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

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Date:	Sat, 12 Sep 2015 01:09:31 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Raphaël Beamonte <raphael.beamonte@...il.com>
Subject: Re: [PATCH 5/5] perf tools: Enhance parsing events tracepoint error
 output

Hi Jiri,

On Thu, Sep 10, 2015 at 10:05:37AM +0200, Jiri Olsa wrote:
> 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?

Sure, this patch displays the proper tracefs mountpoint.  But it also
has a problem - if tracefs is mounted under debugfs, the access mode
of debugfs also affects, so in this case I had to change it both for
debugfs and tracefs..


> 
> > 
> > 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:

Ah, great. :)

Thanks,
Namhyung


> [jolsa@...va 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@...va perf]$ sudo mount -o remount,mode=755 /sys/kernel/debug/tracing
> [jolsa@...va 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:
--
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