From patchwork Tue Jun 13 08:35:13 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13278148 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 7344AC77B7A for ; Tue, 13 Jun 2023 08:35:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241302AbjFMIf3 (ORCPT ); Tue, 13 Jun 2023 04:35:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241295AbjFMIf3 (ORCPT ); Tue, 13 Jun 2023 04:35:29 -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 C9761D2 for ; Tue, 13 Jun 2023 01:35:27 -0700 (PDT) Received: by mail-wm1-x349.google.com with SMTP id 5b1f17b1804b1-3f7f2d9a660so20176045e9.2 for ; Tue, 13 Jun 2023 01:35:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1686645326; x=1689237326; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=idAAT7Bu38PyLwdgVJzIw2LhWBOsmVWg1cRqwUSMs3c=; b=iC7aqWyh5guGQ8w2RsWJlR+Gt6z8z/IRLsbShnWPEnE/6BuKjltRc1ZvvLoTOUJ+sA e86rcGyhDEbWTQJSFyuVxpwbbgroNhEXexSnAM15DpvMypfzOdRCEdUHqkiTHh4AIBrL TwnMMbGyE3zdWjj0vfWS+ZiVhR6d2+wXIkW6DlRhey3s5ejNhnCFL2vEah3VzWnaBFyx 3P3w0mPaL/Q77VfhMpP3+hMorNDJa83pAVSNIsvrwP8OXNn3zpoHAO+xsI4HcftbtZDU 8J1U43RiKQFPEy5pS8n7hFQ2PGg6FUpvtylW7xC5uyFjth3BhP/9Ry7JaRr8lWfMW325 +kvg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1686645326; x=1689237326; 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=idAAT7Bu38PyLwdgVJzIw2LhWBOsmVWg1cRqwUSMs3c=; b=h3k5sB3fCAgLscWo+TIqd4SRx11+2kStMHZcM36GCRbtYCw0FDCcQHwCM5WRqF/Wie 1614YqPyPK3ilQFYrv/U+aWhdQpr/LW4F00kdScdJcv1pMq/FKib0ZbAMCK0XNJq73wR ibz3LKdHoiHHv1TgjBD3ifYauUl/8PJMC+CaTA/rLLp/A+jLiAyMRhb1WmfXEHqu+160 ZuKU7wYk1w0xi6TG6ap2+AvTe7rOMsOA/w23RhdfFmQ+e1xvSGG5SFYaDw/EPvVBghDg CxbJoKPswTimIoaZ4K+3p1edWAlfyJ+UzgAx7XHl4MiwQ/nW5kWGQzGaz9D8lRTpXNpZ wdpA== X-Gm-Message-State: AC+VfDxd3BS1/qE6KXykbUPUk4SPj/5rOaPWASSJlmlLMDkfaYXw+t3g XdCij0DndqasKllyaDqV/i3w5ZgScl6t7o/1 X-Google-Smtp-Source: ACHHUZ6BB9LQNmvz3OBHDcP4izKCFJjELfYij7NbhEc05xqwReS9Wmy2mk3JHK18tWhu6KubN1Z6Ux1zlRcxdG9v X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a1c:750a:0:b0:3f7:38dd:5ea8 with SMTP id o10-20020a1c750a000000b003f738dd5ea8mr1901891wmc.8.1686645326337; Tue, 13 Jun 2023 01:35:26 -0700 (PDT) Date: Tue, 13 Jun 2023 09:35:13 +0100 In-Reply-To: <20230613083513.3312612-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230613083513.3312612-1-vdonnefort@google.com> X-Mailer: git-send-email 2.41.0.162.gfafddb0af9-goog Message-ID: <20230613083513.3312612-3-vdonnefort@google.com> Subject: [PATCH v4 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-trace-kernel@vger.kernel.org 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_mmap.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; }; +#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 64a4dde073ef..ccc0e1dd7d0d 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6432,7 +6432,7 @@ static void tracing_set_nop(struct trace_array *tr) { if (tr->current_trace == &nop_trace) return; - + tr->current_trace->enabled--; if (tr->current_trace->reset) @@ -8465,15 +8465,21 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, return ret; } -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { struct ftrace_buffer_info *info = file->private_data; struct trace_iterator *iter = &info->iter; - if (cmd) - return -ENOIOCTLCMD; + if (cmd == 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; + /* + * An ioctl call with cmd 0 to the ring buffer file will wake up all + * waiters + */ mutex_lock(&trace_types_lock); iter->wait_index++; @@ -8486,6 +8492,63 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned return 0; } +static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf) +{ + struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data; + struct trace_iterator *iter = &info->iter; + vm_fault_t ret = VM_FAULT_SIGBUS; + struct page *page; + + page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file, + vmf->pgoff); + if (!page) + return ret; + + vmf->page = page; + + get_page(vmf->page); + vmf->page->mapping = vmf->vma->vm_file->f_mapping; + vmf->page->index = vmf->pgoff; + + return 0; +} + +static void tracing_buffers_mmap_close(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = vma->vm_file->private_data; + struct trace_iterator *iter = &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 = vma->vm_file->private_data; + struct trace_iterator *iter = &info->iter; + + WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file)); +} + +static const struct vm_operations_struct tracing_buffers_vmops = { + .open = tracing_buffers_mmap_open, + .close = tracing_buffers_mmap_close, + .fault = tracing_buffers_mmap_fault, +}; + +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = filp->private_data; + struct trace_iterator *iter = &info->iter; + + if (vma->vm_flags & VM_WRITE) + return -EPERM; + + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE); + vma->vm_ops = &tracing_buffers_vmops; + + return ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file); +} + static const struct file_operations tracing_buffers_fops = { .open = tracing_buffers_open, .read = tracing_buffers_read, @@ -8494,6 +8557,7 @@ static const struct file_operations tracing_buffers_fops = { .splice_read = tracing_buffers_splice_read, .unlocked_ioctl = tracing_buffers_ioctl, .llseek = no_llseek, + .mmap = tracing_buffers_mmap, }; static ssize_t