From patchwork Fri Mar 17 14:33:10 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13179119 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 76A21C6FD1D for ; Fri, 17 Mar 2023 14:33:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231238AbjCQOdn (ORCPT ); Fri, 17 Mar 2023 10:33:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231152AbjCQOdi (ORCPT ); Fri, 17 Mar 2023 10:33:38 -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 9F8E7E4C5D for ; Fri, 17 Mar 2023 07:33:33 -0700 (PDT) Received: by mail-wm1-x349.google.com with SMTP id l18-20020a05600c4f1200b003ed35ab903aso3952032wmq.6 for ; Fri, 17 Mar 2023 07:33:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1679063612; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=pr8i0Eumz09pFpMEBVzLFDV1F++dQdI0hyhxEAp2n3w=; b=KFFpGv1i3Q3hEABcr9gwon1e9ZOOii+a9nok8Xz6VJHQXlZj8a4ilUYyQ7HMnuhkCI sXZLVNB42WAB9R7e4mMHVa9IZOWnDXuNH+2j9OKDAHzVLPmvvD6GIRnvO3NL+LPmoXb7 CuYqX6HtBJEl7yOy8tE3CbgH2a9QuAhgQH0TMKy6gIwD8vuHiQY14lGwrbFvySHqxjcW UHWAke4bMF7QCgim7nTrat4IpktRIS4roz/VIcQX5Tyx5Mc3q8mmJStRrFEcodzEy9VI XUqcI0Leb2W5ruN5ngLNBSm4rP1RDU/TYfcc9QEzXLb0+IXTjftKOL6d3GVh+lQTWdfp ZTSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679063612; 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=pr8i0Eumz09pFpMEBVzLFDV1F++dQdI0hyhxEAp2n3w=; b=0OSedUOCcbp5oUD7O31/tcVH2zo71YBux7T1GEzixzVyAahWMf4Z1eh38b0zdsEv5+ 2u/p3jfW7AjmZyCtabdwP7Xue46inAc6xNOoviBIaKpGG/HYnu7tytcJ1IdyZWchMeX0 mo2bhhyNZvoo80cPSuiCDQB5R9kvFx+IPKvTTg9V2nxMS7NxP6yW7NQ16vrmAxgzxMa0 KdH6c/7wLSZolsS6fiJrVCvCYYoURjm5AXtQT9YpRHpc6qk3f4emApnpwssIkl0cEqIk /l2N2/+CdBcxddee3GilEF1PhuJRpwjY45ychhlLeSTYw6l1m/WNRJLlMDjQC/ZThrSi GLpA== X-Gm-Message-State: AO0yUKXvXXk3aEM2L51xJVHz45qwkp5q/RFPXiExsFNjdd1syxn50HYK nSrl5PZjpIiFXgSmrkKsbERw/nmV5o9AszEh X-Google-Smtp-Source: AK7set/+ZPVsiYqB7Hdp5WNTZma1qHm7dbiDdmEBcxtiq5xxh7zeGKnvdJNfz8Sgi+ddXtHaCz11zbRlVfE7ArBN X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:adf:efc1:0:b0:2cf:e74f:c5b1 with SMTP id i1-20020adfefc1000000b002cfe74fc5b1mr653973wrp.7.1679063612090; Fri, 17 Mar 2023 07:33:32 -0700 (PDT) Date: Fri, 17 Mar 2023 14:33:10 +0000 In-Reply-To: <20230317143310.1604700-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230317143310.1604700-1-vdonnefort@google.com> X-Mailer: git-send-email 2.40.0.rc1.284.g88254d51c5-goog Message-ID: <20230317143310.1604700-3-vdonnefort@google.com> Subject: [PATCH 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 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_mmap.h index b5caed17a066..24bcec754a35 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -21,4 +21,7 @@ struct ring_buffer_meta_page { __u32 data_pages[]; }; +#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..51d06a2a7545 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 +8432,27 @@ 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; + 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; + /* + * 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 +8465,60 @@ 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; + + get_page(page); + vmf->page = page; + + 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 +8527,7 @@ 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