Re: [PATCH] trace "exit to userspace" event

[Gleb Natapov <gleb@redhat.com>]

On Thu, Oct 14, 2010 at 01:11:20PM +0200, Avi Kivity wrote:
>  On 10/14/2010 12:29 PM, Gleb Natapov wrote:
> >On Thu, Oct 14, 2010 at 12:27:15PM +0200, Avi Kivity wrote:
> >>   On 10/10/2010 05:46 PM, Gleb Natapov wrote:
> >>  >>
> >>  >>   We should log both errno and exit_reason.  If we want to be clever,
> >>  >>   we can display strerror(errno) if it's nonzero, and exit_reason
> >>  >>   otherwise (easy to do in a trace-cmd plugin).
> >>  >>
> >>  >For starters we should remove KVM_EXIT_INTR exit reason. Looking into
> >>  >qemu-kvm history it was never used and there is at least one code path
> >>  >that returns -EINTR and does not set KVM_EXIT_INTR, so exit_reason field
> >>  >contains stale info on exit.
> >>  >
> >>
> >>  The two issues are unrelated.
> >>
> >So what do you propose? I see no issue with my original patch.
> 
> Record both errno and exit_reason.  While they're never both valid
> at the same time, they're both necessary.
> 
If they can't be valid at the same time, why not record one of them? The
one that happened? Also any error other then -EINTR will cause qemu to
stop, so it is not very interesting. And ioctl return value can be
traced by strace anyway.

--
			Gleb.