Re: [PATCH 5/5] perf tools: Enhance parsing events tracepoint error output

[Jiri Olsa <jolsa@redhat.com>]

On Thu, Sep 10, 2015 at 04:00:30PM +0900, Namhyung Kim wrote:
> On Mon, Sep 07, 2015 at 10:38:07AM +0200, Jiri Olsa wrote:
> > Enhancing parsing events tracepoint error output. Adding
> > more verbose output when the tracepoint is not found or
> > the tracing event path cannot be access.
> > 
> >   $ sudo perf record -e sched:sched_krava ls
> >   event syntax error: 'sched:sched_krava'
> >                        \___ unknown tracepoint
> > 
> >   Error:  File /sys/kernel/debug/tracing//tracing/events/sched/sched_krava not found.
> >   Hint:   Perhaps this kernel misses some CONFIG_ setting to enable this feature?.
> > 
> >   Run 'perf list' for a list of valid events
> >   ...
> > 
> >   $ perf record -e sched:sched_krava ls
> >   event syntax error: 'sched:sched_krava'
> >                        \___ can't access trace events
> > 
> >   Error:  No permissions to read /sys/kernel/debug/tracing//tracing/events/sched/sched_krava
> >   Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'
> 
> What about tracefs?  On my system, tracefs is mounted on
> /sys/kernel/debug/tracing thus I cannot access trace events after
> remounting debugfs with mode=755.

right, patch below keeps the actual mount and
display proper info.. could you please try?

> 
> Also, IIRC tracepoint events adds PERF_SAMPLE_RAW bit automatically,
> and it requires perf_event_paranoid being -1 for non-root user, right?

there's related error message when you try to open the
tracepoint, the whole session is like:


[jolsa@krava perf]$ ./perf record -e sched:sched_switch ls
event syntax error: 'sched:sched_switch'
                     \___ can't access trace events

Error:  No permissions to read /sys/kernel/debug/tracing/events/sched/sched_switch
Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'

Run 'perf list' for a list of valid events

 usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    -e, --event <event>   event selector. use 'perf list' to list available events
[jolsa@krava perf]$ sudo mount -o remount,mode=755 /sys/kernel/debug/tracing
[jolsa@krava perf]$ ./perf record -e sched:sched_switch ls
Error:
You may not have permission to collect stats.
Consider tweaking /proc/sys/kernel/perf_event_paranoid:
 -1 - Not paranoid at all
  0 - Disallow raw tracepoint access for unpriv
  1 - Disallow cpu events for unpriv
  2 - Disallow kernel profiling for unpriv



thanks,
jirka


---
diff --git a/tools/lib/api/fs/tracing_path.c b/tools/lib/api/fs/tracing_path.c
index 38aca2dd1946..0406a7d5c891 100644
--- a/tools/lib/api/fs/tracing_path.c
+++ b/tools/lib/api/fs/tracing_path.c
@@ -12,12 +12,14 @@
 #include "tracing_path.h"
 
 
+char tracing_mnt[PATH_MAX + 1]         = "/sys/kernel/debug";
 char tracing_path[PATH_MAX + 1]        = "/sys/kernel/debug/tracing";
 char tracing_events_path[PATH_MAX + 1] = "/sys/kernel/debug/tracing/events";
 
 
 static void __tracing_path_set(const char *tracing, const char *mountpoint)
 {
+	snprintf(tracing_mnt, sizeof(tracing_mnt), "%s", mountpoint);
 	snprintf(tracing_path, sizeof(tracing_path), "%s/%s",
 		 mountpoint, tracing);
 	snprintf(tracing_events_path, sizeof(tracing_events_path), "%s/%s%s",
@@ -109,19 +111,10 @@ static int strerror_open(int err, char *buf, size_t size, const char *filename)
 			 "Hint:\tTry 'sudo mount -t debugfs nodev /sys/kernel/debug'");
 		break;
 	case EACCES: {
-		const char *mountpoint = debugfs__mountpoint();
-
-		if (!access(mountpoint, R_OK) && strncmp(filename, "tracing/", 8) == 0) {
-			const char *tracefs_mntpoint = tracefs__mountpoint();
-
-			if (tracefs_mntpoint)
-				mountpoint = tracefs__mountpoint();
-		}
-
 		snprintf(buf, size,
 			 "Error:\tNo permissions to read %s/%s\n"
 			 "Hint:\tTry 'sudo mount -o remount,mode=755 %s'\n",
-			 tracing_events_path, filename, mountpoint);
+			 tracing_events_path, filename, tracing_mnt);
 	}
 		break;
 	default: