perf trace: Use vfs_getname hook if available

Initially it tries to find a probe:vfs_getname that should be setup
with:

 perf probe 'vfs_getname=getname_flags:65 pathname=result->name:string'

or with slight changes to cope with code flux in the getname_flags code.

In the future, if a "vfs:getname" tracepoint becomes available, then it
will be preferred.

This is not strictly required and more expensive method of reading the
/proc/pid/fd/ symlink will be used when the fd->path array entry is not
populated by a previous vfs_getname + open syscall ret sequence.

As with any other 'perf probe' probe the setup must be done just once
and the probe will be left inactive, waiting for users, be it 'perf
trace' of any other tool.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-ujg8se8glq5izmu8cdkq15po@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/tools/perf/Documentation/perf-trace.txt b/tools/perf/Documentation/perf-trace.txt
index 54139c6..7b0497f 100644
--- a/tools/perf/Documentation/perf-trace.txt
+++ b/tools/perf/Documentation/perf-trace.txt
@@ -97,6 +97,10 @@ the thread executes on the designated CPUs. Default is to monitor all CPUs.
 	Show a summary of syscalls by thread with min, max, and average times (in
     msec) and relative stddev.
 
+--tool_stats::
+	Show tool stats such as number of times fd->pathname was discovered thru
+	hooking the open syscall return + vfs_getname or via reading /proc/pid/fd, etc.
+
 SEE ALSO
 --------
 linkperf:perf-record[1], linkperf:perf-script[1]