From patchwork Thu Dec 21 17:35:23 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13502445 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 27CAE6350B for ; Thu, 21 Dec 2023 17:35:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="MGk8JF0G" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-5caf86963ecso15969987b3.3 for ; Thu, 21 Dec 2023 09:35:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1703180132; x=1703784932; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=d/chp9iYc18PijDbo+8g07Uc+eJNKO0EynyXnVgKIzI=; b=MGk8JF0Gy+yAzKfIOl1qcxpR1QYAR0Re83l8bnDMyVBh/8TlomVFF0NSy4wfSkUcVO j6NaG0EHDk1jLjANpqMW75URhYwIlvONfgIC45SSXFsL1P2znzDJl3XX9Z0g1jQi7/CE wp59MU5TWvdZyIIhOQPaMwjTtO6/tpZgehCvDCOQ3uccQU+DqG84x6w+BM6EboD/KJZO 02XOT682/O7AsLAXBBMBS98rKzofzoBtbD0HkWdCetzcDV0XnuoEbv92KvlZibaHLIrc BM88DMP4fBkv3NaJF+bMGsNPuoc0+LwsccBnK4UUwafXIjXVnyAB64U119lmlYWH0vWa YXmw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1703180132; x=1703784932; 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=d/chp9iYc18PijDbo+8g07Uc+eJNKO0EynyXnVgKIzI=; b=NW8Ou1YoddVxt1socZhoNCeeESUfT/wwc9/JYHFhquR6jnydfBo4byNjzE70yoOMZb h86LWZv8XsWJEp64VWtqVPOvbjVJqzhbP3Y/wee/hEJSXlQu9973nevB1MINBe+ab1fN EVX1r8qwDczkqfXMYRd8235mxT2QQUSiaOuhYo7/5gD4M/kYtKz5K9qFiu3c3cIG337h +gfaht3Y1mD9dMSpHCxqYybc5c0xj0y9f3qPIZSIhXxfTE8D8JLKqyUrHWcXqmlgYr/j e+ya/U94s1lYe6eNBzB8UytShzd83Th6T1rwV6mew6JBKnIHWWqhlCEpYL7GUB708y6v 076A== X-Gm-Message-State: AOJu0Yzd11xjfW3Ejx0aRemO6KOxhN7Xa/ak5PQWBa27c+W7KKGETEqv j+CHfLRRv5bzvkYrYdrlZbGX0Nl+PcHiBZIq1V67SEQ= X-Google-Smtp-Source: AGHT+IGB3a8jB7CQe9SSOQn3k4KcYq+8FU6pZoJGtjqAyLqxHYvIbi2/5WluMi6tqcxp1EYsAAkzJIAZDlnkkWs4 X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:6902:136e:b0:dbd:7508:f527 with SMTP id bt14-20020a056902136e00b00dbd7508f527mr1087ybb.5.1703180132391; Thu, 21 Dec 2023 09:35:32 -0800 (PST) Date: Thu, 21 Dec 2023 17:35:23 +0000 In-Reply-To: <20231221173523.3015715-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20231221173523.3015715-1-vdonnefort@google.com> X-Mailer: git-send-email 2.43.0.472.g3155946c3a-goog Message-ID: <20231221173523.3015715-3-vdonnefort@google.com> Subject: [PATCH v9 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 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 is exposed via the per-CPU file trace_pipe_raw. The first element of the mapping is the meta-page. It is followed by each subbuffer constituting the ring-buffer, ordered by their unique page ID: * Meta-page -- include/uapi/linux/trace_mmap.h for a description * Subbuf ID 0 * Subbuf ID 1 ... It is therefore easy to translate a subbuf ID into an offset in the mapping: reader_id = meta->reader->id; reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size; When new data is available, the mapper must call a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to point to the next reader containing unread data. Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h index f950648b0ba9..8c49489c5867 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -26,4 +26,6 @@ struct trace_buffer_meta { __u32 meta_struct_len; /* Len of this struct */ }; +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1) + #endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 46dbe22121e9..cfeaf2cd204e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8583,15 +8583,31 @@ 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; + int err; - if (cmd) - return -ENOIOCTLCMD; + if (cmd == TRACE_MMAP_IOCTL_GET_READER) { + if (!(file->f_flags & O_NONBLOCK)) { + err = ring_buffer_wait(iter->array_buffer->buffer, + iter->cpu_file, + iter->tr->buffer_percent); + if (err) + return err; + } + return ring_buffer_map_get_reader(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++; @@ -8604,6 +8620,62 @@ 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; + 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, @@ -8612,6 +8684,7 @@ 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