perf trace & vfs_getname

[Milian Wolff <milian.wolff@kdab.com>]

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Hey Arnaldo,

I just wanted to try out your ongoing work to get file names printed in perf 
trace:

~~~~~~~~~~~~~~
$ perf trace -e open ls builtin-trace.c
     0.007 ( 0.007 ms): ls/26364 open(filename: 0x2a1b0d20, flags: CLOEXEC                             
) = -1 ENOENT No such file or directorybuiltin-trace.c

     0.022 ( 0.002 ms): ls/26364 open(filename: 0x2a1b0d20, flags: CLOEXEC                             
) = -1 ENOENT No such file or directory
...
~~~~~~~~~~~~~~

So apparently I still have to manually create the probe for vfs_getname. Could 
this be simplified for the user? E.g. by adding a static tracepoint for that 
purpose, so one doesn't have to run `perf probe` manually? Also, note that 
`vfs_getname` is only mentioned in `man perf trace` for its `--tool_stats` 
parameter, but the actual line to create the probe is nowhere to be found. 

Grepping the git log I found the following invocation, which errors out on my 
Arch machine:

~~~~~~~~~~~~~~~
$ perf probe 'vfs_getname=getname_flags:72 pathname=filename:string'
The /home/milian/.debug/.build-id/1a/03b857e3611b7a14fbf60d67cad7415706a933 
file has no debug information.
Rebuild with CONFIG_DEBUG_INFO=y, or install an appropriate debuginfo package.
  Error: Failed to add events.
~~~~~~~~~~~~~~~

On a different Arch machine it's:

~~~~~~~~~~~~~~~
$ perf probe 'vfs_getname=getname_flags:72 pathname=filename:string'
The /lib/modules/4.5.4-1-ARCH/build/vmlinux file has no debug information.
Rebuild with CONFIG_DEBUG_INFO=y, or install an appropriate debuginfo package.
  Error: Failed to add events.
~~~~~~~~~~~~~~~

On an Ubuntu 16.04 I'm getting this:

~~~~~~~~~~~~~~~
$ perf probe 'vfs_getname=getname_flags:72 pathname=filename:string'
Failed to find the path for kernel: No such file or directory
  Error: Failed to add events.
~~~~~~~~~~~~~~~

So does this really mean I'm out of luck?
-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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