Re: [PATCH] perf test shell: Fix check open filename arg using 'perf trace'

[Michael Petlan <mpetlan@redhat.com>]

On Fri, 1 Dec 2017, Arnaldo Carvalho de Melo wrote:
> Em Fri, Dec 01, 2017 at 11:33:14AM +0900, Namhyung Kim escreveu:
[...]
>  
> > > What differs from x86 to others is that x86 uses syscalltbl, not requiring
> > > audit-libs to map syscall numbers to names, so perhaps it is something in there...
>  
> > If it only needs to consider open or openat, why not specifying the
> > both directly?
>  
> >   # perf trace -e open -e openat touch /etc/passwd
> 
> Same effect, works with other perf trace versions, but one suggestion to
> make it shorter:
> 
> 	perf trace -e open,openat touch /etc/passwd
> 
> Does the same thing :-)

Well, do I understand it correctly, that we prefer the "-e open,openat" over
the "-e 'open*'" because there are issues with the globbing feature on some
architectures?

I see a disadvantage of "-e open,openat" concept in that it does not work
in case any of them is unavailable. So in case some kernel does not contain
e.g. open in favor of openat, perf-trace fails to trace them. This can be
easily simulated like `perf trace -e open,openit`:

event syntax error: 'openit'
                     \___ Cannot find PMU `openit'. Missing kernel support?
Run 'perf list' for a list of valid events

Since it is possible that open is not even supported, having both of them
there is fragile. The "-e 'open*'" approach should expand only to supported
syscalls.

The '' are necessary there, since just open* can expand to some filename.

.....

I also see problems with globbing on my aarch64 with 4.14, so that makes
the "-e 'open*'" fragile too...

Ideas?

> 
> Michael, can you please take that into account and resubmit the patch?
> 
> - Arnaldo
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