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

On Sat, 30 May 2009, GeunSik Lim wrote:

> Thanks your advice. I agree with your reply about this patch.
> I updated contents that you advised like belows.
> If I mistake, Please correct me.
>
> And, I also need your review about below 2 contents in the ftrace.txt file.
>
> Thanks,
> GeunSik Lim.
>
>
> 1)
> @@ -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("/sys/kernel/debug/tracing/tracing_enabled", O_WRONLY);
> [...]
> if (condition_hit()) {
> write(trace_fd, "0", 1);
> @@ -1154,26 +1166,23 @@ int main(int argc, char *argv[]) {
> [...]
> }
>
>
> @@ -1217,12 +1226,12 @@ int main (int argc, char **argv)
> char line[64];
> int s;
>
> - ffd = open("/debug/tracing/current_tracer", O_WRONLY);
> + ffd =
> open("/sys/kernel/debug/tracing/current_tracer", O_WRONLY);
> if (ffd < 0)
> exit(-1);
> write(ffd, "nop", 3);
>
> - fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY);
> + fd = open("/sys/kernel/debug/tracing/set_ftrace_pid",
> O_WRONLY);
> s = sprintf(line, "%d\n", getpid());
> write(fd, line, s);
> -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
> +Note: Here we hard coded the path name. A search through /proc/mounts may
> be needed to find where the debugfs file-system is mounted.

Here's the function I use:

#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;
}

This might be a good idea to show it. This is the most robust since it
does not hard code the debugfs directory.

>
> 2)
> More details can be found in the source code, in the
> -kernel/tracing/*.c files.
> +kernel/trace/*.c files
>
>
>
> * about ftrace.txt file
> ---
> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
> index fd9a3e6..790199b 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

Please remove the "./", it is also distracting. We state that we "cd" to
the location. "cat trace_options" is good enough.

Same for the all the others below.

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
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 ;-)

-- Steve

> 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("/sys/kernel/debug/tracing/tracing_enabled", O_WRONLY);
> [...]
> if (condition_hit()) {
> write(trace_fd, "0", 1);
> @@ -1154,26 +1166,23 @@ 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
> +Note: Here we hard coded the path name. 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 +1193,8 @@ 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
> @@ -1217,12 +1226,12 @@ int main (int argc, char **argv)
> char line[64];
> int s;
>
> - ffd = open("/debug/tracing/current_tracer", O_WRONLY);
> + ffd =
> open("/sys/kernel/debug/tracing/current_tracer", O_WRONLY);
> if (ffd < 0)
> exit(-1);
> write(ffd, "nop", 3);
>
> - fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY);
> + fd = open("/sys/kernel/debug/tracing/set_ftrace_pid",
> O_WRONLY);
> s = sprintf(line, "%d\n", getpid());
> write(fd, line, s);
>
> @@ -1374,22 +1383,22 @@ 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 +1427,8 @@ 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 +1451,8 @@ 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 +1549,7 @@ 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 +1561,12 @@ 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 +1577,7 @@ 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 +1597,7 @@ 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 +1618,7 @@ 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 +1644,17 @@ 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 +1677,7 @@ 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 +1767,13 @@ 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 +1809,7 @@ 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.
> @@ -1808,21 +1817,21 @@ 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
>
> ---
>
> On Sat, May 30, 2009 at 1:48 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> >
> >
> > On Sat, 30 May 2009, GeunSik Lim wrote:
> >
> >>
> >>
> >> Dear Greg and Steen,
> >>
> >> Thanks your advices and opinions about a confusion according to
> >> too many mount directory names for debugfs. I made rfc v2 patch file again like belows.
> >> Can I hear your advices about below patch contents?.
> >>
> >> * ref:
> >> http://groups.google.com/group/linux.kernel/browse_thread/thread/c34e386587979340/dc52317f888e78b6?#dc52317f888e78b6
> >>
> >>
> >> Regards,
> >> GeunSik Lim.
> >>
> >> Subject: [PATCH]   Fix terminology inconsistency of dir name to mount debugfs filesystem.
> >>
> >>       Many developers use "/debug/" or "/debugfs/ directory name to mount
> >>       debugfs filesystem for ftrace according to
> >>       ./Documentation/tracers/ftrace.txt file.
> >>
> >>       And, three directory names(ex:/debug/, /debugfs/, /sys/kernel/debug/) is
> >>       existed in kernel source like ftrace, DRM, Wireless, Network[sky2]files
> >>       to mount debugfs filesystem.
> >>
> >>       debugfs means debug filesystem for debugging easy to use by greg kroah
> >>       hartman. "/sys/kernel/debug/" name is suitable as directory name
> >>       of debugfs filesystem.
> >>       -debugfs related reference: http://lwn.net/Articles/115405/
> >
> > Note, LWN has an update this week:
> >
> >  http://lwn.net/Articles/334546/
> >
> > But it currently is subscriber only. Others would need to either buy a
> > subscription (plug) or wait a week for it to become open.
> >
> > Still for some aspects, just having "debugfs" without the leading "/"
> > might just be self explanatory. We can assume the user already knows where
> > debugfs is mounted.
> >
> > -- Steve
> >
> >
> >>
> >>       Fix inconsistency of directory name to mount debugfs filesystem.
> >>
> >>          Signed-off-by: GeunSik Lim <geunsik.lim@samsung.com>
> >>          Acked-By: Inaky Perez-Gonzalez <inaky@linux.intel.com>
> >>          CC: Greg KH <greg@kroah.com>
> >>          CC: Steven Rostedt <rostedt@goodmis.org>
> >>          CC: linux-kernel <linux-kernel@vger.kernel.org>
> >
>
>
>
> --
> Regards,
> GeunSik Lim ( SAMSUNG ELECTRONICS)
> Blog : http://blog.naver.com/invain/
> e-Mail: geunsik.lim@samsung.com
> leemgs@gmail.com , leemgs1@gmail.com
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
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>
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