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

[Avi Kivity <avi@redhat.com>]

  On 10/08/2010 06:44 PM, Gleb Natapov wrote:
> On Thu, Oct 07, 2010 at 09:49:17PM -0300, Marcelo Tosatti wrote:
> >  On Thu, Oct 07, 2010 at 07:56:55PM +0200, Gleb Natapov wrote:
> >  >  >  >  diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >  >  >  >  index b8499f5..8800713 100644
> >  >  >  >  --- a/virt/kvm/kvm_main.c
> >  >  >  >  +++ b/virt/kvm/kvm_main.c
> >  >  >  >  @@ -1458,6 +1458,8 @@ static long kvm_vcpu_ioctl(struct file *filp,
> >  >  >  >   		if (arg)
> >  >  >  >   			goto out;
> >  >  >  >   		r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
> >  >  >  >  +		if (r>= 0)
> >  >  >  >  +			trace_kvm_userspace_exit(vcpu->run->exit_reason);
> >  >  >  >   		break;
> >  >  >  >   	case KVM_GET_REGS: {
> >  >  >  >   		struct kvm_regs *kvm_regs;
> >  >  >  >  --
> >  >  >  >  			Gleb.
> >  >  >
> >  >  >  Exit codes are also valid for r == -EINTR and -EAGAIN cases, eg
> >  >  >  EXIT_INTR. Better print it out for all cases, and let the reader
> >  >  >  decide whether exit_reason is valid.
> >  >  Are they? I see that userspace does not look into run->exit_reason in
> >  >  case of -EINTR and -EAGAIN.
> >
> >  Not userspace, but for a human reader. Otherwise the trace information
> >  is incomplete and confusing.
> But if we will always call trace_kvm_userspace_exit() here trace
> information will show erroneous info since on any error but -EINTR
> exit_reason contains stale info. What about changing r>= 0 to r>= 0 ||
> r ==  -EINTR.

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).

-- 
error compiling committee.c: too many arguments to function