sigwait return 4

[Slawa Olhovchenkov]

On Wed, Aug 24, 2011 at 10:07:03PM +0300, Kostik Belousov wrote:

> On Wed, Aug 24, 2011 at 10:19:07PM +0400, Slawa Olhovchenkov wrote:
> > System is 8.2-RELEASE (GENERIC), amd64.
> > Application -- i386 for freebsd7.
> > 
> > In ktrace dump I find some strange result:
> > 
> >  22951 100556 kas-milter CALL  sigwait(0xffdfdf80,0xffdfdf7c)
> >  22951 100556 kas-milter RET   sigwait 4
> >  22951 100556 kas-milter PSIG  SIGUSR2 caught handler=0x804c0f0 mask=0x4003 code=0x0
> > 
> > RET   sigwait 4 confused me, and, I think, confused application too.
> > 
> > man sigwait:
> > 
> > ERRORS
> >      The sigwait() system call will fail if:
> > 
> >      [EINVAL]           The set argument specifies one or more invalid signal
> >                         numbers.
> > 
> >      [EFAULT]           Any arguments point outside the allocated address
> >                         space or there is a memory protection fault.
> > 
> > 
> > How sigwait can return '4'?
> > May be EINTR, converted from ERESTART? But kern_sigtimedwait from sigwait must 
> > be called with timeout == NULL...
> > 
> 
> What should the system do for a delivered signal not present in the set ?
> I guess this is the case of your ktrace.
> 
> Looking at the SUSv4, I see no mention of the situation, but in Oracle
> SunOS 5.10 man page for sigwait(2), it is said explicitely
> EINTR The wait was interrupted by an unblocked, caught signal.

I don't think you right in this case.
This is kas-milter and in this thread (this is multi-thread
application) kas-milter wait for USR2 for reload config.

System return from sigwait only on USR2, but not each return w/
non-zero return code.

On freebsd7 this application don't complain about sigwait's return value.