sigwait return 4

[Kostik Belousov]

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.

So I think that we have a bug in the man page.

diff --git a/lib/libc/sys/sigwait.2 b/lib/libc/sys/sigwait.2
index 8c00cf4..b462201 100644
--- a/lib/libc/sys/sigwait.2
+++ b/lib/libc/sys/sigwait.2
@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 11, 2005
+.Dd August 24, 2011
 .Dt SIGWAIT 2
 .Os
 .Sh NAME
@@ -94,6 +94,8 @@ The
 .Fn sigwait
 system call will fail if:
 .Bl -tag -width Er
+.It Bq Er EINTR
+The system call was interrupted by an unblocked, caught signal.
 .It Bq Er EINVAL
 The
 .Fa set
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