[lttng-dev] [PATCH] LTTng logger ABI
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Mon Feb 17 16:11:52 EST 2014
Add a user-space ABI (new file /proc/lttng-logger) to lttng-modules
which can be written into by any user on the system. The content is
saved into the kernel trace stream into the "lttng_logger" kernel event.
The content of a single write is written into an lttng_logger event.
The write count is truncated to 1024 bytes (if larger), which is much
smaller than the smallest subbuffer size available (4096 bytes). This
ensures all written data makes it into the active tracing buffers.
Example use:
lttng-sessiond -d # (as root)
lttng create
lttng enable-event -k lttng_logger
lttng start
echo -n "this is a test" > /proc/lttng-logger
lttng stop
lttng view
Example result:
[17:00:04.251970425] (+179.750663203) thinkos lttng_logger: { cpu_id = 3 }, { _msg_length = 14, msg = "this is a test" }
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
CC: Karim Yaghmour <karim.yaghmour at opersys.com>
---
Makefile | 3 +-
instrumentation/events/lttng-module/lttng.h | 24 +++++
lttng-events.c | 7 ++
lttng-events.h | 3 +
probes/lttng.c | 134 +++++++++++++++++++++++++++
5 files changed, 170 insertions(+), 1 deletion(-)
create mode 100644 instrumentation/events/lttng-module/lttng.h
create mode 100644 probes/lttng.c
diff --git a/Makefile b/Makefile
index a9d1cb1..a4c602f 100644
--- a/Makefile
+++ b/Makefile
@@ -20,7 +20,8 @@ lttng-tracer-objs := lttng-events.o lttng-abi.o \
lttng-context-vpid.o lttng-context-tid.o \
lttng-context-vtid.o lttng-context-ppid.o \
lttng-context-vppid.o lttng-calibrate.o \
- lttng-context-hostname.o wrapper/random.o
+ lttng-context-hostname.o wrapper/random.o \
+ probes/lttng.o
obj-m += lttng-statedump.o
lttng-statedump-objs := lttng-statedump-impl.o wrapper/irqdesc.o \
diff --git a/instrumentation/events/lttng-module/lttng.h b/instrumentation/events/lttng-module/lttng.h
new file mode 100644
index 0000000..c2ddf8d
--- /dev/null
+++ b/instrumentation/events/lttng-module/lttng.h
@@ -0,0 +1,24 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM lttng
+
+#if !defined(_TRACE_LTTNG_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_LTTNG_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(lttng_logger,
+ TP_PROTO(const char __user *text, size_t len),
+ TP_ARGS(text, len),
+ TP_STRUCT__entry(
+ __dynamic_array_text(char, msg, len)
+ ),
+ TP_fast_assign(
+ tp_memcpy_dyn_from_user(msg, text)
+ ),
+ TP_printk("")
+)
+
+#endif /* _TRACE_LTTNG_H */
+
+/* This part must be outside protection */
+#include "../../../probes/define_trace.h"
diff --git a/lttng-events.c b/lttng-events.c
index 0512a3f..ff28c9a 100644
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -1261,7 +1261,13 @@ static int __init lttng_events_init(void)
ret = lttng_abi_init();
if (ret)
goto error_abi;
+ ret = lttng_logger_init();
+ if (ret)
+ goto error_logger;
return 0;
+
+error_logger:
+ lttng_abi_exit();
error_abi:
kmem_cache_destroy(event_cache);
return ret;
@@ -1273,6 +1279,7 @@ static void __exit lttng_events_exit(void)
{
struct lttng_session *session, *tmpsession;
+ lttng_logger_exit();
lttng_abi_exit();
list_for_each_entry_safe(session, tmpsession, &sessions, list)
lttng_session_destroy(session);
diff --git a/lttng-events.h b/lttng-events.h
index 6b39304..aeb2a6b 100644
--- a/lttng-events.h
+++ b/lttng-events.h
@@ -429,6 +429,9 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
}
#endif
+int lttng_logger_init(void);
+void lttng_logger_exit(void);
+
extern int lttng_statedump_start(struct lttng_session *session);
#ifdef CONFIG_KPROBES
diff --git a/probes/lttng.c b/probes/lttng.c
new file mode 100644
index 0000000..8025687
--- /dev/null
+++ b/probes/lttng.c
@@ -0,0 +1,134 @@
+/*
+ * lttng.c
+ *
+ * LTTng logger ABI
+ *
+ * Copyright (C) 2008-2014 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <linux/module.h>
+#include <linux/tracepoint.h>
+#include <linux/uaccess.h>
+#include <linux/gfp.h>
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+#include <linux/slab.h>
+#include <linux/mm.h>
+#include "../wrapper/vmalloc.h"
+#include "../lttng-events.h"
+
+#define TP_MODULE_NOAUTOLOAD
+#define LTTNG_PACKAGE_BUILD
+#define CREATE_TRACE_POINTS
+#define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module
+#define TRACE_INCLUDE_FILE lttng
+
+#include "../instrumentation/events/lttng-module/lttng.h"
+
+/* Events written through logger are truncated at 1024 bytes */
+#define LTTNG_LOGGER_COUNT_MAX 1024
+#define LTTNG_LOGGER_FILE "lttng-logger"
+
+static struct proc_dir_entry *lttng_logger_dentry;
+
+/**
+ * lttng_logger_write - write a userspace string into the trace system
+ * @file: file pointer
+ * @user_buf: user string
+ * @count: length to copy
+ * @ppos: file position
+ *
+ * Copy a userspace string into a trace event named "lttng:logger".
+ * Copies at most @count bytes into the event "msg" dynamic array.
+ * Truncates the count at LTTNG_LOGGER_COUNT_MAX. Returns the number of
+ * bytes copied from the source.
+ * Return -1 on error, with EFAULT errno.
+ */
+static
+ssize_t lttng_logger_write(struct file *file, const char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ unsigned int nr_pages = 1, i;
+ unsigned long uaddr = (unsigned long) user_buf;
+ struct page *pages[2];
+ ssize_t written;
+ int ret;
+
+ /* Truncate count */
+ if (unlikely(count > LTTNG_LOGGER_COUNT_MAX))
+ count = LTTNG_LOGGER_COUNT_MAX;
+
+ /* How many pages are we dealing with ? */
+ if (unlikely((uaddr & PAGE_MASK) != ((uaddr + count) & PAGE_MASK)))
+ nr_pages = 2;
+
+ /* Pin userspace pages */
+ ret = get_user_pages_fast(uaddr, nr_pages, 0, pages);
+ if (unlikely(ret < nr_pages)) {
+ if (ret > 0) {
+ BUG_ON(ret != 1);
+ put_page(pages[0]);
+ }
+ written = -EFAULT;
+ goto end;
+ }
+
+ /* Trace the event */
+ trace_lttng_logger(user_buf, count);
+ written = count;
+ *ppos += written;
+
+ for (i = 0; i < nr_pages; i++)
+ put_page(pages[i]);
+end:
+ return written;
+}
+
+static const struct file_operations lttng_logger_operations = {
+ .write = lttng_logger_write,
+};
+
+int __init lttng_logger_init(void)
+{
+ int ret = 0;
+
+ wrapper_vmalloc_sync_all();
+ lttng_logger_dentry = proc_create_data(LTTNG_LOGGER_FILE,
+ S_IRUGO | S_IWUGO, NULL,
+ <tng_logger_operations, NULL);
+ if (!lttng_logger_dentry) {
+ printk(KERN_ERR "Error creating LTTng logger file\n");
+ ret = -ENOMEM;
+ goto error;
+ }
+ ret = __lttng_events_init__lttng();
+ if (ret)
+ goto error_events;
+ return ret;
+
+error_events:
+ remove_proc_entry("lttng-logger", NULL);
+error:
+ return ret;
+}
+
+void __exit lttng_logger_exit(void)
+{
+ __lttng_events_exit__lttng();
+ if (lttng_logger_dentry)
+ remove_proc_entry("lttng-logger", NULL);
+}
--
1.7.10.4
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