From patchwork Sun Feb 12 15:32:50 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13137463 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 8DB1BC05027 for ; Sun, 12 Feb 2023 15:33:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229735AbjBLPdY (ORCPT ); Sun, 12 Feb 2023 10:33:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229712AbjBLPdO (ORCPT ); Sun, 12 Feb 2023 10:33:14 -0500 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 1A3D6C65D for ; Sun, 12 Feb 2023 07:33:10 -0800 (PST) Received: by mail-wm1-x349.google.com with SMTP id k17-20020a05600c1c9100b003dd41ad974bso5404279wms.3 for ; Sun, 12 Feb 2023 07:33:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=M+d4ipAHpReLmFZk9nFLE2xPZqTKQlJEwK1FQJWisIY=; b=bPDmQfdCZw8lNqkinMZjF8xpczDSiTRYQgdspyJY8Vf5QPMuk36Z0VU7JJThODDPWf vlySehWqGwFR1EG95l6sJg0Eh6UNcQx1u8uOn5KZXDA3SRdUKHzyzcjA7KmhRijKJDDk tXxtgR+W7Zw6QBTTz4E6dTH7+GHKtjGGNVqMbLGKulERjMwSDk34nPk3Qv9GFzktEY6L fhD0Rd4Dtb4w0Aa2FKG8Lpk8I2jxs797I04cwrMRIocF8nKPyUNk9Lnx6y3hm1NTOZd7 1T0e13BQBz1GCug+pcPpAOP8Sy3eQIO1ekH4D3hJrp8Y1xraoZ/HkSuEUtDS39nD5TUi mvhA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; 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=M+d4ipAHpReLmFZk9nFLE2xPZqTKQlJEwK1FQJWisIY=; b=S7sS/Clc0GwUsYJh3NCSd4onZN/6RQHSIA0cqaToFumYQvEQ6pzQYR3WwzSi673gMr PjkZFMoKGGayUTqpaL8KuuaFPex3YmTDKI7ikG63gCm62ng4jI7FDXI12zl5nihwRy2j vltnKdlBY3c6sOcjV6WLkNToFwsTA2egc5vBIQCGDugOxoJdD38CaqPsVSUoZVCg3lb7 RHdDsx854FQjiyOMMWz6jafFogNewIqgIiRMg9qD0QMj1E1MKp5p4JssyDj7Gy1lGzNT r1Xpknia5Jm91YLIhF0T81KrGVdqnHGwdE6+nh1DwwEwvqc+keCIqEHJGtr4WS0lwOMX 7K/w== X-Gm-Message-State: AO0yUKVdLZ3tzId4J9ZVCkIk8O8/lNL/hj41I04jYQtuXOn+6mWYWDnN FfUx8bXOEbmvk6dRUuElaoBi1gi7kC+90uie X-Google-Smtp-Source: AK7set9HzQqLLwTBhCUfaS347mT3tH0TTlTVjXRiHOtP9X/USfmu8A7LMFbYHs3kJctWE2Hvss1QMZLLh7Qntj8u X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:600c:1c81:b0:3db:105:85a4 with SMTP id k1-20020a05600c1c8100b003db010585a4mr1282764wms.124.1676215988772; Sun, 12 Feb 2023 07:33:08 -0800 (PST) Date: Sun, 12 Feb 2023 15:32:50 +0000 In-Reply-To: <20230212153250.1099136-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230212153250.1099136-1-vdonnefort@google.com> X-Mailer: git-send-email 2.39.1.581.gbfd45094c4-goog Message-ID: <20230212153250.1099136-3-vdonnefort@google.com> Subject: [RFC 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 not possible 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 into 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. To avoid putting to much work on the writer, the meta-page is not automatically updated. User-space must query an update before reading with another ioctl: TRACE_MMAP_IOCTL_UPDATE_META_PAGE. Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h index 0f3282fa1a94..fe3bbe02e571 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -11,4 +11,7 @@ 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 78ed5f1baa8c..e7d999499dde 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6351,7 +6351,7 @@ 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) @@ -8384,15 +8384,27 @@ 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++; @@ -8405,6 +8417,61 @@ 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; + + vma->vm_flags |= VM_DONTCOPY | VM_DONTDUMP; + vma->vm_flags &= ~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, @@ -8413,6 +8480,7 @@ 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