Hi,
Le lundi 06 janvier 2014 à 15:22 +0100, Jiri Olsa a écrit :
> On Mon, Jan 06, 2014 at 11:51:25AM +0100, Yann Droneaud wrote:
> > In a previous patch [1][2], flag PERF_FLAG_FD_CLOEXEC was
> > added to perf_event_open(2) syscall to allows userspace
> > to enable close-on-exec behavor atomically when creating
> > the file descriptor.
> >
> > This patch makes perf tools use the new flag.
> >
> > Beware that perf tools compiled with the new flag won't work
> > on older kernel which do not support flag PERF_FLAG_FD_CLOEXEC.
>
> I think we should enhance the api probe routines (perf_do_probe_api)
> to detect that, than just bypass us from running on older kernels
>
perf_probe_api() is only available in tools/perf/util/record.c module
(eg. it's a static function), while I've modified all calls to
perf_event_open().
So if you want to follow the probe path, a new function should be added.
This function must be used to retrieve the value of the
PERF_FLAG_FD_CLOEXEC flag if available.
For example:
static int cloexec = PERF_FLAG_FD_CLOEXEC;
int perf_flag_fd_cloexec(void)
{
static int probed;
if (!probed) {
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;
}
But I don't know how to setup a struct perf_event_attr which will work
in "all" case (and do no harm).
I was able to run this code with attr struct cleared (eg. set to 0), but
I don't know perf internals enough to be confident.
Regards.
--
Yann Droneaud
OPTEYA
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