1 files changed, 142 insertions, 91 deletions

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 7bd27f0e2880..a39b3c749de5 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
 #
@@ -583,13 +595,13 @@ 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
@@ -690,13 +702,13 @@ 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
@@ -837,13 +849,13 @@ 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
@@ -999,12 +1011,12 @@ 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
@@ -1114,11 +1126,11 @@ 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
@@ -1155,7 +1167,7 @@ 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);
@@ -1163,26 +1175,20 @@ 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
@@ -1193,8 +1199,8 @@ 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
@@ -1216,6 +1222,51 @@ 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)
@@ -1226,12 +1277,12 @@ 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);
 
@@ -1383,22 +1434,22 @@ 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:
@@ -1427,8 +1478,8 @@ 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:
 
@@ -1451,8 +1502,8 @@ 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:
 
@@ -1549,7 +1600,7 @@ 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
@@ -1561,12 +1612,12 @@ 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
@@ -1577,7 +1628,7 @@ 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
 
@@ -1597,7 +1648,7 @@ 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:
 
@@ -1618,7 +1669,7 @@ 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
@@ -1644,17 +1695,17 @@ 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
@@ -1677,7 +1728,7 @@ 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:
 
@@ -1767,13 +1818,13 @@ 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
@@ -1809,7 +1860,7 @@ 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.
@@ -1817,18 +1868,18 @@ 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
 
 -----------