From nobody Fri Dec 26 13:26:53 2025 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F05E224B41 for ; Fri, 5 Jan 2024 09:48:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="1lrzoXGC" Received: by mail-yb1-f201.google.com with SMTP id 3f1490d57ef6-dbdb46770d7so2065333276.1 for ; Fri, 05 Jan 2024 01:48:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1704448080; x=1705052880; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=d/chp9iYc18PijDbo+8g07Uc+eJNKO0EynyXnVgKIzI=; b=1lrzoXGCnJFvsELNSb+8V8v6buZvlCPDiG7gjszmqMsWo+V4rkXjWVUnVsx2sZKTGJ sbP9WMuU1JTZeJnFAFh6uJo5HIm6n+0t13mVwxfFpkfUi7Yygh7D2mlRzeMvc/VKAeW4 fAT0FYQv/GW0LPbVvHaOu9/o8mFd1uJ7rwfN+JaQxN+HrjvNbM+tHD5J4Y6RS2mEkybN SaFylMhFn+bIwQbNB3pxscqS+EeibHxHGHz+TOExYLYmWdKXiQyHnOBQedjtrhAsr685 450DaKeAnuUlmh9uo3xMTPPb6l+vg3lhbgpazQEo2PeDJjYy90Ns5ykSYYs48kIHGRd7 oH2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704448080; x=1705052880; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=d/chp9iYc18PijDbo+8g07Uc+eJNKO0EynyXnVgKIzI=; b=XJbumlO0VxxGm8GsD5KVD07d44G3La1j2HaM4p2eAeEH37WoIdxZR5t0c7dww85r46 KChPleMQb6jzReQ9zuRv+OEPDCxADfliGHN/rdmlXO1FHSpzMzqivnyolcgyNcD8eOlE iUYlEOQEFYWK2q0frlJkPc/VLcJlw52shvCqt8f/1NEo4x3osI5gAZd0QVA+DiuCqwxB k7g8jjUrRIbO/Mj+JmS1kygokQVFgUwTeXWWpQ79s27jbQP3T2BjGxbET2Vd0l6T0379 Jow7ED+V3a9qib1bW3WuoDGpPqhla+QQXJzR/n6rbZrGfrd3Z19PAuNbcDSDxiRfSaVD 9bWw== X-Gm-Message-State: AOJu0Yy69EwkNa2g7JzqG9RUZHpj63KgnUyBsk+C4rtEBoQdq/n3IgMU AKbTVh4rA21G/kzLlmtV6fqwFiO+cPa6K8hTiGiP+ys= X-Google-Smtp-Source: AGHT+IGqgJzLxvsE/UVML+foQwlWKr4XAk7ifQHuueX1WxCLsxVxp2uDLH4O0EyYxpEHa6z4eFWlt7dut2YHFTQV X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a25:bb11:0:b0:db7:dce9:76cd with SMTP id z17-20020a25bb11000000b00db7dce976cdmr723549ybg.9.1704448079979; Fri, 05 Jan 2024 01:47:59 -0800 (PST) Date: Fri, 5 Jan 2024 09:47:29 +0000 In-Reply-To: <20240105094729.2363579-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240105094729.2363579-1-vdonnefort@google.com> X-Mailer: git-send-email 2.43.0.472.g3155946c3a-goog Message-ID: <20240105094729.2363579-3-vdonnefort@google.com> Subject: [PATCH v10 2/2] tracing: Allow user-space mapping of the ring-buffer From: Vincent Donnefort To: rostedt@goodmis.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: mhiramat@kernel.org, mathieu.desnoyers@efficios.com, kernel-team@android.com, Vincent Donnefort Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, user-space extracts data from the ring-buffer via splice, which is handy for storage or network sharing. However, due to splice limitations, it is imposible to do real-time analysis without a copy. A solution for that problem is to let the user-space map the ring-buffer directly. The mapping is exposed via the per-CPU file trace_pipe_raw. The first element of the mapping is the meta-page. It is followed by each subbuffer constituting the ring-buffer, ordered by their unique page ID: * Meta-page -- include/uapi/linux/trace_mmap.h for a description * Subbuf ID 0 * Subbuf ID 1 ... It is therefore easy to translate a subbuf ID into an offset in the mapping: reader_id =3D meta->reader->id; reader_offset =3D meta->meta_page_size + reader_id * meta->subbuf_size; When new data is available, the mapper must call a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to point to the next reader containing unread data. Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mma= p.h index f950648b0ba9..8c49489c5867 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -26,4 +26,6 @@ struct trace_buffer_meta { __u32 meta_struct_len; /* Len of this struct */ }; =20 +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1) + #endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 46dbe22121e9..cfeaf2cd204e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8583,15 +8583,31 @@ tracing_buffers_splice_read(struct file *file, loff= _t *ppos, return ret; } =20 -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waite= rs */ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, uns= igned long arg) { struct ftrace_buffer_info *info =3D file->private_data; struct trace_iterator *iter =3D &info->iter; + int err; =20 - if (cmd) - return -ENOIOCTLCMD; + if (cmd =3D=3D TRACE_MMAP_IOCTL_GET_READER) { + if (!(file->f_flags & O_NONBLOCK)) { + err =3D ring_buffer_wait(iter->array_buffer->buffer, + iter->cpu_file, + iter->tr->buffer_percent); + if (err) + return err; + } =20 + return ring_buffer_map_get_reader(iter->array_buffer->buffer, + iter->cpu_file); + } else if (cmd) { + return -ENOTTY; + } + + /* + * An ioctl call with cmd 0 to the ring buffer file will wake up all + * waiters + */ mutex_lock(&trace_types_lock); =20 iter->wait_index++; @@ -8604,6 +8620,62 @@ static long tracing_buffers_ioctl(struct file *file,= unsigned int cmd, unsigned return 0; } =20 +static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf) +{ + struct ftrace_buffer_info *info =3D vmf->vma->vm_file->private_data; + struct trace_iterator *iter =3D &info->iter; + vm_fault_t ret =3D VM_FAULT_SIGBUS; + struct page *page; + + page =3D ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file, + vmf->pgoff); + if (!page) + return ret; + + get_page(page); + vmf->page =3D page; + vmf->page->mapping =3D vmf->vma->vm_file->f_mapping; + vmf->page->index =3D vmf->pgoff; + + return 0; +} + +static void tracing_buffers_mmap_close(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info =3D vma->vm_file->private_data; + struct trace_iterator *iter =3D &info->iter; + + ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file); +} + +static void tracing_buffers_mmap_open(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info =3D vma->vm_file->private_data; + struct trace_iterator *iter =3D &info->iter; + + WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file)); +} + +static const struct vm_operations_struct tracing_buffers_vmops =3D { + .open =3D tracing_buffers_mmap_open, + .close =3D tracing_buffers_mmap_close, + .fault =3D tracing_buffers_mmap_fault, +}; + +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *= vma) +{ + struct ftrace_buffer_info *info =3D filp->private_data; + struct trace_iterator *iter =3D &info->iter; + + if (vma->vm_flags & VM_WRITE) + return -EPERM; + + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE); + vma->vm_ops =3D &tracing_buffers_vmops; + + return ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file); +} + static const struct file_operations tracing_buffers_fops =3D { .open =3D tracing_buffers_open, .read =3D tracing_buffers_read, @@ -8612,6 +8684,7 @@ static const struct file_operations tracing_buffers_f= ops =3D { .splice_read =3D tracing_buffers_splice_read, .unlocked_ioctl =3D tracing_buffers_ioctl, .llseek =3D no_llseek, + .mmap =3D tracing_buffers_mmap, }; =20 static ssize_t --=20 2.43.0.472.g3155946c3a-goog