[lttng-dev] [PATCH] Expose kernel tracer to user-space (version 5)
Francis Giraldeau
francis.giraldeau at gmail.com
Mon Jul 2 09:47:27 EDT 2012
By writing to the file /proc/lttng, a user-space application creates a
kernel event. The event's payload is by default UTF-8 text, but any data
can be written, up to 1024 bytes. Null-character is optional and is not
enforced. The event uses sequence for space efficiency and to store any
data as payload.
The feature is enabled when both lttng-uevent and lttng-probe-uevent are
loaded. The lttng-abi module exports a register function and includes a wrapper
for lttng_fops write. This is required since struct file_operations must be
const.
Module unload must be prevented while lttng-uevent is being used.
rcu_synchronized() is call on module unload, and thus rcu_read_lock() can be
used to force waiting until the critical section is over.
Signed-off-by: Francis Giraldeau <francis.giraldeau at gmail.com>
---
instrumentation/events/lttng-module/uevent.h | 33 +++++++++++++++
lttng-abi.c | 42 +++++++++++++++++++
lttng-abi.h | 4 ++
probes/Makefile | 2 +
probes/lttng-probe-uevent.c | 36 ++++++++++++++++
probes/lttng-uevent.c | 58 ++++++++++++++++++++++++++
6 files changed, 175 insertions(+)
create mode 100644 instrumentation/events/lttng-module/uevent.h
create mode 100644 probes/lttng-probe-uevent.c
create mode 100644 probes/lttng-uevent.c
diff --git a/instrumentation/events/lttng-module/uevent.h b/instrumentation/events/lttng-module/uevent.h
new file mode 100644
index 0000000..f67d901
--- /dev/null
+++ b/instrumentation/events/lttng-module/uevent.h
@@ -0,0 +1,33 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM uevent
+
+#if !defined(UEVENT_H_) || defined(TRACE_HEADER_MULTI_READ)
+#define UEVENT_H_
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(lttng_uevent,
+
+ TP_PROTO(const char *str, size_t len),
+
+ TP_ARGS(str, len),
+
+ /*
+ * Uses sequence to hold variable size data, by default considered
+ * as text. Null-terminal character is optional and is not enforced.
+ */
+ TP_STRUCT__entry(
+ __dynamic_array_text(char, text, len)
+ ),
+
+ TP_fast_assign(
+ tp_memcpy_dyn_from_user(text, str)
+ ),
+
+ TP_printk("")
+)
+
+#endif /* UEVENT_H_ */
+
+/* This part must be outside protection */
+#include "../../../probes/define_trace.h"
diff --git a/lttng-abi.c b/lttng-abi.c
index 26a02ed..0de79ab 100644
--- a/lttng-abi.c
+++ b/lttng-abi.c
@@ -51,6 +51,11 @@
#include "lttng-tracer.h"
/*
+ * Required data structure to support lttng-probe-uevent
+ */
+static write_ops_t lttng_uevent_handler;
+
+/*
* This is LTTng's own personal way to create a system call as an external
* module. We use ioctl() on /proc/lttng.
*/
@@ -252,9 +257,46 @@ long lttng_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
}
}
+/*
+ * lttng_uevent_set_handler - set handler functions for uevent
+ */
+
+void lttng_uevent_set_handler(write_ops_t handler)
+{
+ lttng_uevent_handler = handler;
+}
+EXPORT_SYMBOL_GPL(lttng_uevent_set_handler);
+
+/*
+ * lttng_write_uevent - expose kernel tracer to user-space
+ *
+ * The handler function is protected with rcu_read_lock() to prevent the
+ * module to be unloaded while the tracepoint is being used. It assumes that
+ * rcu_synchronize() is called on module unload.
+ */
+
+static
+ssize_t lttng_write_uevent(struct file *file, const char __user *ubuf,
+ size_t count, loff_t *fpos)
+{
+ int ret;
+ write_ops_t handler;
+
+ rcu_read_lock();
+ handler = rcu_dereference(lttng_uevent_handler);
+ if (unlikely(handler == NULL)) {
+ rcu_read_unlock();
+ return -ENOSYS;
+ }
+ ret = handler(file, ubuf, count, fpos);
+ rcu_read_unlock();
+ return ret;
+}
+
static const struct file_operations lttng_fops = {
.owner = THIS_MODULE,
.unlocked_ioctl = lttng_ioctl,
+ .write = lttng_write_uevent,
#ifdef CONFIG_COMPAT
.compat_ioctl = lttng_ioctl,
#endif
diff --git a/lttng-abi.h b/lttng-abi.h
index dc230d8..1f3847c 100644
--- a/lttng-abi.h
+++ b/lttng-abi.h
@@ -27,6 +27,10 @@
#define LTTNG_KERNEL_SYM_NAME_LEN 256
+typedef ssize_t (*write_ops_t) (struct file *, const char __user *, size_t,
+ loff_t *);
+void lttng_uevent_set_handler(write_ops_t handler);
+
enum lttng_kernel_instrumentation {
LTTNG_KERNEL_TRACEPOINT = 0,
LTTNG_KERNEL_KPROBE = 1,
diff --git a/probes/Makefile b/probes/Makefile
index 698a9c9..a895e60 100644
--- a/probes/Makefile
+++ b/probes/Makefile
@@ -14,6 +14,8 @@ obj-m += lttng-probe-sched.o
obj-m += lttng-probe-irq.o
obj-m += lttng-probe-signal.o
obj-m += lttng-probe-timer.o
+obj-m += lttng-probe-uevent.o
+obj-m += lttng-uevent.o
obj-m += lttng-probe-statedump.o
diff --git a/probes/lttng-probe-uevent.c b/probes/lttng-probe-uevent.c
new file mode 100644
index 0000000..90abb5e
--- /dev/null
+++ b/probes/lttng-probe-uevent.c
@@ -0,0 +1,36 @@
+/*
+ * probes/lttng-probe-uevent.c
+ *
+ * Expose kernel tracer to user-space through /proc/lttng
+ *
+ * Copyright (C) 2009-2012 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>
+
+/*
+ * Create lttng_uevent tracepoint probes.
+ */
+#define LTTNG_PACKAGE_BUILD
+#define CREATE_TRACE_POINTS
+#define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module
+
+#include "../instrumentation/events/lttng-module/uevent.h"
+
+MODULE_LICENSE("GPL and additional rights");
+MODULE_AUTHOR("Mathieu Desnoyers <mathieu.desnoyers at efficios.com>");
+MODULE_DESCRIPTION("LTTng uevent probes");
diff --git a/probes/lttng-uevent.c b/probes/lttng-uevent.c
new file mode 100644
index 0000000..7b4bffc
--- /dev/null
+++ b/probes/lttng-uevent.c
@@ -0,0 +1,58 @@
+/*
+ * probes/lttng-uevent.c
+ *
+ * Expose kernel tracer to user-space through /proc/lttng
+ *
+ * Copyright (C) 2012 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 "../lttng-abi.h"
+
+/* include our own uevent tracepoint */
+#include "../instrumentation/events/lttng-module/uevent.h"
+DEFINE_TRACE(lttng_uevent);
+
+#define LTTNG_UEVENT_SIZE 1024
+
+ssize_t uevent_write_handler(struct file *file, const char __user *ubuf,
+ size_t count, loff_t *fpos)
+{
+ if (count > LTTNG_UEVENT_SIZE)
+ count = LTTNG_UEVENT_SIZE;
+
+ trace_lttng_uevent(ubuf, count);
+ return count;
+}
+
+static int __init lttng_probe_uevent_init(void)
+{
+ lttng_uevent_set_handler(uevent_write_handler);
+ return 0;
+}
+
+static void __exit lttng_probe_uevent_exit(void)
+{
+ lttng_uevent_set_handler(NULL);
+}
+
+module_init(lttng_probe_uevent_init);
+module_exit(lttng_probe_uevent_exit);
+
+MODULE_LICENSE("GPL and additional rights");
+MODULE_AUTHOR("Mathieu Desnoyers <mathieu.desnoyers at efficios.com>");
+MODULE_DESCRIPTION("LTTng kernel event from user-space");
--
1.7.9.5
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