, remote, = cpu, + &trace_fops); + if (!d) + goto err; } =20 return 0; --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0EA262F1FEA for ; 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dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AC/aIfdk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B68C8C2BCB1; Tue, 10 Mar 2026 14:35:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153353; bh=VPqMrxcxVoMI2KDxhrgzm9DCdic6WEPlXk97cknVgdY=; h=Date:From:To:Cc:Subject:References:From; b=AC/aIfdkHbk1xrW6Jl7BlaZjcOKky2sAroTDQ4qy+z4pFOgKR9468MFLBu3XKX/zR uGm7jV9YaUfgpCYCVOJFunCKlgmv7pFqXc7xrM3AJg1k/DBT0jgrznYU9q4rGRroDY VjNgXS8aJ6WyxrB97R3iuVhnFn0PN8b3CJjW5u3Et3VYEX8FoU5fqwP5nQvJB3YS+N z+3OAax7fJeWhH9ypUmXoD+IIdzlH2lbxbJUPnwdxmvXkz8Rev4jFL6hZt9pf+QO9/ HuP8sq0mNMHl0T2BwM0jQ+YFZT4KEgpAVBiH5SnMf5HvibFMICxUoQT0+954/k3iNH ezWDdce/EJqyw== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBn-00000002Zcm-3RTZ; Tue, 10 Mar 2026 10:36:03 -0400 Message-ID: <20260310143603.689651155@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:22 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 07/18] tracing: Add non-consuming read to trace remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Allow reading the trace file for trace remotes. This performs a non-consuming read of the trace buffer. Link: https://patch.msgid.link/20260309162516.2623589-8-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 2 +- kernel/trace/trace.h | 1 + kernel/trace/trace_remote.c | 339 ++++++++++++++++++++++++++++++++++-- 3 files changed, 326 insertions(+), 16 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index e33cb3c39f6e..5e1129b011cb 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3856,7 +3856,7 @@ static int s_show(struct seq_file *m, void *v) * Should be used after trace_array_get(), trace_types_lock * ensures that i_cdev was already initialized. */ -static inline int tracing_get_cpu(struct inode *inode) +int tracing_get_cpu(struct inode *inode) { if (inode->i_cdev) /* See trace_create_cpu_file() */ return (long)inode->i_cdev - 1; diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index d6af4405b341..fbbd0b2ee76f 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -695,6 +695,7 @@ struct dentry *trace_create_cpu_file(const char *name, void *data, long cpu, const struct file_operations *fops); +int tracing_get_cpu(struct inode *inode); =20 =20 /** diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index a7b94736dd38..039ba71c3b3e 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -18,14 +18,23 @@ #define TRACEFS_MODE_WRITE 0640 #define TRACEFS_MODE_READ 0440 =20 +enum tri_type { + TRI_CONSUMING, + TRI_NONCONSUMING, +}; + struct trace_remote_iterator { struct trace_remote *remote; struct trace_seq seq; struct delayed_work poll_work; unsigned long lost_events; u64 ts; + struct ring_buffer_iter *rb_iter; + struct ring_buffer_iter **rb_iters; int cpu; int evt_cpu; + loff_t pos; + enum tri_type type; }; =20 struct trace_remote { @@ -36,6 +45,8 @@ struct trace_remote { unsigned long trace_buffer_size; struct ring_buffer_remote rb_remote; struct mutex lock; + struct rw_semaphore reader_lock; + struct rw_semaphore *pcpu_reader_locks; unsigned int nr_readers; unsigned int poll_ms; bool tracing_on; @@ -230,6 +241,20 @@ static int trace_remote_get(struct trace_remote *remot= e, int cpu) if (ret) return ret; =20 + if (cpu !=3D RING_BUFFER_ALL_CPUS && !remote->pcpu_reader_locks) { + int lock_cpu; + + remote->pcpu_reader_locks =3D kcalloc(nr_cpu_ids, sizeof(*remote->pcpu_r= eader_locks), + GFP_KERNEL); + if (!remote->pcpu_reader_locks) { + trace_remote_try_unload(remote); + return -ENOMEM; + } + + for_each_possible_cpu(lock_cpu) + init_rwsem(&remote->pcpu_reader_locks[lock_cpu]); + } + remote->nr_readers++; =20 return 0; @@ -244,6 +269,9 @@ static void trace_remote_put(struct trace_remote *remot= e) if (remote->nr_readers) return; =20 + kfree(remote->pcpu_reader_locks); + remote->pcpu_reader_locks =3D NULL; + trace_remote_try_unload(remote); } =20 @@ -258,13 +286,55 @@ static void __poll_remote(struct work_struct *work) msecs_to_jiffies(iter->remote->poll_ms)); } =20 -static struct trace_remote_iterator *trace_remote_iter(struct trace_remote= *remote, int cpu) +static void __free_ring_buffer_iter(struct trace_remote_iterator *iter, in= t cpu) +{ + if (cpu !=3D RING_BUFFER_ALL_CPUS) { + ring_buffer_read_finish(iter->rb_iter); + return; + } + + for_each_possible_cpu(cpu) { + if (iter->rb_iters[cpu]) + ring_buffer_read_finish(iter->rb_iters[cpu]); + } + + kfree(iter->rb_iters); +} + +static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, in= t cpu) +{ + if (cpu !=3D RING_BUFFER_ALL_CPUS) { + iter->rb_iter =3D ring_buffer_read_start(iter->remote->trace_buffer, cpu= , GFP_KERNEL); + + return iter->rb_iter ? 0 : -ENOMEM; + } + + iter->rb_iters =3D kcalloc(nr_cpu_ids, sizeof(*iter->rb_iters), GFP_KERNE= L); + if (!iter->rb_iters) + return -ENOMEM; + + for_each_possible_cpu(cpu) { + iter->rb_iters[cpu] =3D ring_buffer_read_start(iter->remote->trace_buffe= r, cpu, + GFP_KERNEL); + if (!iter->rb_iters[cpu]) { + __free_ring_buffer_iter(iter, RING_BUFFER_ALL_CPUS); + return -ENOMEM; + } + } + + return 0; +} + +static struct trace_remote_iterator +*trace_remote_iter(struct trace_remote *remote, int cpu, enum tri_type typ= e) { struct trace_remote_iterator *iter =3D NULL; int ret; =20 lockdep_assert_held(&remote->lock); =20 + if (type =3D=3D TRI_NONCONSUMING && !trace_remote_loaded(remote)) + return NULL; =20 ret =3D trace_remote_get(remote, cpu); if (ret) @@ -279,9 +349,21 @@ static struct trace_remote_iterator *trace_remote_iter= (struct trace_remote *remo if (iter) { iter->remote =3D remote; iter->cpu =3D cpu; + iter->type =3D type; trace_seq_init(&iter->seq); - INIT_DELAYED_WORK(&iter->poll_work, __poll_remote); - schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms= )); + + switch (type) { + case TRI_CONSUMING: + INIT_DELAYED_WORK(&iter->poll_work, __poll_remote); + schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_m= s)); + break; + case TRI_NONCONSUMING: + ret =3D __alloc_ring_buffer_iter(iter, cpu); + break; + } + + if (ret) + goto err; =20 return iter; } @@ -305,10 +387,100 @@ static void trace_remote_iter_free(struct trace_remo= te_iterator *iter) =20 lockdep_assert_held(&remote->lock); =20 + switch (iter->type) { + case TRI_CONSUMING: + cancel_delayed_work_sync(&iter->poll_work); + break; + case TRI_NONCONSUMING: + __free_ring_buffer_iter(iter, iter->cpu); + break; + } + kfree(iter); trace_remote_put(remote); } =20 +static void trace_remote_iter_read_start(struct trace_remote_iterator *ite= r) +{ + struct trace_remote *remote =3D iter->remote; + int cpu =3D iter->cpu; + + /* Acquire global reader lock */ + if (cpu =3D=3D RING_BUFFER_ALL_CPUS && iter->type =3D=3D TRI_CONSUMING) + down_write(&remote->reader_lock); + else + down_read(&remote->reader_lock); + + if (cpu =3D=3D RING_BUFFER_ALL_CPUS) + return; + + /* + * No need for the remote lock here, iter holds a reference on + * remote->nr_readers + */ + + /* Get the per-CPU one */ + if (WARN_ON_ONCE(!remote->pcpu_reader_locks)) + return; + + if (iter->type =3D=3D TRI_CONSUMING) + down_write(&remote->pcpu_reader_locks[cpu]); + else + down_read(&remote->pcpu_reader_locks[cpu]); +} + +static void trace_remote_iter_read_finished(struct trace_remote_iterator *= iter) +{ + struct trace_remote *remote =3D iter->remote; + int cpu =3D iter->cpu; + + /* Release per-CPU reader lock */ + if (cpu !=3D RING_BUFFER_ALL_CPUS) { + /* + * No need for the remote lock here, iter holds a reference on + * remote->nr_readers + */ + if (iter->type =3D=3D TRI_CONSUMING) + up_write(&remote->pcpu_reader_locks[cpu]); + else + up_read(&remote->pcpu_reader_locks[cpu]); + } + + /* Release global reader lock */ + if (cpu =3D=3D RING_BUFFER_ALL_CPUS && iter->type =3D=3D TRI_CONSUMING) + up_write(&remote->reader_lock); + else + up_read(&remote->reader_lock); +} + +static struct ring_buffer_iter *__get_rb_iter(struct trace_remote_iterator= *iter, int cpu) +{ + return iter->cpu !=3D RING_BUFFER_ALL_CPUS ? iter->rb_iter : iter->rb_ite= rs[cpu]; +} + +static struct ring_buffer_event * +__peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigne= d long *lost_events) +{ + struct ring_buffer_event *rb_evt; + struct ring_buffer_iter *rb_iter; + + switch (iter->type) { + case TRI_CONSUMING: + return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events= ); + case TRI_NONCONSUMING: + rb_iter =3D __get_rb_iter(iter, cpu); + rb_evt =3D ring_buffer_iter_peek(rb_iter, ts); + if (!rb_evt) + return NULL; + + *lost_events =3D ring_buffer_iter_dropped(rb_iter); + + return rb_evt; + } + + return NULL; +} + static bool trace_remote_iter_read_event(struct trace_remote_iterator *ite= r) { struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; @@ -318,7 +490,7 @@ static bool trace_remote_iter_read_event(struct trace_r= emote_iterator *iter) if (ring_buffer_empty_cpu(trace_buffer, cpu)) return false; =20 - if (!ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events)) + if (!__peek_event(iter, cpu, &iter->ts, &iter->lost_events)) return false; =20 iter->evt_cpu =3D cpu; @@ -333,7 +505,7 @@ static bool trace_remote_iter_read_event(struct trace_r= emote_iterator *iter) if (ring_buffer_empty_cpu(trace_buffer, cpu)) continue; =20 - if (!ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events)) + if (!__peek_event(iter, cpu, &ts, &lost_events)) continue; =20 if (ts >=3D iter->ts) @@ -347,6 +519,20 @@ static bool trace_remote_iter_read_event(struct trace_= remote_iterator *iter) return iter->ts !=3D U64_MAX; } =20 +static void trace_remote_iter_move(struct trace_remote_iterator *iter) +{ + struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; + + switch (iter->type) { + case TRI_CONSUMING: + ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); + break; + case TRI_NONCONSUMING: + ring_buffer_iter_advance(__get_rb_iter(iter, iter->evt_cpu)); + break; + } +} + static int trace_remote_iter_print_event(struct trace_remote_iterator *ite= r) { unsigned long usecs_rem; @@ -369,13 +555,14 @@ static int trace_pipe_open(struct inode *inode, struc= t file *filp) { struct trace_remote *remote =3D inode->i_private; struct trace_remote_iterator *iter; - int cpu =3D RING_BUFFER_ALL_CPUS; - - if (inode->i_cdev) - cpu =3D (long)inode->i_cdev - 1; + int cpu =3D tracing_get_cpu(inode); =20 guard(mutex)(&remote->lock); - iter =3D trace_remote_iter(remote, cpu); + + iter =3D trace_remote_iter(remote, cpu, TRI_CONSUMING); + if (IS_ERR(iter)) + return PTR_ERR(iter); + filp->private_data =3D iter; =20 return IS_ERR(iter) ? PTR_ERR(iter) : 0; @@ -410,6 +597,8 @@ static ssize_t trace_pipe_read(struct file *filp, char = __user *ubuf, size_t cnt, if (ret < 0) return ret; =20 + trace_remote_iter_read_start(iter); + while (trace_remote_iter_read_event(iter)) { int prev_len =3D iter->seq.seq.len; =20 @@ -418,9 +607,11 @@ static ssize_t trace_pipe_read(struct file *filp, char= __user *ubuf, size_t cnt, break; } =20 - ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); + trace_remote_iter_move(iter); } =20 + trace_remote_iter_read_finished(iter); + goto copy_to_user; } =20 @@ -430,14 +621,127 @@ static const struct file_operations trace_pipe_fops = =3D { .release =3D trace_pipe_release, }; =20 +static void *trace_next(struct seq_file *m, void *v, loff_t *pos) +{ + struct trace_remote_iterator *iter =3D m->private; + + ++*pos; + + if (!iter || !trace_remote_iter_read_event(iter)) + return NULL; + + trace_remote_iter_move(iter); + iter->pos++; + + return iter; +} + +static void *trace_start(struct seq_file *m, loff_t *pos) +{ + struct trace_remote_iterator *iter =3D m->private; + loff_t i; + + if (!iter) + return NULL; + + trace_remote_iter_read_start(iter); + + if (!*pos) { + iter->pos =3D -1; + return trace_next(m, NULL, &i); + } + + i =3D iter->pos; + while (i < *pos) { + iter =3D trace_next(m, NULL, &i); + if (!iter) + return NULL; + } + + return iter; +} + +static int trace_show(struct seq_file *m, void *v) +{ + struct trace_remote_iterator *iter =3D v; + + trace_seq_init(&iter->seq); + + if (trace_remote_iter_print_event(iter)) { + seq_printf(m, "[EVENT %d PRINT TOO BIG]\n", iter->evt->id); + return 0; + } + + return trace_print_seq(m, &iter->seq); +} + +static void trace_stop(struct seq_file *m, void *v) +{ + struct trace_remote_iterator *iter =3D m->private; + + if (iter) + trace_remote_iter_read_finished(iter); +} + +static const struct seq_operations trace_sops =3D { + .start =3D trace_start, + .next =3D trace_next, + .show =3D trace_show, + .stop =3D trace_stop, +}; + +static int trace_open(struct inode *inode, struct file *filp) +{ + struct trace_remote *remote =3D inode->i_private; + struct trace_remote_iterator *iter =3D NULL; + int cpu =3D tracing_get_cpu(inode); + int ret; + + if (!(filp->f_mode & FMODE_READ)) + return 0; + + guard(mutex)(&remote->lock); + + iter =3D trace_remote_iter(remote, cpu, TRI_NONCONSUMING); + if (IS_ERR(iter)) + return PTR_ERR(iter); + + ret =3D seq_open(filp, &trace_sops); + if (ret) { + trace_remote_iter_free(iter); + return ret; + } + + ((struct seq_file *)filp->private_data)->private =3D (void *)iter; + + return 0; +} + +static int trace_release(struct inode *inode, struct file *filp) +{ + struct trace_remote_iterator *iter; + + if (!(filp->f_mode & FMODE_READ)) + return 0; + + iter =3D ((struct seq_file *)filp->private_data)->private; + seq_release(inode, filp); + + if (!iter) + return 0; + + guard(mutex)(&iter->remote->lock); + + trace_remote_iter_free(iter); + + return 0; +} + static ssize_t trace_write(struct file *filp, const char __user *ubuf, siz= e_t cnt, loff_t *ppos) { struct inode *inode =3D file_inode(filp); struct trace_remote *remote =3D inode->i_private; 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charset="utf-8" From: Vincent Donnefort Add a .init call back so the trace remote callers can add entries to the tracefs directory. Link: https://patch.msgid.link/20260309162516.2623589-9-vdonnefort@google.c= om Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/trace_remote.h | 4 ++++ kernel/trace/trace_remote.c | 7 ++++++- 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h index 10ca03dc192b..090c58b7d92b 100644 --- a/include/linux/trace_remote.h +++ b/include/linux/trace_remote.h @@ -3,10 +3,13 @@ #ifndef _LINUX_TRACE_REMOTE_H #define _LINUX_TRACE_REMOTE_H =20 +#include #include =20 /** * struct trace_remote_callbacks - Callbacks used by Tracefs to control th= e remote + * @init: Called once the remote has been registered. Allows the + * caller to extend the Tracefs remote directory * @load_trace_buffer: Called before Tracefs accesses the trace buffer fo= r the first * time. Must return a &trace_buffer_desc * (most likely filled with trace_remote_alloc_buffer()) @@ -22,6 +25,7 @@ * new reader-page from the @cpu ring-buffer. */ struct trace_remote_callbacks { + int (*init)(struct dentry *d, void *priv); struct trace_buffer_desc *(*load_trace_buffer)(unsigned long size, void *= priv); void (*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv); int (*enable_tracing)(bool enable, void *priv); diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 039ba71c3b3e..294d051dcef1 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -863,6 +863,7 @@ static int trace_remote_init_tracefs(const char *name, = struct trace_remote *remo int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv) { struct trace_remote *remote; + int ret; =20 remote =3D kzalloc_obj(*remote); if (!remote) @@ -880,7 +881,11 @@ int trace_remote_register(const char *name, struct tra= ce_remote_callbacks *cbs, return -ENOMEM; } =20 - return 0; + ret =3D cbs->init ? cbs->init(remote->dentry, priv) : 0; + if (ret) + pr_err("Init failed for trace remote '%s' (%d)\n", name, ret); + + return ret; } EXPORT_SYMBOL_GPL(trace_remote_register); =20 --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 33FE82F3C0E for ; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; cv=none; b=FsGu9hxf9bWaGoNSVMcyJIpWj0tLHg33x0FXNr4mie7RNq5Obs2911F+DJwKjH29XHweLL8myj2nmITLCPcEdV5F+X9qr4FnOvwaEX5R9UUMP3ps4JVIeCL0YdNV6rZ7ICPPGSZizexWeaV5dP1+eYA1Be4DSab2Rno4FwG1YW8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; c=relaxed/simple; bh=m+AXGtGr9Wc0yOUUD88NFqcn26FV9ZVrr9knxPb4/qk=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=ZTa+mgF4Mpo+Wi4eGT/IObU+8B9JqkSnX/F37RwIZy07WbESK8+SSOlTnD/Dg3Ckuq6fizyaERk6dRO92JKwyClg3oapvjZuiNLcPOvZFaTYy442SOKWuIoyF5d8G8gej+/L2s6aLMAqILrvVQ+M2vBJgUIzNXw/SIHKnX4m79k= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XW+Kgz0H; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XW+Kgz0H" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07200C2BCB3; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153354; bh=m+AXGtGr9Wc0yOUUD88NFqcn26FV9ZVrr9knxPb4/qk=; h=Date:From:To:Cc:Subject:References:From; b=XW+Kgz0HiCLq6ZpdBKH+P+OKyPVpIZAA1hw5H4QvDyP3AD/iGw1Oc2PEj12u1axCu 2nYxDClgUsB4WytU5WxQnEEeZWzmPp06SNXSH0SgVraElfgIb2+wSYy3nVL0m4ZFV3 JWnK7YDsHGQRiyYHmD+IfYD6GOx1dMs2RHKQejcG4zO7iJdF5et5AWZ8V045z39Kgm DWrprbmzzT/h0yy2ESJfUUF+qzdB+ChwJSIfmJMfhyUJT8rt5ZCl0MJ0oWJrr9TCkT Q+ET3yDgCE9333VhQ6EV7ed5lDv+/2MfaLMAsT0VUjqr9891cxO9alKOwgRvpxP3tH dWt2UMFhddRHw== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBo-00000002Zdm-0Va2; Tue, 10 Mar 2026 10:36:04 -0400 Message-ID: <20260310143603.983354111@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:24 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 09/18] tracing: Add events to trace remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort An event is predefined point in the writer code that allows to log data. Following the same scheme as kernel events, add remote events, described to user-space within the events/ tracefs directory found in the corresponding trace remote. Remote events are expected to be described during the trace remote registration. Add also a .enable_event callback for trace_remote to toggle the event logging, if supported. Link: https://patch.msgid.link/20260309162516.2623589-10-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/trace_remote.h | 7 +- include/linux/trace_remote_event.h | 23 +++ kernel/trace/trace_remote.c | 264 ++++++++++++++++++++++++++++- 3 files changed, 288 insertions(+), 6 deletions(-) create mode 100644 include/linux/trace_remote_event.h diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h index 090c58b7d92b..fcd1d46ea466 100644 --- a/include/linux/trace_remote.h +++ b/include/linux/trace_remote.h @@ -5,6 +5,7 @@ =20 #include #include +#include =20 /** * struct trace_remote_callbacks - Callbacks used by Tracefs to control th= e remote @@ -23,6 +24,8 @@ * @reset: Called on `echo 0 > trace`. It is expected from the * remote to reset all ring-buffer pages. * new reader-page from the @cpu ring-buffer. + * @enable_event: Called on events/event_name/enable. It is expected from + * the remote to allow the writing event @id. */ struct trace_remote_callbacks { int (*init)(struct dentry *d, void *priv); @@ -31,9 +34,11 @@ struct trace_remote_callbacks { int (*enable_tracing)(bool enable, void *priv); int (*swap_reader_page)(unsigned int cpu, void *priv); int (*reset)(unsigned int cpu, void *priv); + int (*enable_event)(unsigned short id, bool enable, void *priv); }; =20 -int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv); +int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv, + struct remote_event *events, size_t nr_events); =20 int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_= size, size_t buffer_size, const struct cpumask *cpumask); diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remot= e_event.h new file mode 100644 index 000000000000..a4449008a075 --- /dev/null +++ b/include/linux/trace_remote_event.h @@ -0,0 +1,23 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _LINUX_TRACE_REMOTE_EVENTS_H +#define _LINUX_TRACE_REMOTE_EVENTS_H + +struct trace_remote; +struct trace_event_fields; + +struct remote_event_hdr { + unsigned short id; +}; + +#define REMOTE_EVENT_NAME_MAX 30 +struct remote_event { + char name[REMOTE_EVENT_NAME_MAX]; + unsigned short id; + bool enabled; + struct trace_remote *remote; + struct trace_event_fields *fields; + char *print_fmt; + void (*print)(void *evt, struct trace_seq *seq); +}; +#endif diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 294d051dcef1..0d0af53c0ce9 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -31,6 +31,7 @@ struct trace_remote_iterator { u64 ts; struct ring_buffer_iter *rb_iter; struct ring_buffer_iter **rb_iters; + struct remote_event_hdr *evt; int cpu; int evt_cpu; loff_t pos; @@ -42,6 +43,10 @@ struct trace_remote { void *priv; struct trace_buffer *trace_buffer; struct trace_buffer_desc *trace_buffer_desc; + struct dentry *dentry; + struct eventfs_inode *eventfs; + struct remote_event *events; + unsigned long nr_events; unsigned long trace_buffer_size; struct ring_buffer_remote rb_remote; struct mutex lock; @@ -168,7 +173,8 @@ static void trace_remote_reset(struct trace_remote *rem= ote, int cpu) static ssize_t tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, l= off_t *ppos) { - struct trace_remote *remote =3D filp->private_data; + struct seq_file *seq =3D filp->private_data; + struct trace_remote *remote =3D seq->private; unsigned long val; int ret; =20 @@ -197,7 +203,8 @@ DEFINE_SHOW_STORE_ATTRIBUTE(tracing_on); static ssize_t buffer_size_kb_write(struct file *filp, const char __user *= ubuf, size_t cnt, loff_t *ppos) { - struct trace_remote *remote =3D filp->private_data; + struct seq_file *seq =3D filp->private_data; + struct trace_remote *remote =3D seq->private; unsigned long val; int ret; =20 @@ -484,16 +491,19 @@ __peek_event(struct trace_remote_iterator *iter, int = cpu, u64 *ts, unsigned long static bool trace_remote_iter_read_event(struct trace_remote_iterator *ite= r) { struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; + struct ring_buffer_event *rb_evt; int cpu =3D iter->cpu; =20 if (cpu !=3D RING_BUFFER_ALL_CPUS) { if (ring_buffer_empty_cpu(trace_buffer, cpu)) return false; =20 - if (!__peek_event(iter, cpu, &iter->ts, &iter->lost_events)) + rb_evt =3D __peek_event(iter, cpu, &iter->ts, &iter->lost_events); + if (!rb_evt) return false; =20 iter->evt_cpu =3D cpu; + iter->evt =3D ring_buffer_event_data(rb_evt); return true; } =20 @@ -505,7 +515,8 @@ static bool trace_remote_iter_read_event(struct trace_r= emote_iterator *iter) if (ring_buffer_empty_cpu(trace_buffer, cpu)) continue; =20 - if (!__peek_event(iter, cpu, &ts, &lost_events)) + rb_evt =3D __peek_event(iter, cpu, &ts, &lost_events); + if (!rb_evt) continue; =20 if (ts >=3D iter->ts) @@ -513,6 +524,7 @@ static bool trace_remote_iter_read_event(struct trace_r= emote_iterator *iter) =20 iter->ts =3D ts; iter->evt_cpu =3D cpu; + iter->evt =3D ring_buffer_event_data(rb_evt); iter->lost_events =3D lost_events; } =20 @@ -533,8 +545,11 @@ static void trace_remote_iter_move(struct trace_remote= _iterator *iter) } } =20 +static struct remote_event *trace_remote_find_event(struct trace_remote *r= emote, unsigned short id); + static int trace_remote_iter_print_event(struct trace_remote_iterator *ite= r) { + struct remote_event *evt; unsigned long usecs_rem; u64 ts =3D iter->ts; =20 @@ -548,6 +563,12 @@ static int trace_remote_iter_print_event(struct trace_= remote_iterator *iter) trace_seq_printf(&iter->seq, "[%03d]\t%5llu.%06lu: ", iter->evt_cpu, ts, usecs_rem); =20 + evt =3D trace_remote_find_event(iter->remote, iter->evt->id); + if (!evt) + trace_seq_printf(&iter->seq, "UNKNOWN id=3D%d\n", iter->evt->id); + else + evt->print(iter->evt, &iter->seq); + return trace_seq_has_overflowed(&iter->seq) ? -EOVERFLOW : 0; } =20 @@ -829,6 +850,8 @@ static int trace_remote_init_tracefs(const char *name, = struct trace_remote *remo goto err; } =20 + remote->dentry =3D remote_d; + return 0; =20 err: @@ -842,6 +865,9 @@ static int trace_remote_init_tracefs(const char *name, = struct trace_remote *remo return -ENOMEM; } =20 +static int trace_remote_register_events(const char *remote_name, struct tr= ace_remote *remote, + struct remote_event *events, size_t nr_events); + /** * trace_remote_register() - Register a Tracefs remote * @name: Name of the remote, used for the Tracefs remotes/ directory. @@ -860,7 +886,8 @@ static int trace_remote_init_tracefs(const char *name, = struct trace_remote *remo * * Return: 0 on success, negative error code on failure. */ -int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv) +int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv, + struct remote_event *events, size_t nr_events) { struct trace_remote *remote; int ret; @@ -881,6 +908,13 @@ int trace_remote_register(const char *name, struct tra= ce_remote_callbacks *cbs, return -ENOMEM; } =20 + ret =3D trace_remote_register_events(name, remote, events, nr_events); + if (ret) { + pr_err("Failed to register events for trace remote '%s' (%d)\n", + name, ret); + return ret; + } + ret =3D cbs->init ? cbs->init(remote->dentry, priv) : 0; if (ret) pr_err("Init failed for trace remote '%s' (%d)\n", name, ret); @@ -976,3 +1010,223 @@ int trace_remote_alloc_buffer(struct trace_buffer_de= sc *desc, size_t desc_size, return ret; } EXPORT_SYMBOL_GPL(trace_remote_alloc_buffer); + +static int +trace_remote_enable_event(struct trace_remote *remote, struct remote_event= *evt, bool enable) +{ + int ret; + + lockdep_assert_held(&remote->lock); + + if (evt->enabled =3D=3D enable) + return 0; + + ret =3D remote->cbs->enable_event(evt->id, enable, remote->priv); + if (ret) + return ret; + + evt->enabled =3D enable; + + return 0; +} + +static int remote_event_enable_show(struct seq_file *s, void *unused) +{ + struct remote_event *evt =3D s->private; + + seq_printf(s, "%d\n", evt->enabled); + + return 0; +} + +static ssize_t remote_event_enable_write(struct file *filp, const char __u= ser *ubuf, + size_t count, loff_t *ppos) +{ + struct seq_file *seq =3D filp->private_data; + struct remote_event *evt =3D seq->private; + struct trace_remote *remote =3D evt->remote; + u8 enable; + int ret; + + ret =3D kstrtou8_from_user(ubuf, count, 10, &enable); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + ret =3D trace_remote_enable_event(remote, evt, enable); + if (ret) + return ret; + + return count; +} +DEFINE_SHOW_STORE_ATTRIBUTE(remote_event_enable); + +static int remote_event_id_show(struct seq_file *s, void *unused) +{ + struct remote_event *evt =3D s->private; + + seq_printf(s, "%d\n", evt->id); + + return 0; +} +DEFINE_SHOW_ATTRIBUTE(remote_event_id); + +static int remote_event_format_show(struct seq_file *s, void *unused) +{ + size_t offset =3D sizeof(struct remote_event_hdr); + struct remote_event *evt =3D s->private; + struct trace_event_fields *field; + + seq_printf(s, "name: %s\n", evt->name); + seq_printf(s, "ID: %d\n", evt->id); + seq_puts(s, + "format:\n\tfield:unsigned short common_type;\toffset:0;\tsize:2;\tsign= ed:0;\n\n"); + + field =3D &evt->fields[0]; + while (field->name) { + seq_printf(s, "\tfield:%s %s;\toffset:%zu;\tsize:%u;\tsigned:%d;\n", + field->type, field->name, offset, field->size, + field->is_signed); + offset +=3D field->size; + field++; + } + + if (field !=3D &evt->fields[0]) + seq_puts(s, "\n"); + + seq_printf(s, "print fmt: %s\n", evt->print_fmt); + + return 0; +} +DEFINE_SHOW_ATTRIBUTE(remote_event_format); + +static int remote_event_callback(const char *name, umode_t *mode, void **d= ata, + const struct file_operations **fops) +{ + if (!strcmp(name, "enable")) { + *mode =3D TRACEFS_MODE_WRITE; + *fops =3D &remote_event_enable_fops; + return 1; + } + + if (!strcmp(name, "id")) { + *mode =3D TRACEFS_MODE_READ; + *fops =3D &remote_event_id_fops; + return 1; + } + + if (!strcmp(name, "format")) { + *mode =3D TRACEFS_MODE_READ; + *fops =3D &remote_event_format_fops; + return 1; + } + + return 0; +} + +static int trace_remote_init_eventfs(const char *remote_name, struct trace= _remote *remote, + struct remote_event *evt) +{ + struct eventfs_inode *eventfs =3D remote->eventfs; + static struct eventfs_entry entries[] =3D { + { + .name =3D "enable", + .callback =3D remote_event_callback, + }, { + .name =3D "id", + .callback =3D remote_event_callback, + }, { + .name =3D "format", + .callback =3D remote_event_callback, + } + }; + bool eventfs_create =3D false; + + if (!eventfs) { + eventfs =3D eventfs_create_events_dir("events", remote->dentry, NULL, 0,= NULL); + if (IS_ERR(eventfs)) + return PTR_ERR(eventfs); + + /* + * Create similar hierarchy as local events even if a single system is s= upported at + * the moment + */ + eventfs =3D eventfs_create_dir(remote_name, eventfs, NULL, 0, NULL); + if (IS_ERR(eventfs)) + return PTR_ERR(eventfs); + + remote->eventfs =3D eventfs; + eventfs_create =3D true; + } + + eventfs =3D eventfs_create_dir(evt->name, eventfs, entries, ARRAY_SIZE(en= tries), evt); + if (IS_ERR(eventfs)) { + if (eventfs_create) { + eventfs_remove_events_dir(remote->eventfs); + remote->eventfs =3D NULL; + } + return PTR_ERR(eventfs); + } + + return 0; +} + +static int trace_remote_attach_events(struct trace_remote *remote, struct = remote_event *events, + size_t nr_events) +{ + int i; + + for (i =3D 0; i < nr_events; i++) { + struct remote_event *evt =3D &events[i]; + + if (evt->remote) + return -EEXIST; + + evt->remote =3D remote; + + /* We need events to be sorted for efficient lookup */ + if (i && evt->id <=3D events[i - 1].id) + return -EINVAL; + } + + remote->events =3D events; + remote->nr_events =3D nr_events; + + return 0; +} + +static int trace_remote_register_events(const char *remote_name, struct tr= ace_remote *remote, + struct remote_event *events, size_t nr_events) +{ + int i, ret; + + ret =3D trace_remote_attach_events(remote, events, nr_events); + if (ret) + return ret; + + for (i =3D 0; i < nr_events; i++) { + struct remote_event *evt =3D &events[i]; + + ret =3D trace_remote_init_eventfs(remote_name, remote, evt); + if (ret) + pr_warn("Failed to init eventfs for event '%s' (%d)", + evt->name, ret); + } + + return 0; +} + +static int __cmp_events(const void *key, const void *data) +{ + const struct remote_event *evt =3D data; + int id =3D (int)((long)key); + + return id - (int)evt->id; +} + +static struct remote_event *trace_remote_find_event(struct trace_remote *r= emote, unsigned short id) +{ + return bsearch((const void *)(unsigned long)id, remote->events, remote->n= r_events, + sizeof(*remote->events), __cmp_events); 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Tue, 10 Mar 2026 10:36:04 -0400 Message-ID: <20260310143604.136215492@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:25 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 10/18] tracing: Add events/ root files to trace remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Just like for the kernel events directory, add 'enable', 'header_page' and 'header_event' at the root of the trace remote events/ directory. Link: https://patch.msgid.link/20260309162516.2623589-11-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 3 +- kernel/trace/trace_remote.c | 138 +++++++++++++++++++++++++++++++++++- 2 files changed, 139 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index fb39dd43e00b..605142e06863 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -640,7 +640,8 @@ int ring_buffer_print_page_header(struct trace_buffer *= buffer, struct trace_seq trace_seq_printf(s, "\tfield: char data;\t" "offset:%u;\tsize:%u;\tsigned:%u;\n", (unsigned int)offsetof(typeof(field), data), - (unsigned int)buffer->subbuf_size, + (unsigned int)(buffer ? buffer->subbuf_size : + PAGE_SIZE - BUF_PAGE_HDR_SIZE), (unsigned int)is_signed_type(char)); =20 return !trace_seq_has_overflowed(s); diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 0d0af53c0ce9..0d78e5f5fe98 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -1125,10 +1125,145 @@ static int remote_event_callback(const char *name,= umode_t *mode, void **data, return 0; } =20 +static ssize_t remote_events_dir_enable_write(struct file *filp, const cha= r __user *ubuf, + size_t count, loff_t *ppos) +{ + struct trace_remote *remote =3D file_inode(filp)->i_private; + int i, ret; + u8 enable; + + ret =3D kstrtou8_from_user(ubuf, count, 10, &enable); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + for (i =3D 0; i < remote->nr_events; i++) { + struct remote_event *evt =3D &remote->events[i]; + + trace_remote_enable_event(remote, evt, enable); + } + + return count; +} + +static ssize_t remote_events_dir_enable_read(struct file *filp, char __use= r *ubuf, size_t cnt, + loff_t *ppos) +{ + struct trace_remote *remote =3D file_inode(filp)->i_private; + const char enabled_char[] =3D {'0', '1', 'X'}; + char enabled_str[] =3D " \n"; + int i, enabled =3D -1; + + guard(mutex)(&remote->lock); + + for (i =3D 0; i < remote->nr_events; i++) { + struct remote_event *evt =3D &remote->events[i]; + + if (enabled =3D=3D -1) { + enabled =3D evt->enabled; + } else if (enabled !=3D evt->enabled) { + enabled =3D 2; + break; + } + } + + enabled_str[0] =3D enabled_char[enabled =3D=3D -1 ? 0 : enabled]; + + return simple_read_from_buffer(ubuf, cnt, ppos, enabled_str, 2); +} + +static const struct file_operations remote_events_dir_enable_fops =3D { + .write =3D remote_events_dir_enable_write, + .read =3D remote_events_dir_enable_read, +}; + +static ssize_t +remote_events_dir_header_page_read(struct file *filp, char __user *ubuf, s= ize_t cnt, loff_t *ppos) +{ + struct trace_seq *s; + int ret; + + s =3D kmalloc(sizeof(*s), GFP_KERNEL); + if (!s) + return -ENOMEM; + + trace_seq_init(s); + + ring_buffer_print_page_header(NULL, s); + ret =3D simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, trace_seq_use= d(s)); + kfree(s); + + return ret; +} + +static const struct file_operations remote_events_dir_header_page_fops =3D= { + .read =3D remote_events_dir_header_page_read, +}; + +static ssize_t +remote_events_dir_header_event_read(struct file *filp, char __user *ubuf, = size_t cnt, loff_t *ppos) +{ + struct trace_seq *s; + int ret; + + s =3D kmalloc(sizeof(*s), GFP_KERNEL); + if (!s) + return -ENOMEM; + + trace_seq_init(s); + + ring_buffer_print_entry_header(s); + ret =3D simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, trace_seq_use= d(s)); + kfree(s); + + return ret; +} + +static const struct file_operations remote_events_dir_header_event_fops = =3D { + .read =3D remote_events_dir_header_event_read, +}; + +static int remote_events_dir_callback(const char *name, umode_t *mode, voi= d **data, + const struct file_operations **fops) +{ + if (!strcmp(name, "enable")) { + *mode =3D TRACEFS_MODE_WRITE; + *fops =3D &remote_events_dir_enable_fops; + return 1; + } + + if (!strcmp(name, "header_page")) { + *mode =3D TRACEFS_MODE_READ; + *fops =3D &remote_events_dir_header_page_fops; + return 1; + } + + if (!strcmp(name, "header_event")) { + *mode =3D TRACEFS_MODE_READ; + *fops =3D &remote_events_dir_header_event_fops; + return 1; + } + + return 0; +} + static int trace_remote_init_eventfs(const char *remote_name, struct trace= _remote *remote, struct remote_event *evt) { struct eventfs_inode *eventfs =3D remote->eventfs; + static struct eventfs_entry dir_entries[] =3D { + { + .name =3D "enable", + .callback =3D remote_events_dir_callback, + }, { + .name =3D "header_page", + .callback =3D remote_events_dir_callback, + }, { + .name =3D "header_event", + .callback =3D remote_events_dir_callback, + } + }; static struct eventfs_entry entries[] =3D { { .name =3D "enable", @@ -1144,7 +1279,8 @@ static int trace_remote_init_eventfs(const char *remo= te_name, struct trace_remot bool eventfs_create =3D false; =20 if (!eventfs) { - eventfs =3D eventfs_create_events_dir("events", remote->dentry, NULL, 0,= NULL); + eventfs =3D eventfs_create_events_dir("events", remote->dentry, dir_entr= ies, + ARRAY_SIZE(dir_entries), remote); if (IS_ERR(eventfs)) return PTR_ERR(eventfs); =20 --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 61FE82D63F8 for ; 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charset="utf-8" From: Vincent Donnefort Declaring remote events can be cumbersome let's add a set of macros to simplify developers life. The declaration of a remote event is very similar to kernel's events: REMOTE_EVENT(name, id, RE_STRUCT( re_field(u64 foo) ), RE_PRINTK("foo=3D%llu", __entry->foo) ) Link: https://patch.msgid.link/20260309162516.2623589-12-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/trace_remote_event.h | 10 ++++ include/trace/define_remote_events.h | 73 ++++++++++++++++++++++++++++ 2 files changed, 83 insertions(+) create mode 100644 include/trace/define_remote_events.h diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remot= e_event.h index a4449008a075..c8ae1e1f5e72 100644 --- a/include/linux/trace_remote_event.h +++ b/include/linux/trace_remote_event.h @@ -5,6 +5,7 @@ =20 struct trace_remote; struct trace_event_fields; +struct trace_seq; =20 struct remote_event_hdr { unsigned short id; @@ -20,4 +21,13 @@ struct remote_event { char *print_fmt; void (*print)(void *evt, struct trace_seq *seq); }; + +#define RE_STRUCT(__args...) __args +#define re_field(__type, __field) __type __field; + +#define REMOTE_EVENT_FORMAT(__name, __struct) \ + struct remote_event_format_##__name { \ + struct remote_event_hdr hdr; \ + __struct \ + } #endif diff --git a/include/trace/define_remote_events.h b/include/trace/define_re= mote_events.h new file mode 100644 index 000000000000..676e803dc144 --- /dev/null +++ b/include/trace/define_remote_events.h @@ -0,0 +1,73 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include +#include +#include +#include + +#define REMOTE_EVENT_INCLUDE(__file) __stringify(../../__file) + +#ifdef REMOTE_EVENT_SECTION +# define __REMOTE_EVENT_SECTION(__name) __used __section(REMOTE_EVENT_SECT= ION"."#__name) +#else +# define __REMOTE_EVENT_SECTION(__name) +#endif + +#define REMOTE_PRINTK_COUNT_ARGS(__args...) \ + __COUNT_ARGS(, ##__args, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0) + +#define __remote_printk0() \ + trace_seq_putc(seq, '\n') + +#define __remote_printk1(__fmt) \ + trace_seq_puts(seq, " " __fmt "\n") \ + +#define __remote_printk2(__fmt, __args...) \ +do { \ + trace_seq_putc(seq, ' '); \ + trace_seq_printf(seq, __fmt, __args); \ + trace_seq_putc(seq, '\n'); \ +} while (0) + +/* Apply the appropriate trace_seq sequence according to the number of arg= uments */ +#define remote_printk(__args...) \ + CONCATENATE(__remote_printk, REMOTE_PRINTK_COUNT_ARGS(__args))(__args) + +#define RE_PRINTK(__args...) __args + +#define REMOTE_EVENT(__name, __id, __struct, __printk) \ + REMOTE_EVENT_FORMAT(__name, __struct); \ + static void remote_event_print_##__name(void *evt, struct trace_seq *seq)= \ + { \ + struct remote_event_format_##__name __maybe_unused *__entry =3D evt; \ + trace_seq_puts(seq, #__name); \ + remote_printk(__printk); \ + } +#include REMOTE_EVENT_INCLUDE(REMOTE_EVENT_INCLUDE_FILE) + +#undef REMOTE_EVENT +#undef RE_PRINTK +#undef re_field +#define re_field(__type, __field) \ + { \ + .type =3D #__type, .name =3D #__field, \ + .size =3D sizeof(__type), .align =3D __alignof__(__type), \ + .is_signed =3D is_signed_type(__type), \ + }, +#define __entry REC +#define RE_PRINTK(__fmt, __args...) "\"" __fmt "\", " __stringify(__args) +#define REMOTE_EVENT(__name, __id, __struct, __printk) \ + static struct trace_event_fields remote_event_fields_##__name[] =3D { \ + __struct \ + {} \ + }; \ + static char remote_event_print_fmt_##__name[] =3D __printk; \ + static struct remote_event __REMOTE_EVENT_SECTION(__name) \ + remote_event_##__name =3D { \ + .name =3D #__name, \ + .id =3D __id, \ + .fields =3D remote_event_fields_##__name, \ + .print_fmt =3D remote_event_print_fmt_##__name, \ + .print =3D remote_event_print_##__name, \ + } +#include REMOTE_EVENT_INCLUDE(REMOTE_EVENT_INCLUDE_FILE) --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8EF523033D6 for ; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; cv=none; b=Z4F0tRCvB64H00pioaCPt6uTXm01Q9LzqDnO39Mawyb/5/dlB/LNA9yRn4g+49dD5d8S5gRcAVmcPrHw77ZNtRIkfCnER5o0YlYvKrCKyGE6z3gN41K23L5mpyEEbvi3OX9P3BsGMOsHXBdmJsHelNIfCmQ6ZBkpb5GWPitOch0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; c=relaxed/simple; bh=80QQt/aOJwthIgq4lmCocvnrAhE5jyJJkbaXJl2Vxnw=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=r0j479sP0iYxxRgpeChGDD4UNNeJ29NjdNKG/9OLtd4Kk/vjIRv5l0sddzNHL35P9lEq0jZMVKIhqqw1DlsbstFVBS7iLucoUO91bA3pkQdXCP5vJ7/LLBVokITJRkcJrvTtHK55NrIm1tudRBhdlcgUU/fbT8MvbJTI//92RGs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ufbSdoyk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ufbSdoyk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71EE1C19423; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153354; bh=80QQt/aOJwthIgq4lmCocvnrAhE5jyJJkbaXJl2Vxnw=; h=Date:From:To:Cc:Subject:References:From; b=ufbSdoyk5XwFLPAJF0QaeOb8MdqD1nYC0+OpCSz+GQj9teBJstcUiqw9nVU8h4H1a l6Q2iZmkHlLYnJ8LYOPwutOhTdxUFlvOaYb8lsZMzD6CW5BuEaVugtWnTrEWsfEyVH 5Xi30KddB6btA7NnfoKpOYqRzAZeKlCt3IJx7rdWD/mSqkwCnocYNMIhpZ0VLPAhYH Nix6aHYdQ7CtOm4IYyKD2XvNRsoGecjTRzQJ6NsuMrtpFpbyMN8zhyxhPp4TOcEQ7N J1/Y4TKb2w9v8jYPBZe7TWw3+kuZpwtA/ax6Uh3HEpoc7g0LZ4at3DnazDalGzJZYv 01ZrO9vXU9Hpw== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBo-00000002ZfH-2L4Z; Tue, 10 Mar 2026 10:36:04 -0400 Message-ID: <20260310143604.435316731@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:27 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 12/18] ring-buffer: Export buffer_data_page and macros References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort In preparation for allowing the writing of ring-buffer compliant pages outside of ring_buffer.c, move buffer_data_page and timestamps encoding macros into the publicly available ring_buffer_types.h. Link: https://patch.msgid.link/20260309162516.2623589-13-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/ring_buffer_types.h | 41 +++++++++++++++++++++++++++++++ kernel/trace/ring_buffer.c | 36 +-------------------------- 2 files changed, 42 insertions(+), 35 deletions(-) create mode 100644 include/linux/ring_buffer_types.h diff --git a/include/linux/ring_buffer_types.h b/include/linux/ring_buffer_= types.h new file mode 100644 index 000000000000..54577021a49d --- /dev/null +++ b/include/linux/ring_buffer_types.h @@ -0,0 +1,41 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_RING_BUFFER_TYPES_H +#define _LINUX_RING_BUFFER_TYPES_H + +#include + +#define TS_SHIFT 27 +#define TS_MASK ((1ULL << TS_SHIFT) - 1) +#define TS_DELTA_TEST (~TS_MASK) + +/* + * We need to fit the time_stamp delta into 27 bits. + */ +static inline bool test_time_stamp(u64 delta) +{ + return !!(delta & TS_DELTA_TEST); +} + +#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data) + +#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array)) +#define RB_ALIGNMENT 4U +#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX) +#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */ + +#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS +# define RB_FORCE_8BYTE_ALIGNMENT 0 +# define RB_ARCH_ALIGNMENT RB_ALIGNMENT +#else +# define RB_FORCE_8BYTE_ALIGNMENT 1 +# define RB_ARCH_ALIGNMENT 8U +#endif + +#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT) + +struct buffer_data_page { + u64 time_stamp; /* page time stamp */ + local_t commit; /* write committed index */ + unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */ +}; +#endif diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 605142e06863..96e0d80d492b 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4,6 +4,7 @@ * * Copyright (C) 2008 Steven Rostedt */ +#include #include #include #include @@ -157,23 +158,6 @@ int ring_buffer_print_entry_header(struct trace_seq *s) /* Used for individual buffers (after the counter) */ #define RB_BUFFER_OFF (1 << 20) =20 -#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data) - -#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array)) -#define RB_ALIGNMENT 4U -#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX) -#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */ - -#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS -# define RB_FORCE_8BYTE_ALIGNMENT 0 -# define RB_ARCH_ALIGNMENT RB_ALIGNMENT -#else -# define RB_FORCE_8BYTE_ALIGNMENT 1 -# define RB_ARCH_ALIGNMENT 8U -#endif - -#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT) - /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */ #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX =20 @@ -316,10 +300,6 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data); #define for_each_online_buffer_cpu(buffer, cpu) \ for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask) =20 -#define TS_SHIFT 27 -#define TS_MASK ((1ULL << TS_SHIFT) - 1) -#define TS_DELTA_TEST (~TS_MASK) - static u64 rb_event_time_stamp(struct ring_buffer_event *event) { u64 ts; @@ -338,12 +318,6 @@ static u64 rb_event_time_stamp(struct ring_buffer_even= t *event) =20 #define RB_MISSED_MASK (3 << 30) =20 -struct buffer_data_page { - u64 time_stamp; /* page time stamp */ - local_t commit; /* write committed index */ - unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */ -}; - struct buffer_data_read_page { unsigned order; /* order of the page */ struct buffer_data_page *data; /* actual data, stored in this page */ @@ -437,14 +411,6 @@ static struct buffer_data_page *alloc_cpu_data(int cpu= , int order) return dpage; } =20 -/* - * We need to fit the time_stamp delta into 27 bits. - */ -static inline bool test_time_stamp(u64 delta) -{ - return !!(delta & TS_DELTA_TEST); -} - struct rb_irq_work { struct irq_work work; wait_queue_head_t waiters; --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D30293033FE for ; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; cv=none; b=jJ6xFDNJni1t4n8o11r6YNIPXdrwzu71W1MTfQfTE+KeCH6De9cLcyjrlhqrwCo/wthJqWpG7Do2QJXTofOYoauPh8ZJYy04TlwQWbcV1sSvyu3j8BPKNCiDmPUyJuJkeWBcsNDvrrFQmcXhkjfguq1zVbgjdCZaVjS4PYgbPko= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; c=relaxed/simple; bh=pxqba9wmZxQ1nmSRgyrt1Z9u0BBfiTIH8Z8HAWwBMIY=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=A2XMs3KFPnRexeC9wvyiReDWBmBFFAd5fTfPOJBnz0BogIRsBkYtW3paipRT9xx5fL7AQ2FFvYkR7jRVFzTlkZbWMvjxJ9zrTjoOb44iMdUb1zBhEeHDg/su0ihwrpjgeN1J16/HFZCmzpEQphh/d22WtnB5L9f6YE9fl1FE6po= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e9Ys+0kp; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="e9Ys+0kp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91B64C2BCB8; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153354; bh=pxqba9wmZxQ1nmSRgyrt1Z9u0BBfiTIH8Z8HAWwBMIY=; h=Date:From:To:Cc:Subject:References:From; b=e9Ys+0kpPkBegDc91VSk9tM9lKBL2yRWbNPkEqGuKwYuHAgL4AwA5b6w9Dmyh8az+ 3qiUwsMsmK3sSZRsU+/LLC6RJhtPrQCU7dUVCGz6HhAR7yoylrjA0itIeLZPJmBxBG nj6iFq6YCmpNGjugvHAIWa9Jm25V5Mcr5Rtj2a2XuQ2slA5oNAmRcutUTN5DuMxnwi 2dIBRB9ClBZrehPYPa3rM62lA1p3g3r6O6uooIAJJa4fILnafkxOMz1nY4y+MyIvVy YwVn0uPWaUV37DaOHnbpm6roPntzzEIStTUpTeF7Qf3e74GYg26k5Y6YewOoPGhAiY oy0kyEk/TFU6g== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBo-00000002Zfl-2ykJ; Tue, 10 Mar 2026 10:36:04 -0400 Message-ID: <20260310143604.573386927@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:28 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 13/18] tracing: Introduce simple_ring_buffer References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Add a simple implementation of the kernel ring-buffer. This intends to be used later by ring-buffer remotes such as the pKVM hypervisor, hence the need for a cut down version (write only) without any dependency. Link: https://patch.msgid.link/20260309162516.2623589-14-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/simple_ring_buffer.h | 57 ++++ kernel/trace/Kconfig | 3 + kernel/trace/Makefile | 1 + kernel/trace/simple_ring_buffer.c | 464 +++++++++++++++++++++++++++++ 4 files changed, 525 insertions(+) create mode 100644 include/linux/simple_ring_buffer.h create mode 100644 kernel/trace/simple_ring_buffer.c diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring= _buffer.h new file mode 100644 index 000000000000..2c4c0ae336bc --- /dev/null +++ b/include/linux/simple_ring_buffer.h @@ -0,0 +1,57 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_SIMPLE_RING_BUFFER_H +#define _LINUX_SIMPLE_RING_BUFFER_H + +#include +#include +#include +#include + +/* + * Ideally those struct would stay private but the caller needs to know + * the allocation size for simple_ring_buffer_init(). + */ +struct simple_buffer_page { + struct list_head link; + struct buffer_data_page *page; + u64 entries; + u32 write; + u32 id; +}; + +struct simple_rb_per_cpu { + struct simple_buffer_page *tail_page; + struct simple_buffer_page *reader_page; + struct simple_buffer_page *head_page; + struct simple_buffer_page *bpages; + struct trace_buffer_meta *meta; + u32 nr_pages; + +#define SIMPLE_RB_UNAVAILABLE 0 +#define SIMPLE_RB_READY 1 +#define SIMPLE_RB_WRITING 2 + u32 status; + + u64 last_overrun; + u64 write_stamp; + + struct simple_rb_cbs *cbs; +}; + +int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct s= imple_buffer_page *bpages, + const struct ring_buffer_desc *desc); + +void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer); + +void *simple_ring_buffer_reserve(struct simple_rb_per_cpu *cpu_buffer, uns= igned long length, + u64 timestamp); + +void simple_ring_buffer_commit(struct simple_rb_per_cpu *cpu_buffer); + +int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer= , bool enable); + +int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer); + +int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buff= er); + +#endif diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 384dd36c8e29..edbdd7b38f61 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -1284,4 +1284,7 @@ source "kernel/trace/rv/Kconfig" config TRACE_REMOTE bool =20 +config SIMPLE_RING_BUFFER + bool + endif # FTRACE diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 318923ce39f5..2e39b09398b3 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -129,4 +129,5 @@ obj-$(CONFIG_TRACEPOINT_BENCHMARK) +=3D trace_benchmark= .o obj-$(CONFIG_RV) +=3D rv/ =20 obj-$(CONFIG_TRACE_REMOTE) +=3D trace_remote.o +obj-$(CONFIG_SIMPLE_RING_BUFFER) +=3D simple_ring_buffer.o libftrace-y :=3D ftrace.o diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_b= uffer.c new file mode 100644 index 000000000000..15df9781411b --- /dev/null +++ b/kernel/trace/simple_ring_buffer.c @@ -0,0 +1,464 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2025 - Google LLC + * Author: Vincent Donnefort + */ + +#include +#include + +#include +#include + +enum simple_rb_link_type { + SIMPLE_RB_LINK_NORMAL =3D 0, + SIMPLE_RB_LINK_HEAD =3D 1, + SIMPLE_RB_LINK_HEAD_MOVING +}; + +#define SIMPLE_RB_LINK_MASK ~(SIMPLE_RB_LINK_HEAD | SIMPLE_RB_LINK_HEAD_MO= VING) + +static void simple_bpage_set_head_link(struct simple_buffer_page *bpage) +{ + unsigned long link =3D (unsigned long)bpage->link.next; + + link &=3D SIMPLE_RB_LINK_MASK; + link |=3D SIMPLE_RB_LINK_HEAD; + + /* + * Paired with simple_rb_find_head() to order access between the head + * link and overrun. It ensures we always report an up-to-date value + * after swapping the reader page. + */ + smp_store_release(&bpage->link.next, (struct list_head *)link); +} + +static bool simple_bpage_unset_head_link(struct simple_buffer_page *bpage, + struct simple_buffer_page *dst, + enum simple_rb_link_type new_type) +{ + unsigned long *link =3D (unsigned long *)(&bpage->link.next); + unsigned long old =3D (*link & SIMPLE_RB_LINK_MASK) | SIMPLE_RB_LINK_HEAD; + unsigned long new =3D (unsigned long)(&dst->link) | new_type; + + return try_cmpxchg(link, &old, new); +} + +static void simple_bpage_set_normal_link(struct simple_buffer_page *bpage) +{ + unsigned long link =3D (unsigned long)bpage->link.next; + + WRITE_ONCE(bpage->link.next, (struct list_head *)(link & SIMPLE_RB_LINK_M= ASK)); +} + +static struct simple_buffer_page *simple_bpage_from_link(struct list_head = *link) +{ + unsigned long ptr =3D (unsigned long)link & SIMPLE_RB_LINK_MASK; + + return container_of((struct list_head *)ptr, struct simple_buffer_page, l= ink); +} + +static struct simple_buffer_page *simple_bpage_next_page(struct simple_buf= fer_page *bpage) +{ + return simple_bpage_from_link(bpage->link.next); +} + +static void simple_bpage_reset(struct simple_buffer_page *bpage) +{ + bpage->write =3D 0; + bpage->entries =3D 0; + + local_set(&bpage->page->commit, 0); +} + +static void simple_bpage_init(struct simple_buffer_page *bpage, unsigned l= ong page) +{ + INIT_LIST_HEAD(&bpage->link); + bpage->page =3D (struct buffer_data_page *)page; + + simple_bpage_reset(bpage); +} + +#define simple_rb_meta_inc(__meta, __inc) \ + WRITE_ONCE((__meta), (__meta + __inc)) + +static bool simple_rb_loaded(struct simple_rb_per_cpu *cpu_buffer) +{ + return !!cpu_buffer->bpages; +} + +static int simple_rb_find_head(struct simple_rb_per_cpu *cpu_buffer) +{ + int retry =3D cpu_buffer->nr_pages * 2; + struct simple_buffer_page *head; + + head =3D cpu_buffer->head_page; + + while (retry--) { + unsigned long link; + +spin: + /* See smp_store_release in simple_bpage_set_head_link() */ + link =3D (unsigned long)smp_load_acquire(&head->link.prev->next); + + switch (link & ~SIMPLE_RB_LINK_MASK) { + /* Found the head */ + case SIMPLE_RB_LINK_HEAD: + cpu_buffer->head_page =3D head; + return 0; + /* The writer caught the head, we can spin, that won't be long */ + case SIMPLE_RB_LINK_HEAD_MOVING: + goto spin; + } + + head =3D simple_bpage_next_page(head); + } + + return -EBUSY; +} + +/** + * simple_ring_buffer_swap_reader_page - Swap ring-buffer head with the re= ader + * @cpu_buffer: A simple_rb_per_cpu + * + * This function enables consuming reading. It ensures the current head pa= ge will not be overwritten + * and can be safely read. + * + * Returns 0 on success, -ENODEV if @cpu_buffer was unloaded or -EBUSY if = we failed to catch the + * head page. + */ +int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buff= er) +{ + struct simple_buffer_page *last, *head, *reader; + unsigned long overrun; + int retry =3D 8; + int ret; + + if (!simple_rb_loaded(cpu_buffer)) + return -ENODEV; + + reader =3D cpu_buffer->reader_page; + + do { + /* Run after the writer to find the head */ + ret =3D simple_rb_find_head(cpu_buffer); + if (ret) + return ret; + + head =3D cpu_buffer->head_page; + + /* Connect the reader page around the header page */ + reader->link.next =3D head->link.next; + reader->link.prev =3D head->link.prev; + + /* The last page before the head */ + last =3D simple_bpage_from_link(head->link.prev); + + /* The reader page points to the new header page */ + simple_bpage_set_head_link(reader); + + overrun =3D cpu_buffer->meta->overrun; + } while (!simple_bpage_unset_head_link(last, reader, SIMPLE_RB_LINK_NORMA= L) && retry--); + + if (!retry) + return -EINVAL; + + cpu_buffer->head_page =3D simple_bpage_from_link(reader->link.next); + cpu_buffer->head_page->link.prev =3D &reader->link; + cpu_buffer->reader_page =3D head; + cpu_buffer->meta->reader.lost_events =3D overrun - cpu_buffer->last_overr= un; + cpu_buffer->meta->reader.id =3D cpu_buffer->reader_page->id; + cpu_buffer->last_overrun =3D overrun; + + return 0; +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_swap_reader_page); + +static struct simple_buffer_page *simple_rb_move_tail(struct simple_rb_per= _cpu *cpu_buffer) +{ + struct simple_buffer_page *tail, *new_tail; + + tail =3D cpu_buffer->tail_page; + new_tail =3D simple_bpage_next_page(tail); + + if (simple_bpage_unset_head_link(tail, new_tail, SIMPLE_RB_LINK_HEAD_MOVI= NG)) { + /* + * Oh no! we've caught the head. There is none anymore and + * swap_reader will spin until we set the new one. Overrun must + * be written first, to make sure we report the correct number + * of lost events. + */ + simple_rb_meta_inc(cpu_buffer->meta->overrun, new_tail->entries); + simple_rb_meta_inc(cpu_buffer->meta->pages_lost, 1); + + simple_bpage_set_head_link(new_tail); + simple_bpage_set_normal_link(tail); + } + + simple_bpage_reset(new_tail); + cpu_buffer->tail_page =3D new_tail; + + simple_rb_meta_inc(cpu_buffer->meta->pages_touched, 1); + + return new_tail; +} + +static unsigned long rb_event_size(unsigned long length) +{ + struct ring_buffer_event *event; + + return length + RB_EVNT_HDR_SIZE + sizeof(event->array[0]); +} + +static struct ring_buffer_event * +rb_event_add_ts_extend(struct ring_buffer_event *event, u64 delta) +{ + event->type_len =3D RINGBUF_TYPE_TIME_EXTEND; + event->time_delta =3D delta & TS_MASK; + event->array[0] =3D delta >> TS_SHIFT; + + return (struct ring_buffer_event *)((unsigned long)event + 8); +} + +static struct ring_buffer_event * +simple_rb_reserve_next(struct simple_rb_per_cpu *cpu_buffer, unsigned long= length, u64 timestamp) +{ + unsigned long ts_ext_size =3D 0, event_size =3D rb_event_size(length); + struct simple_buffer_page *tail =3D cpu_buffer->tail_page; + struct ring_buffer_event *event; + u32 write, prev_write; + u64 time_delta; + + time_delta =3D timestamp - cpu_buffer->write_stamp; + + if (test_time_stamp(time_delta)) + ts_ext_size =3D 8; + + prev_write =3D tail->write; + write =3D prev_write + event_size + ts_ext_size; + + if (unlikely(write > (PAGE_SIZE - BUF_PAGE_HDR_SIZE))) + tail =3D simple_rb_move_tail(cpu_buffer); + + if (!tail->entries) { + tail->page->time_stamp =3D timestamp; + time_delta =3D 0; + ts_ext_size =3D 0; + write =3D event_size; + prev_write =3D 0; + } + + tail->write =3D write; + tail->entries++; + + cpu_buffer->write_stamp =3D timestamp; + + event =3D (struct ring_buffer_event *)(tail->page->data + prev_write); + if (ts_ext_size) { + event =3D rb_event_add_ts_extend(event, time_delta); + time_delta =3D 0; + } + + event->type_len =3D 0; + event->time_delta =3D time_delta; + event->array[0] =3D event_size - RB_EVNT_HDR_SIZE; + + return event; +} + +/** + * simple_ring_buffer_reserve - Reserve an entry in @cpu_buffer + * @cpu_buffer: A simple_rb_per_cpu + * @length: Size of the entry in bytes + * @timestamp: Timestamp of the entry + * + * Returns the address of the entry where to write data or NULL + */ +void *simple_ring_buffer_reserve(struct simple_rb_per_cpu *cpu_buffer, uns= igned long length, + u64 timestamp) +{ + struct ring_buffer_event *rb_event; + + if (cmpxchg(&cpu_buffer->status, SIMPLE_RB_READY, SIMPLE_RB_WRITING) !=3D= SIMPLE_RB_READY) + return NULL; + + rb_event =3D simple_rb_reserve_next(cpu_buffer, length, timestamp); + + return &rb_event->array[1]; +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_reserve); + +/** + * simple_ring_buffer_commit - Commit the entry reserved with simple_ring_= buffer_reserve() + * @cpu_buffer: The simple_rb_per_cpu where the entry has been reserved + */ +void simple_ring_buffer_commit(struct simple_rb_per_cpu *cpu_buffer) +{ + local_set(&cpu_buffer->tail_page->page->commit, + cpu_buffer->tail_page->write); + simple_rb_meta_inc(cpu_buffer->meta->entries, 1); + + /* + * Paired with simple_rb_enable_tracing() to ensure data is + * written to the ring-buffer before teardown. + */ + smp_store_release(&cpu_buffer->status, SIMPLE_RB_READY); +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_commit); + +static u32 simple_rb_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, = bool enable) +{ + u32 prev_status; + + if (enable) + return cmpxchg(&cpu_buffer->status, SIMPLE_RB_UNAVAILABLE, SIMPLE_RB_REA= DY); + + /* Wait for the buffer to be released */ + do { + prev_status =3D cmpxchg_acquire(&cpu_buffer->status, + SIMPLE_RB_READY, + SIMPLE_RB_UNAVAILABLE); + } while (prev_status =3D=3D SIMPLE_RB_WRITING); + + return prev_status; +} + +/** + * simple_ring_buffer_reset - Reset @cpu_buffer + * @cpu_buffer: A simple_rb_per_cpu + * + * This will not clear the content of the data, only reset counters and po= inters + * + * Returns 0 on success or -ENODEV if @cpu_buffer was unloaded. + */ +int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer) +{ + struct simple_buffer_page *bpage; + u32 prev_status; + int ret; + + if (!simple_rb_loaded(cpu_buffer)) + return -ENODEV; + + prev_status =3D simple_rb_enable_tracing(cpu_buffer, false); + + ret =3D simple_rb_find_head(cpu_buffer); + if (ret) + return ret; + + bpage =3D cpu_buffer->tail_page =3D cpu_buffer->head_page; + do { + simple_bpage_reset(bpage); + bpage =3D simple_bpage_next_page(bpage); + } while (bpage !=3D cpu_buffer->head_page); + + simple_bpage_reset(cpu_buffer->reader_page); + + cpu_buffer->last_overrun =3D 0; + cpu_buffer->write_stamp =3D 0; + + cpu_buffer->meta->reader.read =3D 0; + cpu_buffer->meta->reader.lost_events =3D 0; + cpu_buffer->meta->entries =3D 0; + cpu_buffer->meta->overrun =3D 0; + cpu_buffer->meta->read =3D 0; + cpu_buffer->meta->pages_lost =3D 0; + cpu_buffer->meta->pages_touched =3D 0; + + if (prev_status =3D=3D SIMPLE_RB_READY) + simple_rb_enable_tracing(cpu_buffer, true); + + return 0; +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_reset); + +/** + * simple_ring_buffer_init - Init @cpu_buffer based on @desc + * @cpu_buffer: A simple_rb_per_cpu buffer to init, allocated by the calle= r. + * @bpages: Array of simple_buffer_pages, with as many elements as @desc->= nr_page_va + * @desc: A ring_buffer_desc + * + * Returns 0 on success or -EINVAL if the content of @desc is invalid + */ +int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct s= imple_buffer_page *bpages, + const struct ring_buffer_desc *desc) +{ + struct simple_buffer_page *bpage =3D bpages; + int i; + + /* At least 1 reader page and two pages in the ring-buffer */ + if (desc->nr_page_va < 3) + return -EINVAL; + + memset(cpu_buffer, 0, sizeof(*cpu_buffer)); + + cpu_buffer->bpages =3D bpages; + + cpu_buffer->meta =3D (void *)desc->meta_va; + memset(cpu_buffer->meta, 0, sizeof(*cpu_buffer->meta)); + cpu_buffer->meta->meta_page_size =3D PAGE_SIZE; + cpu_buffer->meta->nr_subbufs =3D cpu_buffer->nr_pages; + + /* The reader page is not part of the ring initially */ + simple_bpage_init(bpage, desc->page_va[0]); + bpage->id =3D 0; + + cpu_buffer->nr_pages =3D 1; + + cpu_buffer->reader_page =3D bpage; + cpu_buffer->tail_page =3D bpage + 1; + cpu_buffer->head_page =3D bpage + 1; + + for (i =3D 1; i < desc->nr_page_va; i++) { + simple_bpage_init(++bpage, desc->page_va[i]); + + bpage->link.next =3D &(bpage + 1)->link; + bpage->link.prev =3D &(bpage - 1)->link; + bpage->id =3D i; + + cpu_buffer->nr_pages =3D i + 1; + } + + /* Close the ring */ + bpage->link.next =3D &cpu_buffer->tail_page->link; + cpu_buffer->tail_page->link.prev =3D &bpage->link; + + /* The last init'ed page points to the head page */ + simple_bpage_set_head_link(bpage); + + return 0; +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_init); + +/** + * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion + * @cpu_buffer: A simple_rb_per_cpu that will be deleted. + */ +void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer) +{ + if (!simple_rb_loaded(cpu_buffer)) + return; + + simple_rb_enable_tracing(cpu_buffer, false); + + cpu_buffer->bpages =3D NULL; +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_unload); + +/** + * simple_ring_buffer_enable_tracing - Enable or disable writing to @cpu_b= uffer + * @cpu_buffer: A simple_rb_per_cpu + * @enable: True to enable tracing, False to disable it + * + * Returns 0 on success or -ENODEV if @cpu_buffer was unloaded + */ +int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer= , bool enable) +{ + if (!simple_rb_loaded(cpu_buffer)) + return -ENODEV; + + simple_rb_enable_tracing(cpu_buffer, enable); + + return 0; +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_enable_tracing); --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DDCD8303C86 for ; Tue, 10 Mar 2026 14:35:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; cv=none; b=QTbxvaW3fq+n+jCvYnYCtj+JNlr3CPoSUeD5N5O8DhFN4V7u2fbn0cl48OL1cz1JJ2I7XiPe9XdeIeeQrYbaslIrXv/aBcLaDrGGw1NU3pMENzhBdvLzm6kSkHD9J+i6IH3p9XGz8wzwbTmf+biXpdF1c8VJNKx6WJoUbNhM5fM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153354; c=relaxed/simple; bh=vj1YF0cl1fNkARio0i51WfJ2dTUZKrMg70YErMrOk0E=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; 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Tue, 10 Mar 2026 10:36:04 -0400 Message-ID: <20260310143604.727717981@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:29 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 14/18] tracing: Add a trace remote module for testing References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Add a module to help testing the tracefs support for trace remotes. This module: * Use simple_ring_buffer to write into a ring-buffer. * Declare a single "selftest" event that can be triggered from user-space. * Register a "test" trace remote. This is intended to be used by trace remote selftests. Link: https://patch.msgid.link/20260309162516.2623589-15-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- fs/tracefs/inode.c | 1 + kernel/trace/Kconfig | 8 + kernel/trace/Makefile | 2 + kernel/trace/remote_test.c | 261 ++++++++++++++++++++++++++++++ kernel/trace/remote_test_events.h | 10 ++ 5 files changed, 282 insertions(+) create mode 100644 kernel/trace/remote_test.c create mode 100644 kernel/trace/remote_test_events.h diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 51c00c8fa175..edfdf139cb02 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -664,6 +664,7 @@ struct dentry *tracefs_create_file(const char *name, um= ode_t mode, fsnotify_create(d_inode(dentry->d_parent), dentry); return tracefs_end_creating(dentry); } +EXPORT_SYMBOL_GPL(tracefs_create_file); =20 static struct dentry *__create_dir(const char *name, struct dentry *parent, const struct inode_operations *ops) diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index edbdd7b38f61..e130da35808f 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -1287,4 +1287,12 @@ config TRACE_REMOTE config SIMPLE_RING_BUFFER bool =20 +config TRACE_REMOTE_TEST + tristate "Test module for remote tracing" + select TRACE_REMOTE + select SIMPLE_RING_BUFFER + help + This trace remote includes a ring-buffer writer implementation using + "simple_ring_buffer". This is solely intending for testing. + endif # FTRACE diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 2e39b09398b3..d106beca8d7f 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -130,4 +130,6 @@ obj-$(CONFIG_RV) +=3D rv/ =20 obj-$(CONFIG_TRACE_REMOTE) +=3D trace_remote.o obj-$(CONFIG_SIMPLE_RING_BUFFER) +=3D simple_ring_buffer.o +obj-$(CONFIG_TRACE_REMOTE_TEST) +=3D remote_test.o + libftrace-y :=3D ftrace.o diff --git a/kernel/trace/remote_test.c b/kernel/trace/remote_test.c new file mode 100644 index 000000000000..6c1b7701ddae --- /dev/null +++ b/kernel/trace/remote_test.c @@ -0,0 +1,261 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2025 - Google LLC + * Author: Vincent Donnefort + */ + +#include +#include +#include +#include +#include + +#define REMOTE_EVENT_INCLUDE_FILE kernel/trace/remote_test_events.h +#include + +static DEFINE_PER_CPU(struct simple_rb_per_cpu *, simple_rbs); +static struct trace_buffer_desc *remote_test_buffer_desc; + +/* + * The trace_remote lock already serializes accesses from the trace_remote= _callbacks. + * However write_event can still race with load/unload. + */ +static DEFINE_MUTEX(simple_rbs_lock); + +static int remote_test_load_simple_rb(int cpu, struct ring_buffer_desc *rb= _desc) +{ + struct simple_rb_per_cpu *cpu_buffer; + struct simple_buffer_page *bpages; + int ret =3D -ENOMEM; + + cpu_buffer =3D kmalloc_obj(*cpu_buffer); + if (!cpu_buffer) + return ret; + + bpages =3D kmalloc_objs(*bpages, rb_desc->nr_page_va); + if (!bpages) + goto err_free_cpu_buffer; + + ret =3D simple_ring_buffer_init(cpu_buffer, bpages, rb_desc); + if (ret) + goto err_free_bpages; + + scoped_guard(mutex, &simple_rbs_lock) { + WARN_ON(*per_cpu_ptr(&simple_rbs, cpu)); + *per_cpu_ptr(&simple_rbs, cpu) =3D cpu_buffer; + } + + return 0; + +err_free_bpages: + kfree(bpages); + +err_free_cpu_buffer: + kfree(cpu_buffer); + + return ret; +} + +static void remote_test_unload_simple_rb(int cpu) +{ + struct simple_rb_per_cpu *cpu_buffer =3D *per_cpu_ptr(&simple_rbs, cpu); + struct simple_buffer_page *bpages; + + if (!cpu_buffer) + return; + + guard(mutex)(&simple_rbs_lock); + + bpages =3D cpu_buffer->bpages; + simple_ring_buffer_unload(cpu_buffer); + kfree(bpages); + kfree(cpu_buffer); + *per_cpu_ptr(&simple_rbs, cpu) =3D NULL; +} + +static struct trace_buffer_desc *remote_test_load(unsigned long size, void= *unused) +{ + struct ring_buffer_desc *rb_desc; + struct trace_buffer_desc *desc; + size_t desc_size; + int cpu, ret; + + if (WARN_ON(remote_test_buffer_desc)) + return ERR_PTR(-EINVAL); + + desc_size =3D trace_buffer_desc_size(size, num_possible_cpus()); + if (desc_size =3D=3D SIZE_MAX) { + ret =3D -E2BIG; + goto err; + } + + desc =3D kmalloc(desc_size, GFP_KERNEL); + if (!desc) { + ret =3D -ENOMEM; + goto err; + } + + ret =3D trace_remote_alloc_buffer(desc, desc_size, size, cpu_possible_mas= k); + if (ret) + goto err_free_desc; + + for_each_ring_buffer_desc(rb_desc, cpu, desc) { + ret =3D remote_test_load_simple_rb(rb_desc->cpu, rb_desc); + if (ret) + goto err_unload; + } + + remote_test_buffer_desc =3D desc; + + return remote_test_buffer_desc; + +err_unload: + for_each_ring_buffer_desc(rb_desc, cpu, remote_test_buffer_desc) + remote_test_unload_simple_rb(rb_desc->cpu); + trace_remote_free_buffer(remote_test_buffer_desc); + +err_free_desc: + kfree(desc); + +err: + return ERR_PTR(ret); +} + +static void remote_test_unload(struct trace_buffer_desc *desc, void *unuse= d) +{ + struct ring_buffer_desc *rb_desc; + int cpu; + + if (WARN_ON(desc !=3D remote_test_buffer_desc)) + return; + + for_each_ring_buffer_desc(rb_desc, cpu, desc) + remote_test_unload_simple_rb(rb_desc->cpu); + + remote_test_buffer_desc =3D NULL; + trace_remote_free_buffer(desc); + kfree(desc); +} + +static int remote_test_enable_tracing(bool enable, void *unused) +{ + struct ring_buffer_desc *rb_desc; + int cpu; + + if (!remote_test_buffer_desc) + return -ENODEV; + + for_each_ring_buffer_desc(rb_desc, cpu, remote_test_buffer_desc) + WARN_ON(simple_ring_buffer_enable_tracing(*per_cpu_ptr(&simple_rbs, rb_d= esc->cpu), + enable)); + return 0; +} + +static int remote_test_swap_reader_page(unsigned int cpu, void *unused) +{ + struct simple_rb_per_cpu *cpu_buffer; + + if (cpu >=3D NR_CPUS) + return -EINVAL; + + cpu_buffer =3D *per_cpu_ptr(&simple_rbs, cpu); + if (!cpu_buffer) + return -EINVAL; + + return simple_ring_buffer_swap_reader_page(cpu_buffer); +} + +static int remote_test_reset(unsigned int cpu, void *unused) +{ + struct simple_rb_per_cpu *cpu_buffer; + + if (cpu >=3D NR_CPUS) + return -EINVAL; + + cpu_buffer =3D *per_cpu_ptr(&simple_rbs, cpu); + if (!cpu_buffer) + return -EINVAL; + + return simple_ring_buffer_reset(cpu_buffer); +} + +static int remote_test_enable_event(unsigned short id, bool enable, void *= unused) +{ + if (id !=3D REMOTE_TEST_EVENT_ID) + return -EINVAL; + + /* + * Let's just use the struct remote_event enabled field that is turned on= and off by + * trace_remote. This is a bit racy but good enough for a simple test mod= ule. + */ + return 0; +} + +static ssize_t +write_event_write(struct file *filp, const char __user *ubuf, size_t cnt, = loff_t *pos) +{ + struct remote_event_format_selftest *evt_test; + struct simple_rb_per_cpu *cpu_buffer; + unsigned long val; + int ret; + + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); + if (ret) + return ret; + + guard(mutex)(&simple_rbs_lock); + + if (!remote_event_selftest.enabled) + return -ENODEV; + + guard(preempt)(); + + cpu_buffer =3D *this_cpu_ptr(&simple_rbs); + if (!cpu_buffer) + return -ENODEV; + + evt_test =3D simple_ring_buffer_reserve(cpu_buffer, + sizeof(struct remote_event_format_selftest), + trace_clock_global()); + if (!evt_test) + return -ENODEV; + + evt_test->hdr.id =3D REMOTE_TEST_EVENT_ID; + evt_test->id =3D val; + + simple_ring_buffer_commit(cpu_buffer); + + return cnt; +} + +static const struct file_operations write_event_fops =3D { + .write =3D write_event_write, +}; + +static int remote_test_init_tracefs(struct dentry *d, void *unused) +{ + return tracefs_create_file("write_event", 0200, d, NULL, &write_event_fop= s) ? + 0 : -ENOMEM; +} + +static struct trace_remote_callbacks trace_remote_callbacks =3D { + .init =3D remote_test_init_tracefs, + .load_trace_buffer =3D remote_test_load, + .unload_trace_buffer =3D remote_test_unload, + .enable_tracing =3D remote_test_enable_tracing, + .swap_reader_page =3D remote_test_swap_reader_page, + .reset =3D remote_test_reset, + .enable_event =3D remote_test_enable_event, +}; + +static int __init remote_test_init(void) +{ + return trace_remote_register("test", &trace_remote_callbacks, NULL, + &remote_event_selftest, 1); +} + +module_init(remote_test_init); + +MODULE_DESCRIPTION("Test module for the trace remote interface"); +MODULE_AUTHOR("Vincent Donnefort"); +MODULE_LICENSE("GPL"); diff --git a/kernel/trace/remote_test_events.h b/kernel/trace/remote_test_e= vents.h new file mode 100644 index 000000000000..26b93b3406fc --- /dev/null +++ b/kernel/trace/remote_test_events.h @@ -0,0 +1,10 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#define REMOTE_TEST_EVENT_ID 1 + +REMOTE_EVENT(selftest, REMOTE_TEST_EVENT_ID, + RE_STRUCT( + re_field(u64, id) + ), + RE_PRINTK("id=3D%llu", __entry->id) +); 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Tue, 10 Mar 2026 10:36:04 -0400 Message-ID: <20260310143604.871487687@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:30 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort , Shuah Khan , linux-kselftest@vger.kernel.org Subject: [for-next][PATCH 15/18] tracing: selftests: Add trace remote tests References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Exercise the tracefs interface for trace remote with a set of tests to check: * loading/unloading (unloading.tc) * reset (reset.tc) * size changes (buffer_size.tc) * consuming read (trace_pipe.tc) * non-consuming read (trace.tc) Cc: Shuah Khan Cc: linux-kselftest@vger.kernel.org Link: https://patch.msgid.link/20260309162516.2623589-16-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- .../ftrace/test.d/remotes/buffer_size.tc | 25 ++++ .../selftests/ftrace/test.d/remotes/functions | 88 ++++++++++++ .../selftests/ftrace/test.d/remotes/reset.tc | 90 +++++++++++++ .../selftests/ftrace/test.d/remotes/trace.tc | 127 ++++++++++++++++++ .../ftrace/test.d/remotes/trace_pipe.tc | 127 ++++++++++++++++++ .../ftrace/test.d/remotes/unloading.tc | 41 ++++++ 6 files changed, 498 insertions(+) create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/buffer_si= ze.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/functions create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/reset.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/trace.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/trace_pip= e.tc create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/unloading= .tc diff --git a/tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc b= /tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc new file mode 100644 index 000000000000..1a43280ffa97 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc @@ -0,0 +1,25 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test trace remote buffer size +# requires: remotes/test + +. $TEST_DIR/remotes/functions + +test_buffer_size() +{ + echo 0 > tracing_on + assert_unloaded + + echo 4096 > buffer_size_kb + echo 1 > tracing_on + assert_loaded + + echo 0 > tracing_on + echo 7 > buffer_size_kb +} + +if [ -z "$SOURCE_REMOTE_TEST" ]; then + set -e + setup_remote_test + test_buffer_size +fi diff --git a/tools/testing/selftests/ftrace/test.d/remotes/functions b/tool= s/testing/selftests/ftrace/test.d/remotes/functions new file mode 100644 index 000000000000..97a09d564a34 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/remotes/functions @@ -0,0 +1,88 @@ +# SPDX-License-Identifier: GPL-2.0 + +setup_remote() +{ + local name=3D$1 + + [ -e $TRACING_DIR/remotes/$name/write_event ] || exit_unresolved + + cd remotes/$name/ + echo 0 > tracing_on + clear_trace + echo 7 > buffer_size_kb + echo 0 > events/enable + echo 1 > events/$name/selftest/enable + echo 1 > tracing_on +} + +setup_remote_test() +{ + [ -d $TRACING_DIR/remotes/test/ ] || modprobe remote_test || exit_unresol= ved + + setup_remote "test" +} + +assert_loaded() +{ + grep -q "(loaded)" buffer_size_kb +} + +assert_unloaded() +{ + grep -q "(unloaded)" buffer_size_kb +} + +dump_trace_pipe() +{ + output=3D$(mktemp $TMPDIR/remote_test.XXXXXX) + cat trace_pipe > $output & + pid=3D$! + sleep 1 + kill -1 $pid + + echo $output +} + +check_trace() +{ + start_id=3D"$1" + end_id=3D"$2" + file=3D"$3" + + # Ensure the file is not empty + test -n "$(head $file)" + + prev_ts=3D0 + id=3D0 + + # Only keep + tmp=3D$(mktemp $TMPDIR/remote_test.XXXXXX) + sed -e 's/\[[0-9]*\]\s*\([0-9]*.[0-9]*\): [a-z]* id=3D\([0-9]*\)/\1 \2/' = $file > $tmp + + while IFS=3D read -r line; do + ts=3D$(echo $line | cut -d ' ' -f 1) + id=3D$(echo $line | cut -d ' ' -f 2) + + test $(echo "$ts>$prev_ts" | bc) -eq 1 + test $id -eq $start_id + + prev_ts=3D$ts + start_id=3D$((start_id + 1)) + done < $tmp + + test $id -eq $end_id + rm $tmp +} + +get_cpu_ids() +{ + sed -n 's/^processor\s*:\s*\([0-9]\+\).*/\1/p' /proc/cpuinfo +} + +get_page_size() { + sed -ne 's/^.*data.*size:\([0-9][0-9]*\).*/\1/p' events/header_page +} + +get_selftest_event_size() { + sed -ne 's/^.*field:.*;.*size:\([0-9][0-9]*\);.*/\1/p' events/*/selfte= st/format | awk '{s+=3D$1} END {print s}' +} diff --git a/tools/testing/selftests/ftrace/test.d/remotes/reset.tc b/tools= /testing/selftests/ftrace/test.d/remotes/reset.tc new file mode 100644 index 000000000000..4d176349b2bc --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/remotes/reset.tc @@ -0,0 +1,90 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test trace remote reset +# requires: remotes/test + +. $TEST_DIR/remotes/functions + +check_reset() +{ + write_event_path=3D"write_event" + taskset=3D"" + + clear_trace + + # Is the buffer empty? + output=3D$(dump_trace_pipe) + test $(wc -l $output | cut -d ' ' -f1) -eq 0 + + if $(echo $(pwd) | grep -q "per_cpu/cpu"); then + write_event_path=3D"../../write_event" + cpu_id=3D$(echo $(pwd) | sed -e 's/.*per_cpu\/cpu//') + taskset=3D"taskset -c $cpu_id" + fi + rm $output + + # Can we properly write a new event? + $taskset echo 7890 > $write_event_path + output=3D$(dump_trace_pipe) + test $(wc -l $output | cut -d ' ' -f1) -eq 1 + grep -q "id=3D7890" $output + rm $output +} + +test_global_interface() +{ + output=3D$(mktemp $TMPDIR/remote_test.XXXXXX) + + # Confidence check + echo 123456 > write_event + output=3D$(dump_trace_pipe) + grep -q "id=3D123456" $output + rm $output + + # Reset single event + echo 1 > write_event + check_reset + + # Reset lost events + for i in $(seq 1 10000); do + echo 1 > write_event + done + check_reset +} + +test_percpu_interface() +{ + [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0 + + for cpu in $(get_cpu_ids); do + taskset -c $cpu echo 1 > write_event + done + + check_non_empty=3D0 + for cpu in $(get_cpu_ids); do + cd per_cpu/cpu$cpu/ + + if [ $check_non_empty -eq 0 ]; then + check_reset + check_non_empty=3D1 + else + # Check we have only reset 1 CPU + output=3D$(dump_trace_pipe) + test $(wc -l $output | cut -d ' ' -f1) -eq 1 + rm $output + fi + cd - + done +} + +test_reset() +{ + test_global_interface + test_percpu_interface +} + +if [ -z "$SOURCE_REMOTE_TEST" ]; then + set -e + setup_remote_test + test_reset +fi diff --git a/tools/testing/selftests/ftrace/test.d/remotes/trace.tc b/tools= /testing/selftests/ftrace/test.d/remotes/trace.tc new file mode 100644 index 000000000000..170f7648732a --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/remotes/trace.tc @@ -0,0 +1,127 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test trace remote non-consuming read +# requires: remotes/test + +. $TEST_DIR/remotes/functions + +test_trace() +{ + echo 0 > tracing_on + assert_unloaded + + echo 7 > buffer_size_kb + echo 1 > tracing_on + assert_loaded + + # Simple test: Emit few events and try to read them + for i in $(seq 1 8); do + echo $i > write_event + done + + check_trace 1 8 trace + + # + # Test interaction with consuming read + # + + cat trace_pipe > /dev/null & + pid=3D$! + + sleep 1 + kill $pid + + test $(wc -l < trace) -eq 0 + + for i in $(seq 16 32); do + echo $i > write_event + done + + check_trace 16 32 trace + + # + # Test interaction with reset + # + + echo 0 > trace + + test $(wc -l < trace) -eq 0 + + for i in $(seq 1 8); do + echo $i > write_event + done + + check_trace 1 8 trace + + # + # Test interaction with lost events + # + + # Ensure the writer is not on the reader page by reloading the buffer + echo 0 > tracing_on + echo 0 > trace + assert_unloaded + echo 1 > tracing_on + assert_loaded + + # Ensure ring-buffer overflow by emitting events from the same CPU + for cpu in $(get_cpu_ids); do + break + done + + events_per_page=3D$(($(get_page_size) / $(get_selftest_event_size))) #= Approx: does not take TS into account + nr_events=3D$(($events_per_page * 2)) + for i in $(seq 1 $nr_events); do + taskset -c $cpu echo $i > write_event + done + + id=3D$(sed -n -e '1s/\[[0-9]*\]\s*[0-9]*.[0-9]*: [a-z]* id=3D\([0-9]*\= )/\1/p' trace) + test $id -ne 1 + + check_trace $id $nr_events trace + + # + # Test per-CPU interface + # + echo 0 > trace + + for cpu in $(get_cpu_ids) ; do + taskset -c $cpu echo $cpu > write_event + done + + for cpu in $(get_cpu_ids); do + cd per_cpu/cpu$cpu/ + + check_trace $cpu $cpu trace + + cd - > /dev/null + done + + # + # Test with hotplug + # + + [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0 + + echo 0 > trace + + for cpu in $(get_cpu_ids); do + echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 0 + break + done + + for i in $(seq 1 8); do + echo $i > write_event + done + + check_trace 1 8 trace + + echo 1 > /sys/devices/system/cpu/cpu$cpu/online +} + +if [ -z "$SOURCE_REMOTE_TEST" ]; then + set -e + + setup_remote_test + test_trace +fi diff --git a/tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc b/= tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc new file mode 100644 index 000000000000..669a7288ed7c --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc @@ -0,0 +1,127 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test trace remote consuming read +# requires: remotes/test + +. $TEST_DIR/remotes/functions + +test_trace_pipe() +{ + echo 0 > tracing_on + assert_unloaded + + # Emit events from the same CPU + for cpu in $(get_cpu_ids); do + break + done + + # + # Simple test: Emit enough events to fill few pages + # + + echo 1024 > buffer_size_kb + echo 1 > tracing_on + assert_loaded + + events_per_page=3D$(($(get_page_size) / $(get_selftest_event_size))) + nr_events=3D$(($events_per_page * 4)) + + output=3D$(mktemp $TMPDIR/remote_test.XXXXXX) + + cat trace_pipe > $output & + pid=3D$! + + for i in $(seq 1 $nr_events); do + taskset -c $cpu echo $i > write_event + done + + echo 0 > tracing_on + sleep 1 + kill $pid + + check_trace 1 $nr_events $output + + rm $output + + # + # Test interaction with lost events + # + + assert_unloaded + echo 7 > buffer_size_kb + echo 1 > tracing_on + assert_loaded + + nr_events=3D$((events_per_page * 2)) + for i in $(seq 1 $nr_events); do + taskset -c $cpu echo $i > write_event + done + + output=3D$(dump_trace_pipe) + + lost_events=3D$(sed -n -e '1s/CPU:.*\[LOST \([0-9]*\) EVENTS\]/\1/p' $= output) + test -n "$lost_events" + + id=3D$(sed -n -e '2s/\[[0-9]*\]\s*[0-9]*.[0-9]*: [a-z]* id=3D\([0-9]*\= )/\1/p' $output) + test "$id" -eq $(($lost_events + 1)) + + # Drop [LOST EVENTS] line + sed -i '1d' $output + + check_trace $id $nr_events $output + + rm $output + + # + # Test per-CPU interface + # + + echo 0 > trace + echo 1 > tracing_on + + for cpu in $(get_cpu_ids); do + taskset -c $cpu echo $cpu > write_event + done + + for cpu in $(get_cpu_ids); do + cd per_cpu/cpu$cpu/ + output=3D$(dump_trace_pipe) + + check_trace $cpu $cpu $output + + rm $output + cd - > /dev/null + done + + # + # Test interaction with hotplug + # + + [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0 + + echo 0 > trace + + for cpu in $(get_cpu_ids); do + echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 0 + break + done + + for i in $(seq 1 8); do + echo $i > write_event + done + + output=3D$(dump_trace_pipe) + + check_trace 1 8 $output + + rm $output + + echo 1 > /sys/devices/system/cpu/cpu$cpu/online +} + +if [ -z "$SOURCE_REMOTE_TEST" ]; then + set -e + + setup_remote_test + test_trace_pipe +fi diff --git a/tools/testing/selftests/ftrace/test.d/remotes/unloading.tc b/t= ools/testing/selftests/ftrace/test.d/remotes/unloading.tc new file mode 100644 index 000000000000..cac2190183f6 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/remotes/unloading.tc @@ -0,0 +1,41 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test trace remote unloading +# requires: remotes/test + +. $TEST_DIR/remotes/functions + +test_unloading() +{ + # No reader, writing + assert_loaded + + # No reader, no writing + echo 0 > tracing_on + assert_unloaded + + # 1 reader, no writing + cat trace_pipe & + pid=3D$! + sleep 1 + assert_loaded + kill $pid + assert_unloaded + + # No reader, no writing, events + echo 1 > tracing_on + echo 1 > write_event + echo 0 > tracing_on + assert_loaded + + # Test reset + clear_trace + assert_unloaded +} + +if [ -z "$SOURCE_REMOTE_TEST" ]; 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Tue, 10 Mar 2026 10:36:05 -0400 Message-ID: <20260310143605.009065973@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:31 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 16/18] Documentation: tracing: Add tracing remotes References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Add documentation about the newly introduced tracing remotes framework. Link: https://patch.msgid.link/20260309162516.2623589-17-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- Documentation/trace/index.rst | 11 ++++++ Documentation/trace/remotes.rst | 66 +++++++++++++++++++++++++++++++++ 2 files changed, 77 insertions(+) create mode 100644 Documentation/trace/remotes.rst diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst index 338bc4d7cfab..036db96864d2 100644 --- a/Documentation/trace/index.rst +++ b/Documentation/trace/index.rst @@ -91,6 +91,17 @@ interactions. user_events uprobetracer =20 +Remote Tracing +-------------- + +This section covers the framework to read compatible ring-buffers, written= by +entities outside of the kernel (most likely firmware or hypervisor) + +.. toctree:: + :maxdepth: 1 + + remotes + Additional Resources -------------------- =20 diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.= rst new file mode 100644 index 000000000000..1f9d764f69aa --- /dev/null +++ b/Documentation/trace/remotes.rst @@ -0,0 +1,66 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Tracing Remotes +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +:Author: Vincent Donnefort + +Overview +=3D=3D=3D=3D=3D=3D=3D=3D +Firmware and hypervisors are black boxes to the kernel. Having a way to se= e what +they are doing can be useful to debug both. This is where remote tracing b= uffers +come in. A remote tracing buffer is a ring buffer executed by the firmware= or +hypervisor into memory that is memory mapped to the host kernel. This is s= imilar +to how user space memory maps the kernel ring buffer but in this case the = kernel +is acting like user space and the firmware or hypervisor is the "kernel" s= ide. +With a trace remote ring buffer, the firmware and hypervisor can record ev= ents +for which the host kernel can see and expose to user space. + +Register a remote +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +A remote must provide a set of callbacks `struct trace_remote_callbacks` w= hom +description can be found below. Those callbacks allows Tracefs to enable a= nd +disable tracing and events, to load and unload a tracing buffer (a set of +ring-buffers) and to swap a reader page with the head page, which enables +consuming reading. + +.. kernel-doc:: include/linux/trace_remote.h + +Once registered, an instance will appear for this remote in the Tracefs +directory **remotes/**. Buffers can then be read using the usual Tracefs f= iles +**trace_pipe** and **trace**. + +Declare a remote event +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Macros are provided to ease the declaration of remote events, in a similar +fashion to in-kernel events. A declaration must provide an ID, a descripti= on of +the event arguments and how to print the event: + +.. code-block:: c + + REMOTE_EVENT(foo, EVENT_FOO_ID, + RE_STRUCT( + re_field(u64, bar) + ), + RE_PRINTK("bar=3D%lld", __entry->bar) + ); + +Then those events must be declared in a C file with the following: + +.. code-block:: c + + #define REMOTE_EVENT_INCLUDE_FILE foo_events.h + #include + +This will provide a `struct remote_event remote_event_foo` that can be giv= en to +`trace_remote_register`. + +Registered events appear in the remote directory under **events/**. + +Simple ring-buffer +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +A simple implementation for a ring-buffer writer can be found in +kernel/trace/simple_ring_buffer.c. + +.. kernel-doc:: include/linux/simple_ring_buffer.h --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 42DC43064BA for ; Tue, 10 Mar 2026 14:35:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153355; cv=none; b=EV2F8xc9wkXiDRj0LhY3hqsYEIYb3heDRJIVvtZTf1qhVEJjVrE1hQr2XYeCVDLTv4hmz8GOp2j3qC9BEOpwJfNMXepbCwqIixZSDodlkSgUrCMWiBSjwoMGSHPRUn6JDCAIkWdsVdl0Y5/jnvdc4giRfVayh+IwrcFByS3wtnc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773153355; c=relaxed/simple; bh=yZaRDJzhNHXSgwxNUnGHn/vk/Ja0baRkFgfWvqMkbV4=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=HqZqAla5VEvxMbUEHlh6xzc2Dom3AdKZKGQ4fB6u0nHqHmLdw6lIpOo6Oqtog+Sb/p+8123b93W5ejZniO9isAt3buK9u50CI0K6hnd3rlyletZu003GYzRHV5NsPR/LvWItGyT/1dAymHqDuTp7DBvU+cSKvoAfdChRGzyDf94= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KdRnafut; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KdRnafut" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 24CFDC2BCB5; Tue, 10 Mar 2026 14:35:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773153355; bh=yZaRDJzhNHXSgwxNUnGHn/vk/Ja0baRkFgfWvqMkbV4=; h=Date:From:To:Cc:Subject:References:From; b=KdRnafutXipJi1CraNiT4hQU/2g5zuK+DtaovP/0s5TkLl7D8EEXIKqFDvONqLvUy YOlQTHGTpsVXAYPiNR1HL3rjip3VmcXeSQhC2KbFnVabqWanHWDDxvvZ4LowCnK5gX hNiab1Ptq0lBBB21Zr0EJ8OM8MBoOFZLjBOxaE9IuPfqo88Z9YeRNxXi5U0A6wXgAj y4PzLVTzyuMibxF3evroq9M9Qm5lfK652ML+UYr44Ja33EyoQFWSmwUIPYymV2bxJR y98I42/PvYSO9QKsvdUrwU/9xHQcqb/TP7HFJAlSEeNTDe5s98PkPf8+ylkYqmXhWs Vd+vQzuUdZMPA== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vzyBp-00000002Zhm-19sk; Tue, 10 Mar 2026 10:36:05 -0400 Message-ID: <20260310143605.149321389@kernel.org> User-Agent: quilt/0.69 Date: Tue, 10 Mar 2026 10:35:32 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 17/18] tracing: load/unload page callbacks for simple_ring_buffer References: <20260310143515.132579088@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Vincent Donnefort Add load/unload callback used for each admitted page in the ring-buffer. This will be later useful for the pKVM hypervisor which uses a different VA space and need to dynamically map/unmap the ring-buffer pages. Link: https://patch.msgid.link/20260309162516.2623589-18-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- include/linux/simple_ring_buffer.h | 8 +++ kernel/trace/simple_ring_buffer.c | 91 +++++++++++++++++++++++------- 2 files changed, 80 insertions(+), 19 deletions(-) diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring= _buffer.h index 2c4c0ae336bc..21aec556293e 100644 --- a/include/linux/simple_ring_buffer.h +++ b/include/linux/simple_ring_buffer.h @@ -54,4 +54,12 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *c= pu_buffer); =20 int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buff= er); =20 +int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer, + struct simple_buffer_page *bpages, + const struct ring_buffer_desc *desc, + void *(*load_page)(unsigned long va), + void (*unload_page)(void *va)); + +void simple_ring_buffer_unload_mm(struct simple_rb_per_cpu *cpu_buffer, + void (*unload_page)(void *)); #endif diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_b= uffer.c index 15df9781411b..02af2297ae5a 100644 --- a/kernel/trace/simple_ring_buffer.c +++ b/kernel/trace/simple_ring_buffer.c @@ -71,7 +71,7 @@ static void simple_bpage_reset(struct simple_buffer_page = *bpage) local_set(&bpage->page->commit, 0); } =20 -static void simple_bpage_init(struct simple_buffer_page *bpage, unsigned l= ong page) +static void simple_bpage_init(struct simple_buffer_page *bpage, void *page) { INIT_LIST_HEAD(&bpage->link); bpage->page =3D (struct buffer_data_page *)page; @@ -372,18 +372,15 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu= *cpu_buffer) } EXPORT_SYMBOL_GPL(simple_ring_buffer_reset); =20 -/** - * simple_ring_buffer_init - Init @cpu_buffer based on @desc - * @cpu_buffer: A simple_rb_per_cpu buffer to init, allocated by the calle= r. - * @bpages: Array of simple_buffer_pages, with as many elements as @desc->= nr_page_va - * @desc: A ring_buffer_desc - * - * Returns 0 on success or -EINVAL if the content of @desc is invalid - */ -int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct s= imple_buffer_page *bpages, - const struct ring_buffer_desc *desc) +int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer, + struct simple_buffer_page *bpages, + const struct ring_buffer_desc *desc, + void *(*load_page)(unsigned long va), + void (*unload_page)(void *va)) { struct simple_buffer_page *bpage =3D bpages; + int ret =3D 0; + void *page; int i; =20 /* At least 1 reader page and two pages in the ring-buffer */ @@ -392,15 +389,22 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu = *cpu_buffer, struct simple_ =20 memset(cpu_buffer, 0, sizeof(*cpu_buffer)); =20 - cpu_buffer->bpages =3D bpages; + cpu_buffer->meta =3D load_page(desc->meta_va); + if (!cpu_buffer->meta) + return -EINVAL; =20 - cpu_buffer->meta =3D (void *)desc->meta_va; memset(cpu_buffer->meta, 0, sizeof(*cpu_buffer->meta)); cpu_buffer->meta->meta_page_size =3D PAGE_SIZE; cpu_buffer->meta->nr_subbufs =3D cpu_buffer->nr_pages; =20 /* The reader page is not part of the ring initially */ - simple_bpage_init(bpage, desc->page_va[0]); + page =3D load_page(desc->page_va[0]); + if (!page) { + unload_page(cpu_buffer->meta); + return -EINVAL; + } + + simple_bpage_init(bpage, page); bpage->id =3D 0; =20 cpu_buffer->nr_pages =3D 1; @@ -410,7 +414,13 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *= cpu_buffer, struct simple_ cpu_buffer->head_page =3D bpage + 1; =20 for (i =3D 1; i < desc->nr_page_va; i++) { - simple_bpage_init(++bpage, desc->page_va[i]); + page =3D load_page(desc->page_va[i]); + if (!page) { + ret =3D -EINVAL; + break; + } + + simple_bpage_init(++bpage, page); =20 bpage->link.next =3D &(bpage + 1)->link; bpage->link.prev =3D &(bpage - 1)->link; @@ -419,6 +429,14 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *= cpu_buffer, struct simple_ cpu_buffer->nr_pages =3D i + 1; } =20 + if (ret) { + for (i--; i >=3D 0; i--) + unload_page((void *)desc->page_va[i]); + unload_page(cpu_buffer->meta); + + return ret; + } + /* Close the ring */ bpage->link.next =3D &cpu_buffer->tail_page->link; cpu_buffer->tail_page->link.prev =3D &bpage->link; @@ -426,23 +444,58 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu = *cpu_buffer, struct simple_ /* The last init'ed page points to the head page */ simple_bpage_set_head_link(bpage); =20 + cpu_buffer->bpages =3D bpages; + return 0; } -EXPORT_SYMBOL_GPL(simple_ring_buffer_init); + +static void *__load_page(unsigned long page) +{ + return (void *)page; +} + +static void __unload_page(void *page) { } =20 /** - * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion - * @cpu_buffer: A simple_rb_per_cpu that will be deleted. + * simple_ring_buffer_init - Init @cpu_buffer based on @desc + * @cpu_buffer: A simple_rb_per_cpu buffer to init, allocated by the calle= r. + * @bpages: Array of simple_buffer_pages, with as many elements as @desc->= nr_page_va + * @desc: A ring_buffer_desc + * + * Returns 0 on success or -EINVAL if the content of @desc is invalid */ -void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer) +int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct s= imple_buffer_page *bpages, + const struct ring_buffer_desc *desc) +{ + return simple_ring_buffer_init_mm(cpu_buffer, bpages, desc, __load_page, = __unload_page); +} +EXPORT_SYMBOL_GPL(simple_ring_buffer_init); + +void simple_ring_buffer_unload_mm(struct simple_rb_per_cpu *cpu_buffer, + void (*unload_page)(void *)) { + int p; + if (!simple_rb_loaded(cpu_buffer)) return; =20 simple_rb_enable_tracing(cpu_buffer, false); =20 + unload_page(cpu_buffer->meta); + for (p =3D 0; p < cpu_buffer->nr_pages; p++) + unload_page(cpu_buffer->bpages[p].page); + cpu_buffer->bpages =3D NULL; } + +/** + * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion + * @cpu_buffer: A simple_rb_per_cpu that will be deleted. + */ +void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer) +{ + return simple_ring_buffer_unload_mm(cpu_buffer, __unload_page); +} EXPORT_SYMBOL_GPL(simple_ring_buffer_unload); =20 /** --=20 2.51.0 From nobody Thu Apr 9 05:45:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 814903093DF for ; Tue, 10 Mar 2026 14:35:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; 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charset="utf-8" From: Vincent Donnefort The simple_ring_buffer implementation must remain simple enough to be used by the pKVM hypervisor. Prevent the object build if unresolved symbols are found. Link: https://patch.msgid.link/20260309162516.2623589-19-vdonnefort@google.= com Reviewed-by: Steven Rostedt (Google) Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt (Google) --- kernel/trace/Makefile | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index d106beca8d7f..3182e1bc1cf7 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -132,4 +132,20 @@ obj-$(CONFIG_TRACE_REMOTE) +=3D trace_remote.o obj-$(CONFIG_SIMPLE_RING_BUFFER) +=3D simple_ring_buffer.o obj-$(CONFIG_TRACE_REMOTE_TEST) +=3D remote_test.o =20 +# +# simple_ring_buffer is used by the pKVM hypervisor which does not have ac= cess +# to all kernel symbols. Fail the build if forbidden symbols are found. +# +UNDEFINED_ALLOWLIST :=3D memset alt_cb_patch_nops __x86 __ubsan __asan __k= asan __gcov __aeabi_unwind +UNDEFINED_ALLOWLIST +=3D __stack_chk_fail stackleak_track_stack __ref_stac= k __sanitizer +UNDEFINED_ALLOWLIST :=3D $(addprefix -e , $(UNDEFINED_ALLOWLIST)) + +quiet_cmd_check_undefined =3D NM $< + cmd_check_undefined =3D test -z "`$(NM) -u $< | grep -v $(UNDEFINED_= ALLOWLIST)`" + +$(obj)/%.o.checked: $(obj)/%.o FORCE + $(call if_changed,check_undefined) + +always-$(CONFIG_SIMPLE_RING_BUFFER) +=3D simple_ring_buffer.o.checked + libftrace-y :=3D ftrace.o --=20 2.51.0