From mboxrd@z Thu Jan 1 00:00:00 1970 From: mathieu.desnoyers@polymtl.ca (Mathieu Desnoyers) Date: Mon, 15 Dec 2008 18:10:40 -0500 Subject: [ltt-dev] [PATCH] Simple LTTng userspace events through debugfs Message-ID: <20081215231040.GA5936@Krystal> Hi, I looked at kmemtrace and noticed that the presence of a debugfs "marker" file, which lets userspace write events into the trace buffers. So I just did the same with a /debugfs/ltt/write_event file in LTTng. This should be OK for userspace tracing which does not require high throughput. It allows userspace to write a string up to 4095-bytes long into the channel named "userspace", event named "event". This new feature is available in LTTng 0.68 (for kernel 2.6.27.9). For the curious, I provide the patch applied on top of the LTTng tree below. Mathieu LTTng userspace event Add userspace event support to LTTng. Simply has to write to : /debugfs/ltt/write_event E.g. : echo "Error X happened !" > /debugfs/ltt/write_event (assuming debugfs is mounted under /debugfs) Todo : Maybe use ltt_relay_user_blocking to block if channel is full rather than losing an event ? Be careful about effect of stopped tracing on userspace... Signed-off-by: Mathieu Desnoyers --- ltt/Kconfig | 9 +++ ltt/Makefile | 1 ltt/ltt-userspace-event.c | 120 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 130 insertions(+) Index: linux-2.6-lttng/ltt/Kconfig =================================================================== --- linux-2.6-lttng.orig/ltt/Kconfig 2008-12-15 16:18:04.000000000 -0500 +++ linux-2.6-lttng/ltt/Kconfig 2008-12-15 16:18:08.000000000 -0500 @@ -125,6 +125,15 @@ config LTT_DEBUG_EVENT_SIZE help Tracer-internal option to help debugging event type encoding problems. +config LTT_USERSPACE_EVENT + tristate "Support logging events from userspace" + depends on LTT_TRACER + depends on LTT_TRACEPROBES + default m + help + This option lets userspace write text events in + /debugfs/ltt/write_event. + config LTT_VMCORE bool "Support trace extraction from crash dump" default y Index: linux-2.6-lttng/ltt/Makefile =================================================================== --- linux-2.6-lttng.orig/ltt/Makefile 2008-12-15 16:18:04.000000000 -0500 +++ linux-2.6-lttng/ltt/Makefile 2008-12-15 16:18:08.000000000 -0500 @@ -5,6 +5,7 @@ obj-$(CONFIG_MARKERS) += ltt-channels.o obj-$(CONFIG_LTT) += ltt-core.o obj-$(CONFIG_LTT_TRACER) += ltt-tracer.o +obj-$(CONFIG_LTT_USERSPACE_EVENT) += ltt-userspace-event.o obj-$(CONFIG_LTT_RELAY) += ltt-relay.o obj-$(CONFIG_LTT_RELAY_LOCKED) += ltt-relay-locked.o obj-$(CONFIG_LTT_RELAY_ALLOC) += ltt-relay-alloc.o Index: linux-2.6-lttng/ltt/ltt-userspace-event.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-2.6-lttng/ltt/ltt-userspace-event.c 2008-12-15 17:19:33.000000000 -0500 @@ -0,0 +1,120 @@ +/* + * Copyright (C) 2008 Mathieu Desnoyers + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + */ + +#include +#include +#include +#include +#include +#include + +#include "probes/ltt-type-serializer.h" + +#define LTT_WRITE_EVENT_FILE "write_event" + +DEFINE_MARKER(userspace, event, "string %s"); +static struct dentry *ltt_event_file; + +/** + * write_event: write a userspace string into the trace stream + * @file: file pointer + * @user_buf: user string + * @count: length to copy, including the final NULL + * @ppos: unused + * + * Copy at most a 4095-bytes string into a trace event, in channel "userspace", + * event "event". Returns -E2BIG if string is larger than 4095kB. Last byte is + * kept for NULL character. + * On success, returns the number of bytes copied (without NULL character). + */ +static ssize_t write_event(struct file *file, const char __user *user_buf, + size_t count, loff_t *ppos) +{ + struct marker *marker; + char *page; + int ret; + + if (count > PAGE_SIZE - 1) { + ret = -E2BIG; + goto string_out; + } + page = (char *)__get_free_page(GFP_TEMPORARY); + if (!page) { + ret = -ENOMEM; + goto string_out; + } + ret = copy_from_user(page, user_buf, count); + if (ret) { + ret = -EFAULT; + goto string_err; + } + page[count] = '\0'; + + marker = &GET_MARKER(userspace, event); + ltt_specialized_trace(marker, marker->single.probe_private, + page, count + 1, sizeof(char)); + ret = count; +string_err: + free_page((unsigned long)page); +string_out: + return ret; +} + +static struct file_operations ltt_userspace_operations = { + .write = write_event, +}; + +static int __init ltt_userspace_init(void) +{ + struct dentry *ltt_root_dentry; + int err = 0; + + ltt_root_dentry = get_ltt_root(); + if (!ltt_root_dentry) { + err = -ENOENT; + goto err_no_root; + } + + ltt_event_file = debugfs_create_file(LTT_WRITE_EVENT_FILE, + S_IWUGO, + ltt_root_dentry, + NULL, + <t_userspace_operations); + if (IS_ERR(ltt_event_file) || !ltt_event_file) { + printk(KERN_ERR + "ltt_userspace_init: failed to create file %s\n", + LTT_WRITE_EVENT_FILE); + err = -EPERM; + goto err_no_file; + } +err_no_file: +err_no_root: + return err; +} + +static void __exit ltt_userspace_exit(void) +{ + debugfs_remove(ltt_event_file); +} + +module_init(ltt_userspace_init); +module_exit(ltt_userspace_exit); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Mathieu Desnoyers "); +MODULE_DESCRIPTION("Linux Trace Toolkit Userspace Event"); -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68