Re: [PATCH] perf tools: Fix tracing_path_mount proper path

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Tue, Oct 16, 2018 at 01:48:18PM +0200, Jiri Olsa escreveu:
> If there's no tracefs (RHEL7) support the tracing_path_mount
> returns debugfs path which results in following fail:
> 
>   # perf probe sys_write
>   kprobe_events file does not exist - please rebuild kernel with CONFIG_KPROBE_EVENTS.
>   Error: Failed to add events.
> 
> In tracing_path_debugfs_mount function we need to return the
> 'tracing' path instead of just the mount to make it work:
> 
>   # perf probe sys_write
>   Added new event:
>     probe:sys_write      (on sys_write)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe:sys_write -aR sleep 1
> 
> Adding the 'return tracing_path;' also to tracing_path_tracefs_mount
> function just for consistency with tracing_path_debugfs_mount.
> 
> Upstream keeps working, because it has the tracefs support.
> 
> Link: http://lkml.kernel.org/n/tip-yiwkzexq9fk1ey1xg3gnjlw4@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/lib/api/fs/tracing_path.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/api/fs/tracing_path.c b/tools/lib/api/fs/tracing_path.c
> index 120037496f77..5afb11b30fca 100644
> --- a/tools/lib/api/fs/tracing_path.c
> +++ b/tools/lib/api/fs/tracing_path.c
> @@ -36,7 +36,7 @@ static const char *tracing_path_tracefs_mount(void)
>  
>  	__tracing_path_set("", mnt);
>  
> -	return mnt;
> +	return tracing_path;
>  }
>  
>  static const char *tracing_path_debugfs_mount(void)
> @@ -49,7 +49,7 @@ static const char *tracing_path_debugfs_mount(void)
>  
>  	__tracing_path_set("tracing/", mnt);
>  
> -	return mnt;
> +	return tracing_path;

Humm, colour me confused, by the name of the function I expected
tracing_path_debugfs_mount() to return the debugfs mount.

tracing_path_tracefs_mount() would return the tracefs mount point, so,
there, returning tracing_path would be ok.

Is there some other way to figure out that tracefs isn't available and
thus we should use debugfs_mount + "/tracing/" for the "tracefs" mount?

This may well be just the naming confusion... lemme read this a bit
more...

- Arnaldo

>  }
>  
>  const char *tracing_path_mount(void)
> -- 
> 2.17.2