linux-kernel - Re: [PATCH] tools lib api fs: Store tracing mountpoint for better error message

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Date:	Sat, 19 Sep 2015 11:26:20 -0400
From:	Raphaël Beamonte <raphael.beamonte@...il.com>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] tools lib api fs: Store tracing mountpoint for better
 error message

2015-09-19 10:47 GMT-04:00 Jiri Olsa <jolsa@...nel.org>:
> Storing the actual tracing path mountpoint to display correct
> error message hint ('Hint:' line). The error hint rediscovers
> mountpoints, but it could be different from what we actually
> used in tracing path.
>
> Before we'd display debugfs mount even though tracefs was used:
>   $ 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/events/sched/sched_krava
>   Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'
>   ...
>
> After this change, correct mountpoint is displayed:
>   $ 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/events/sched/sched_krava
>   Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'
>   ...
>
> Link: http://lkml.kernel.org/n/tip-xw7mf64ie0svh6m449vbyh0m@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/lib/api/fs/tracing_path.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
>
> 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:
> --
> 2.4.3
>

Reviewed-by: Raphaël Beamonte <raphael.beamonte@...il.com>
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