Re: [RFC V2 PATCH]debugfs:Fix terminology inconsistency of dir name to mount debugfs filesystem.

From: GeunSik Lim
Date: Sat May 30 2009 - 07:22:07 EST

On Sat, May 30, 2009 at 6:38 PM, GeunSik Lim <leemgs1@xxxxxxxxx> wrote:
>> Also, since I'm the most picky about this, you may want to remove the
>> ftrace files from the patch and move it to another patch. That way the
> I am not think that you are the most picky about this. I like your advice and
> review about my proposal for consensus.
>> owners of the other files can ack them and get those changes in. When we
>> have something for ftrace, I'll give my ack. But lets not hold up the
>> other changes because of me ;-)
>>
> Don't care. Hope it helps. ;-)
> I will modify Âftrace files from the patch according to your advice.

I updated ftrace related contents according to Steven's help like belows.
If I misunderstood wrongly, Please correct me.
Thanks.

* About ftrace.txt file/
---
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index fd9a3e6..caaf5d9 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
+
+For quicker access to that directory you may want to make a soft link to
+it:

- # mkdir /debug
- # mount -t debugfs nodev /debug
+ ln -s /sys/kernel/debug /debug

-( Note: it is more common to mount at /sys/kernel/debug, but for
- simplicity this document will use /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(find_debugfs("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
@@ -1202,11 +1208,57 @@ something like this simple program:

#include <stdio.h>
#include <stdlib.h>
+#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

+#define _STR(x) #x
+#define STR(x) _STR(x)
+#define MAX_PATH 256
+
+const char *find_debugfs(char *file_name)
+{
+ static char debugfs[MAX_PATH+1];
+ static int debugfs_found;
+ char type[100];
+ FILE *fp;
+ int size;
+
+ 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;
+
+ size = MAX_PATH - strlen(debugfs);
+ strncat(debugfs, "/tracing/", size);
+
+ size = MAX_PATH - strlen(debugfs);
+ strncat(debugfs, file_name, size);
+
+ return debugfs;
+}
+
int main (int argc, char **argv)
{
if (argc < 1)
@@ -1217,12 +1269,12 @@ int main (int argc, char **argv)
char line[64];
int s;

- ffd = open("/debug/tracing/current_tracer", O_WRONLY);
+ ffd = open(find_debugfs("current_tracer"), O_WRONLY);
if (ffd < 0)
exit(-1);
write(ffd, "nop", 3);

- fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY);
+ fd = open(find_debugfs("set_ftrace_pid"), O_WRONLY);
s = sprintf(line, "%d\n", getpid());
write(fd, line, s);

@@ -1374,22 +1426,22 @@ 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 +1470,8 @@ 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 +1494,8 @@ 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 +1592,7 @@ 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 +1604,12 @@ 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 +1620,7 @@ 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 +1640,7 @@ 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 +1661,7 @@ 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 +1687,17 @@ 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 +1720,7 @@ 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 +1810,13 @@ 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 +1852,7 @@ 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 +1860,18 @@ 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@xxxxxxxxxxx
leemgs@xxxxxxxxx , leemgs1@xxxxxxxxx

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