From nobody Mon Feb 9 20:30:17 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7FDFCC6FD1C for ; Wed, 22 Mar 2023 10:27:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230245AbjCVK1I (ORCPT ); Wed, 22 Mar 2023 06:27:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230191AbjCVK1B (ORCPT ); Wed, 22 Mar 2023 06:27:01 -0400 Received: from mail-wm1-x349.google.com (mail-wm1-x349.google.com [IPv6:2a00:1450:4864:20::349]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1691D5F200 for ; Wed, 22 Mar 2023 03:26:54 -0700 (PDT) Received: by mail-wm1-x349.google.com with SMTP id q21-20020a05600c46d500b003ee570749f7so840102wmo.7 for ; Wed, 22 Mar 2023 03:26:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1679480812; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=wZ9f1BjLJkOFx0USqHh1WH8B1brZoQG0BbTDKoggwrY=; b=Ejct3CO8JsVUJdMjCYvwmgl3ejKMv9zBdrexMkafvTz3btw8DlF3TGWS8WHdbD8VEI 31NyEqErGFRnD56yw1XbEP0lsaAIMPQrI6HHtM4iO7xtaaUlOXNjGvFnKAV0/v5sDKsO BR82aJxENZcGtR4b0IxJE7lNVYuj98cYWUDUjv6x+Lf+MWz0z3y4BSv0EFigZ4MwHail KrgaMmTEh28dPxKa9ZeWsFmiFhjE61UW2NpoCRzbF9Z455wG0DqMKe5uQvAXFzUdkFNd nhD9lhGHM1InvN23fvM1Fg7BG04GOR9oZyyNpbbUaAejQ5hIgzn/pIjC5soMlOhwNn/V l+og== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679480812; 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=wZ9f1BjLJkOFx0USqHh1WH8B1brZoQG0BbTDKoggwrY=; b=eq+tw9hUtuKXXIr5kXY5aW8Vx9/YexYDhgLZgnwkeufdLsk2KBFGIQ4LMATqdi5SmZ DM0cORUZsYEPNgXMtAMaT6I9GhhF+UgJlz6X7BASPu7O/uAMjIUS1h2xKA5Ms1shG9/3 ASJNnn+Ixka83tU+OiMhjK4y0oApuy0VTFlC9kT6vFn8nhOJBKhyrUKXzyv4tZs0lULT N7PMeljocohdS7607Z5JQiH1KtnsMauWrVXGQCGLrHR8Zix1Tz/QRGcSOOnv3uSuZzrH m0euM2ZPrLMIT/GKf78mQkR4KtUQbTzCfCXEJ1TT25/31OTQLqiuPDp/V2E8tHNdox87 3mEA== X-Gm-Message-State: AO0yUKUPLF6g7m2y07VomrRmfV5byQV8W/E7wLvysoJagcMs/5/sR2x1 ahRRxvuLyoMlLknkgojHOigB+25TCLhUVJL1 X-Google-Smtp-Source: AK7set/jzeu/HzOtAk02LcoJyMCJOw0BLZu0S3oh+aO1r7aJsqhV5v9IafmheLKGw4WyyABB5MuVYzel/M/1+w+c X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a5d:534e:0:b0:2c5:557a:59b2 with SMTP id t14-20020a5d534e000000b002c5557a59b2mr1138478wrv.12.1679480812653; Wed, 22 Mar 2023 03:26:52 -0700 (PDT) Date: Wed, 22 Mar 2023 10:22:44 +0000 In-Reply-To: <20230322102244.3239740-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230322102244.3239740-1-vdonnefort@google.com> X-Mailer: git-send-email 2.40.0.rc1.284.g88254d51c5-goog Message-ID: <20230322102244.3239740-3-vdonnefort@google.com> Subject: [PATCH v2 2/2] tracing: Allow user-space mapping of the ring-buffer From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: kernel-team@android.com, Vincent Donnefort Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 exposed via the per-CPU file trace_pipe_raw. The first page is the meta-page and is followed by each page of the ring-buffer, ordered by their unique page ID. It is therefore easy to translate a page-ID to an offset in the mapping. * Meta-page -- include/uapi/linux/trace_mmap.h for a description * Page ID 0 * Page ID 1 ... The mapper must then do what use to be the kernel jobs: swap the reader with the head. This is done with a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER_PAGE. Entries, pages_touched and overrun fields are automatically updated by the writer. Only readers keep the head page field updated. An additional ioctl TRACE_MMAP_IOCTL_UPDATE_META_PAGE allows to query that update, enabling non-consuming read from userspace. Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mma= p.h index 7794314a80e9..c33adea0aa84 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -22,4 +22,7 @@ struct ring_buffer_meta_page_header { __u32 data_start; /* offset within the meta page */ }; =20 +#define TRACE_MMAP_IOCTL_GET_READER_PAGE _IO('T', 0x1) +#define TRACE_MMAP_IOCTL_UPDATE_META_PAGE _IO('T', 0x2) + #endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 45551c7b4c36..65251a28f2a9 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6399,7 +6399,7 @@ static void tracing_set_nop(struct trace_array *tr) { if (tr->current_trace =3D=3D &nop_trace) return; -=09 + tr->current_trace->enabled--; =20 if (tr->current_trace->reset) @@ -8432,15 +8432,27 @@ 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; =20 + switch (cmd) { + case TRACE_MMAP_IOCTL_GET_READER_PAGE: + return ring_buffer_get_reader_page(iter->array_buffer->buffer, + iter->cpu_file); + case TRACE_MMAP_IOCTL_UPDATE_META_PAGE: + return ring_buffer_update_meta_page(iter->array_buffer->buffer, + iter->cpu_file); + } + if (cmd) - return -ENOIOCTLCMD; + return -ENOTTY; =20 + /* + * 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++; @@ -8453,6 +8465,63 @@ 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; + + vmf->page =3D page; + + get_page(vmf->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, @@ -8461,6 +8530,7 @@ 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 2.40.0.rc1.284.g88254d51c5-goog