From nobody Mon Feb 9 19:26:41 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 B345DC001DE for ; Fri, 28 Jul 2023 16:50:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235473AbjG1Quy (ORCPT ); Fri, 28 Jul 2023 12:50:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234945AbjG1QuS (ORCPT ); Fri, 28 Jul 2023 12:50:18 -0400 Received: from mail-wr1-x449.google.com (mail-wr1-x449.google.com [IPv6:2a00:1450:4864:20::449]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A90E59C5 for ; Fri, 28 Jul 2023 09:48:53 -0700 (PDT) Received: by mail-wr1-x449.google.com with SMTP id ffacd0b85a97d-30e6153f0eeso1202333f8f.0 for ; Fri, 28 Jul 2023 09:48:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1690562893; x=1691167693; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=ss9MUA3Tr56YAsWyllu6HM14rw2I4XzRyajq/SbgYxY=; b=4c5l0dRm/bFC3tsehp6MrNkqMUm+BOvSlEM5xvMAprLXVe3P7IyU3LOlmODS/ChG0l BHw3u9pjVmhR21N7+TXS2DdTz2M4Kyu7sm5xonA6y5RjqQLU3N2wNle1/fBkSBMSq4aI budE9554Zm4Fj2UPe2sG4I5MXtx9tQC2gIyzeE0Vi8BLBB27ADgqzuR8m+CN1vf5jce4 4UV5BCnEHTFzyT4JPcqo8IfBJgtO11Wxx5Kq6bx1hoV2FfVF8s8qKsIDCoghNn8ZdCDV Fwnd8NgicwZn1bx8Cp119wPidRYOxQlWWs8z/ZmeGTCG/oxjlIXdkTpDuLOGvSYY4Lze tiIg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690562893; x=1691167693; 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=ss9MUA3Tr56YAsWyllu6HM14rw2I4XzRyajq/SbgYxY=; b=AYd3ncVEwRE1kasmQhEnvtL3T7nRo6fPEQgGmTbsBuDGa8OqauCjUi4XA4+3fv1OT7 vTyNwxJ17fGHn8Fx9I7cJgo30lnKE3cK5c34KwH34KU2pD/GcB/zVshcU4Z7mJPxRSXR 9b9ZO/K+QU/OGroaGdh4Ip4o8tu6+AjKzLxdzXP3Jc22psMDsKGmr6AbJRHZl0pkpyR7 D1vlqZAQ6pYg7ilkfrus0pqVvYjEjzla2vrlY78WkUccer+Se8RdpRfMJo0wvJ962xq7 2itR029xaI8yaSX8RIzSX3wVbAKU8FTXHu1Gv0qYzssbLyl8KRs1Oo//66J3QwftKk+g tbYw== X-Gm-Message-State: ABy/qLbtawuLUTB/c7K25zQznvSitpr4np5cQMM1UGsCDa2gQpOxAquT W+VEO6Gz1Z8cbqY5mvBxa2NoYKjCk2gYhGBa X-Google-Smtp-Source: APBJJlE4iRbPMO0jdJvQOOvJEL7qN8hQVRczTqoiowzZ3DLigKFhhjDYpkpMbm9tFqX4bbDGpvqqXtMfjpRuEYZE X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a5d:43ce:0:b0:317:7514:100a with SMTP id v14-20020a5d43ce000000b003177514100amr23308wrr.6.1690562892607; Fri, 28 Jul 2023 09:48:12 -0700 (PDT) Date: Fri, 28 Jul 2023 17:47:54 +0100 In-Reply-To: <20230728164754.460767-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230728164754.460767-1-vdonnefort@google.com> X-Mailer: git-send-email 2.41.0.487.g6d72f3e995-goog Message-ID: <20230728164754.460767-3-vdonnefort@google.com> Subject: [PATCH v5 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 job: swap the reader with the head. This is done with a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER_PAGE. Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mma= p.h index 653176cc50bc..fd323a92cf78 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -23,4 +23,6 @@ struct ring_buffer_meta { } reader_page; }; =20 +#define TRACE_MMAP_IOCTL_GET_READER_PAGE _IO('T', 0x1) + #endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b8870078ef58..849d2d1c73fe 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6461,7 +6461,7 @@ 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) @@ -8495,15 +8495,21 @@ 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 - if (cmd) - return -ENOIOCTLCMD; + if (cmd =3D=3D TRACE_MMAP_IOCTL_GET_READER_PAGE) + return ring_buffer_map_get_reader_page(iter->array_buffer->buffer, + iter->cpu_file); + else if (cmd) + 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++; @@ -8516,6 +8522,63 @@ 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, @@ -8524,6 +8587,7 @@ 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 2.41.0.487.g6d72f3e995-goog