Em Mon, Jan 06, 2014 at 10:01:35PM +0100, Yann Droneaud escreveu:
> Hi,
>
> Le lundi 06 janvier 2014 à 11:43 -0300, Arnaldo Carvalho de Melo a
> écrit :
> > Em Mon, Jan 06, 2014 at 12:24:36PM +0100, Peter Zijlstra escreveu:
>
> > > acme, ACK? I was thinking I'd keep these two patches together so the
> > > entire things lands in tip in one go?
> >
> > Nope, it should notice the EINVAL, drop the flag that doesn't work on
> > older kernels, retry, so that new tools continue to work on older
> > kernels, with yet another fallback.
> >
>
> But it may be difficult to distinguish the 'origin' of EINVAL: is it
> from FD_CLOEXEC flag or from an unsupported parameter in the attributes.
It definitely is, that is why the first thing to fall back is the most
recently added feature.
> > Please take a look at __perf_evsel__open(), probably it will be best to
> > add a flag to perf_missing_features, like the one we have for the
> > perf_event_attr.mmap2 flag, so that we fail just once, etc.
> >
>
> Unfortunately perf_event_open() is called in multiple places, not only
> in __perf_evsel__open(). So a more generic solution should be designed.
>
> Is something like the function proposed in message
> <1389022310.13828.9.camel@localhost.localdomain> [1]
> ok to be added to its own module:
Well, at least make it set a perf_missing_features flag instead of that
'cloexec' global, that way the routines that use perf_evsel__open would
reuse it.
- Arnaldo
> static int cloexec = PERF_FLAG_FD_CLOEXEC;
>
> int perf_flag_fd_cloexec(void)
> {
> static int probed;
>
> if (!probed) {
> struct perf_event_attr attr = { 0 };
> int fd = perf_event_open(&attr, 0, -1, -1,
> PERF_FLAG_FD_CLOEXEC);
> probed = 1;
> if (fd >= 0)
> close(fd);
> else
> cloexec = 0;
> }
>
> return cloexec;
> }
>
> This function should be used to build the flag passed to
> perf_event_open().
>
> Regards.
>
> [1]
> http://lkml.kernel.org/r/1389022310.13828.9.camel@localhost.localdomain
>
> --
> Yann Droneaud
> OPTEYA
>
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