From patchwork Sun Apr 9 17:39:23 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13206010 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 52406C77B61 for ; Sun, 9 Apr 2023 17:39:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229622AbjDIRjm (ORCPT ); Sun, 9 Apr 2023 13:39:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229586AbjDIRje (ORCPT ); Sun, 9 Apr 2023 13:39:34 -0400 Received: from mail-ed1-x549.google.com (mail-ed1-x549.google.com [IPv6:2a00:1450:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ACC8435BC for ; Sun, 9 Apr 2023 10:39:33 -0700 (PDT) Received: by mail-ed1-x549.google.com with SMTP id x1-20020a50ba81000000b0050234a3ad75so659929ede.23 for ; Sun, 09 Apr 2023 10:39:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1681061972; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=wqRGpCqbtVC488h2OQKSqrWXyjUQrRT9sWanjh2AEc4=; b=L61O/4Racqisn/CcQLsLz24hTVM47/kWqySmywyAx04F7n968AzREOpP8feCMzqZwq j2dE9gfVX5EfVDpjchXJtg4nxpepHOAqaTYb2ukFcNUHsOGXGp019qhdHPI2A/1GQqil PFQHWuYK8zFKi3gnSs/YHt2S2fLGZAf/G+kgWAjXMNH8H1EHA5HBJUaWI2z7UsY5nCoA FkT0xkNNUHWmS2hSllA7GlHghiuKdHDAye89ZSw2iiyXP+rhGz6ke/PWFUmw2G+C50ni LNDAtsot4prlpFYk3Dv9G6YWWM6shk2rDellkwGfdE08GL+fHujgxR1tGQRS4WkRYGyQ jZIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1681061972; 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=wqRGpCqbtVC488h2OQKSqrWXyjUQrRT9sWanjh2AEc4=; b=QSVbilEYLSiqH8tru8b6chARR3s92yKbyuihb0y1TDThAArOXVyHzn4DuTN+4SyVOg GQk0OYQP1SpLSgI6gbaWvlpFrKsV0gpAlnSNkbCzRI0pNPBdglW0vXSWQJOk/lls6Omb ZkwvzJ0DnPNVUmHPlpjhM/GUPPYsP56eoP2prirC/5JKuRbb0mOY3FIeHGkCCy8nwrJk kWpAb+y3yTrFQ3SBGhdCtOTppfHc0/zkcdE2aSi7tO9rzxCgeSQQPxL0uacUpMKX6/Nj y2c/jI6dqZNkZ2jarBVOzTcq8dl6O8KUNLkoENWBK/s8FNuH253ij02iHV4uwdG/v3eA 4UXA== X-Gm-Message-State: AAQBX9cQEqv/zicDN7aMXEY+knb2yYlMSU7QRN8v5X+DeLfasQjLISBF QmKrB//W10XhyST3BP3pxnR6oL+Yak1zmeqt X-Google-Smtp-Source: AKy350ZO9BPOKGQZeu7RmWzOReHJC5wm910vzRkwdsDWBDG1NfR3U6Yj8m0HcJTG0td13mCw7ONx56F5VONFFFLG X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a17:906:cd28:b0:932:4d97:a370 with SMTP id oz40-20020a170906cd2800b009324d97a370mr2113151ejb.14.1681061972164; Sun, 09 Apr 2023 10:39:32 -0700 (PDT) Date: Sun, 9 Apr 2023 18:39:23 +0100 In-Reply-To: <20230409173923.1822455-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230409173923.1822455-1-vdonnefort@google.com> X-Mailer: git-send-email 2.40.0.577.gac1e443424-goog Message-ID: <20230409173923.1822455-3-vdonnefort@google.com> Subject: [PATCH v3 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 b89e0c8562b5..70b97c0ea888 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -21,4 +21,6 @@ struct ring_buffer_meta_header { __u32 read; /* Number of bytes read on the current 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 45551c7b4c36..8a64ca87afaf 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 == &nop_trace) return; - + tr->current_trace->enabled--; if (tr->current_trace->reset) @@ -8432,15 +8432,21 @@ 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_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++; @@ -8453,6 +8459,63 @@ 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, @@ -8461,6 +8524,7 @@ 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