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Message-ID: <49b7c2350905300817s6d14cd2dy87cb93cf7d7774b@mail.gmail.com>
Date: Sun, 31 May 2009 00:17:45 +0900
From: GeunSik Lim <leemgs1@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Greg KH <greg@...ah.com>,
linux-kernel <linux-kernel@...r.kernel.org>, trivial@...nel.org,
balagi@...tmail.de, bgamari@...il.com, Ingo Molnar <mingo@...e.hu>,
inaky.perez-gonzalez@...el.com
Subject: Re: [RFC V2 PATCH]debugfs:Fix terminology inconsistency of dir name
to mount debugfs filesystem.
On Sat, May 30, 2009 at 10:44 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> You need to make two functions. One to find the debugfs and one to add the
> file. The "debugfs_found" will make the function return just the first
> file_name every time. Something like this: (remove the file_name from
> find_debugfs).
>
> const char *tracing_file(const char *file_name)
> {
> static char trace_file[MAX_PATH+1];
>
> snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);
>
> return trace_file;
> }
>
> The above is not thread safe, but is OK for non threaded programs.
Thanks.
I modified pseudo code using tracing_file function that you sent.
* ftrace.txt info after modification.
---
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index fd9a3e6..05f8378 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -7,7 +7,6 @@ Copyright 2008 Red Hat Inc.
(dual licensed under the GPL v2)
Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton,
John Kacur, and David Teigland.
-
Written for: 2.6.28-rc2
Introduction
@@ -33,13 +32,26 @@ The File System
Ftrace uses the debugfs file system to hold the control files as
well as the files to display output.
-To mount the debugfs system:
+When debugfs is configured into the kernel (which selecting any ftrace
+option will do) the directory /sys/kernel/debug will be created. To mount
+this directory, you can add to your /etc/fstab file:
+
+ debugfs /sys/kernel/debug debugfs defaults 0 0
+
+Or you can mount it at run time with:
+
+ mount -t debugfs nodev /sys/kernel/debug
- # mkdir /debug
- # mount -t debugfs nodev /debug
+For quicker access to that directory you may want to make a soft link to
+it:
-( Note: it is more common to mount at /sys/kernel/debug, but for
- simplicity this document will use /debug)
+ ln -s /sys/kernel/debug /debug
+
+Any selected ftrace option will also create a directory called tracing
+within the debugfs. The rest of the document will assume that you are in
+the ftrace directory (cd /sys/kernel/debug/tracing) and will only concentrate
+on the files within that directory and not distract from the content with
+the extended "/sys/kernel/debug/tracing" path name.
That's it! (assuming that you have ftrace configured into your kernel)
@@ -389,18 +401,18 @@ trace_options
The trace_options file is used to control what gets printed in
the trace output. To see what is available, simply cat the file:
- cat /debug/tracing/trace_options
+ cat trace_options
print-parent nosym-offset nosym-addr noverbose noraw nohex nobin \
noblock nostacktrace nosched-tree nouserstacktrace nosym-userobj
To disable one of the options, echo in the option prepended with
"no".
- echo noprint-parent > /debug/tracing/trace_options
+ echo noprint-parent > trace_options
To enable an option, leave off the "no".
- echo sym-offset > /debug/tracing/trace_options
+ echo sym-offset > trace_options
Here are the available options:
@@ -476,11 +488,11 @@ sched_switch
This tracer simply records schedule switches. Here is an example
of how to use it.
- # echo sched_switch > /debug/tracing/current_tracer
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo sched_switch > current_tracer
+ # echo 1 > tracing_enabled
# sleep 1
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/trace
+ # echo 0 > tracing_enabled
+ # cat trace
# tracer: sched_switch
#
@@ -574,13 +586,13 @@ new trace is saved.
To reset the maximum, echo 0 into tracing_max_latency. Here is
an example:
- # echo irqsoff > /debug/tracing/current_tracer
- # echo 0 > /debug/tracing/tracing_max_latency
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo irqsoff > current_tracer
+ # echo 0 > tracing_max_latency
+ # echo 1 > tracing_enabled
# ls -ltr
[...]
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/latency_trace
+ # echo 0 > tracing_enabled
+ # cat latency_trace
# tracer: irqsoff
#
irqsoff latency trace v1.1.5 on 2.6.26
@@ -681,13 +693,13 @@ Like the irqsoff tracer, it records the maximum
latency for
which preemption was disabled. The control of preemptoff tracer
is much like the irqsoff tracer.
- # echo preemptoff > /debug/tracing/current_tracer
- # echo 0 > /debug/tracing/tracing_max_latency
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo preemptoff > current_tracer
+ # echo 0 > tracing_max_latency
+ # echo 1 > tracing_enabled
# ls -ltr
[...]
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/latency_trace
+ # echo 0 > tracing_enabled
+ # cat latency_trace
# tracer: preemptoff
#
preemptoff latency trace v1.1.5 on 2.6.26-rc8
@@ -828,13 +840,13 @@ tracer.
Again, using this trace is much like the irqsoff and preemptoff
tracers.
- # echo preemptirqsoff > /debug/tracing/current_tracer
- # echo 0 > /debug/tracing/tracing_max_latency
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo preemptirqsoff > current_tracer
+ # echo 0 > tracing_max_latency
+ # echo 1 > tracing_enabled
# ls -ltr
[...]
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/latency_trace
+ # echo 0 > tracing_enabled
+ # cat latency_trace
# tracer: preemptirqsoff
#
preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
@@ -990,12 +1002,12 @@ slightly differently than we did with the
previous tracers.
Instead of performing an 'ls', we will run 'sleep 1' under
'chrt' which changes the priority of the task.
- # echo wakeup > /debug/tracing/current_tracer
- # echo 0 > /debug/tracing/tracing_max_latency
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo wakeup > current_tracer
+ # echo 0 > tracing_max_latency
+ # echo 1 > tracing_enabled
# chrt -f 5 sleep 1
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/latency_trace
+ # echo 0 > tracing_enabled
+ # cat latency_trace
# tracer: wakeup
#
wakeup latency trace v1.1.5 on 2.6.26-rc8
@@ -1105,11 +1117,11 @@ can be done from the debug file system. Make sure the
ftrace_enabled is set; otherwise this tracer is a nop.
# sysctl kernel.ftrace_enabled=1
- # echo function > /debug/tracing/current_tracer
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo function > current_tracer
+ # echo 1 > tracing_enabled
# usleep 1
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/trace
+ # echo 0 > tracing_enabled
+ # cat trace
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
@@ -1146,7 +1158,7 @@ int trace_fd;
[...]
int main(int argc, char *argv[]) {
[...]
- trace_fd = open("/debug/tracing/tracing_enabled", O_WRONLY);
+ trace_fd = open(tracing_file("tracing_enabled"), O_WRONLY);
[...]
if (condition_hit()) {
write(trace_fd, "0", 1);
@@ -1154,26 +1166,20 @@ int main(int argc, char *argv[]) {
[...]
}
-Note: Here we hard coded the path name. The debugfs mount is not
-guaranteed to be at /debug (and is more commonly at
-/sys/kernel/debug). For simple one time traces, the above is
-sufficent. For anything else, a search through /proc/mounts may
-be needed to find where the debugfs file-system is mounted.
-
Single thread tracing
---------------------
-By writing into /debug/tracing/set_ftrace_pid you can trace a
+By writing into set_ftrace_pid you can trace a
single thread. For example:
-# cat /debug/tracing/set_ftrace_pid
+# cat set_ftrace_pid
no pid
-# echo 3111 > /debug/tracing/set_ftrace_pid
-# cat /debug/tracing/set_ftrace_pid
+# echo 3111 > set_ftrace_pid
+# cat set_ftrace_pid
3111
-# echo function > /debug/tracing/current_tracer
-# cat /debug/tracing/trace | head
+# echo function > current_tracer
+# cat trace | head
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
@@ -1184,8 +1190,8 @@ no pid
yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base
<-hrtimer_try_to_cancel
yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
-# echo -1 > /debug/tracing/set_ftrace_pid
-# cat /debug/tracing/trace |head
+# echo -1 > set_ftrace_pid
+# cat trace |head
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
@@ -1207,6 +1213,51 @@ something like this simple program:
#include <fcntl.h>
#include <unistd.h>
+#define _STR(x) #x
+#define STR(x) _STR(x)
+#define MAX_PATH 256
+
+const char *find_debugfs(void)
+{
+ static char debugfs[MAX_PATH+1];
+ static int debugfs_found;
+ char type[100];
+ FILE *fp;
+
+ if (debugfs_found)
+ return debugfs;
+
+ if ((fp = fopen("/proc/mounts","r")) == NULL) {
+ perror("/proc/mounts");
+ return NULL;
+ }
+
+ while (fscanf(fp, "%*s %"
+ STR(MAX_PATH)
+ "s %99s %*s %*d %*d\n",
+ debugfs, type) == 2) {
+ if (strcmp(type, "debugfs") == 0)
+ break;
+ }
+ fclose(fp);
+
+ if (strcmp(type, "debugfs") != 0) {
+ fprintf(stderr, "debugfs not mounted");
+ return NULL;
+ }
+
+ debugfs_found = 1;
+
+ return debugfs;
+}
+
+const char *tracing_file(const char *file_name)
+{
+ static char trace_file[MAX_PATH+1];
+ snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);
+ return trace_file;
+}
+
int main (int argc, char **argv)
{
if (argc < 1)
@@ -1217,12 +1268,12 @@ int main (int argc, char **argv)
char line[64];
int s;
- ffd = open("/debug/tracing/current_tracer", O_WRONLY);
+ ffd = open(tracing_file("current_tracer"), O_WRONLY);
if (ffd < 0)
exit(-1);
write(ffd, "nop", 3);
- fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY);
+ fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
s = sprintf(line, "%d\n", getpid());
write(fd, line, s);
@@ -1374,22 +1425,22 @@ want, depending on your needs.
tracing_cpu_mask file) or you might sometimes see unordered
function calls while cpu tracing switch.
- hide: echo nofuncgraph-cpu > /debug/tracing/trace_options
- show: echo funcgraph-cpu > /debug/tracing/trace_options
+ hide: echo nofuncgraph-cpu > trace_options
+ show: echo funcgraph-cpu > trace_options
- The duration (function's time of execution) is displayed on
the closing bracket line of a function or on the same line
than the current function in case of a leaf one. It is default
enabled.
- hide: echo nofuncgraph-duration > /debug/tracing/trace_options
- show: echo funcgraph-duration > /debug/tracing/trace_options
+ hide: echo nofuncgraph-duration > trace_options
+ show: echo funcgraph-duration > trace_options
- The overhead field precedes the duration field in case of
reached duration thresholds.
- hide: echo nofuncgraph-overhead > /debug/tracing/trace_options
- show: echo funcgraph-overhead > /debug/tracing/trace_options
+ hide: echo nofuncgraph-overhead > trace_options
+ show: echo funcgraph-overhead > trace_options
depends on: funcgraph-duration
ie:
@@ -1418,8 +1469,8 @@ want, depending on your needs.
- The task/pid field displays the thread cmdline and pid which
executed the function. It is default disabled.
- hide: echo nofuncgraph-proc > /debug/tracing/trace_options
- show: echo funcgraph-proc > /debug/tracing/trace_options
+ hide: echo nofuncgraph-proc > trace_options
+ show: echo funcgraph-proc > trace_options
ie:
@@ -1442,8 +1493,8 @@ want, depending on your needs.
system clock since it started. A snapshot of this time is
given on each entry/exit of functions
- hide: echo nofuncgraph-abstime > /debug/tracing/trace_options
- show: echo funcgraph-abstime > /debug/tracing/trace_options
+ hide: echo nofuncgraph-abstime > trace_options
+ show: echo funcgraph-abstime > trace_options
ie:
@@ -1540,7 +1591,7 @@ listed in:
available_filter_functions
- # cat /debug/tracing/available_filter_functions
+ # cat available_filter_functions
put_prev_task_idle
kmem_cache_create
pick_next_task_rt
@@ -1552,12 +1603,12 @@ mutex_lock
If I am only interested in sys_nanosleep and hrtimer_interrupt:
# echo sys_nanosleep hrtimer_interrupt \
- > /debug/tracing/set_ftrace_filter
- # echo ftrace > /debug/tracing/current_tracer
- # echo 1 > /debug/tracing/tracing_enabled
+ > set_ftrace_filter
+ # echo ftrace > current_tracer
+ # echo 1 > tracing_enabled
# usleep 1
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/trace
+ # echo 0 > tracing_enabled
+ # cat trace
# tracer: ftrace
#
# TASK-PID CPU# TIMESTAMP FUNCTION
@@ -1568,7 +1619,7 @@ If I am only interested in sys_nanosleep and
hrtimer_interrupt:
To see which functions are being traced, you can cat the file:
- # cat /debug/tracing/set_ftrace_filter
+ # cat set_ftrace_filter
hrtimer_interrupt
sys_nanosleep
@@ -1588,7 +1639,7 @@ Note: It is better to use quotes to enclose the
wild cards,
otherwise the shell may expand the parameters into names
of files in the local directory.
- # echo 'hrtimer_*' > /debug/tracing/set_ftrace_filter
+ # echo 'hrtimer_*' > set_ftrace_filter
Produces:
@@ -1609,7 +1660,7 @@ Produces:
Notice that we lost the sys_nanosleep.
- # cat /debug/tracing/set_ftrace_filter
+ # cat set_ftrace_filter
hrtimer_run_queues
hrtimer_run_pending
hrtimer_init
@@ -1635,17 +1686,17 @@ To append to the filters, use '>>'
To clear out a filter so that all functions will be recorded
again:
- # echo > /debug/tracing/set_ftrace_filter
- # cat /debug/tracing/set_ftrace_filter
+ # echo > set_ftrace_filter
+ # cat set_ftrace_filter
#
Again, now we want to append.
- # echo sys_nanosleep > /debug/tracing/set_ftrace_filter
- # cat /debug/tracing/set_ftrace_filter
+ # echo sys_nanosleep > set_ftrace_filter
+ # cat set_ftrace_filter
sys_nanosleep
- # echo 'hrtimer_*' >> /debug/tracing/set_ftrace_filter
- # cat /debug/tracing/set_ftrace_filter
+ # echo 'hrtimer_*' >> set_ftrace_filter
+ # cat set_ftrace_filter
hrtimer_run_queues
hrtimer_run_pending
hrtimer_init
@@ -1668,7 +1719,7 @@ hrtimer_init_sleeper
The set_ftrace_notrace prevents those functions from being
traced.
- # echo '*preempt*' '*lock*' > /debug/tracing/set_ftrace_notrace
+ # echo '*preempt*' '*lock*' > set_ftrace_notrace
Produces:
@@ -1758,13 +1809,13 @@ the effect on the tracing is different. Every read from
trace_pipe is consumed. This means that subsequent reads will be
different. The trace is live.
- # echo function > /debug/tracing/current_tracer
- # cat /debug/tracing/trace_pipe > /tmp/trace.out &
+ # echo function > current_tracer
+ # cat trace_pipe > /tmp/trace.out &
[1] 4153
- # echo 1 > /debug/tracing/tracing_enabled
+ # echo 1 > tracing_enabled
# usleep 1
- # echo 0 > /debug/tracing/tracing_enabled
- # cat /debug/tracing/trace
+ # echo 0 > tracing_enabled
+ # cat trace
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
@@ -1800,7 +1851,7 @@ number listed is the number of entries that can
be recorded per
CPU. To know the full size, multiply the number of possible CPUS
with the number of entries.
- # cat /debug/tracing/buffer_size_kb
+ # cat buffer_size_kb
1408 (units kilobytes)
Note, to modify this, you must have tracing completely disabled.
@@ -1808,18 +1859,18 @@ To do that, echo "nop" into the current_tracer. If the
current_tracer is not set to "nop", an EINVAL error will be
returned.
- # echo nop > /debug/tracing/current_tracer
- # echo 10000 > /debug/tracing/buffer_size_kb
- # cat /debug/tracing/buffer_size_kb
+ # echo nop > current_tracer
+ # echo 10000 > buffer_size_kb
+ # cat buffer_size_kb
10000 (units kilobytes)
The number of pages which will be allocated is limited to a
percentage of available memory. Allocating too much will produce
an error.
- # echo 1000000000000 > /debug/tracing/buffer_size_kb
+ # echo 1000000000000 > buffer_size_kb
-bash: echo: write error: Cannot allocate memory
- # cat /debug/tracing/buffer_size_kb
+ # cat buffer_size_kb
85
---
--
Regards,
GeunSik Lim ( SAMSUNG ELECTRONICS)
Blog : http://blog.naver.com/invain/
e-Mail: geunsik.lim@...sung.com
leemgs@...il.com , leemgs1@...il.com
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