sigwait() cancellation point

[Kostik Belousov]

On Tue, Sep 07, 2010 at 05:38:06PM +0000, David Xu wrote:
> Jilles Tjoelker wrote:
> >Our sigwait() implementation may not be POSIX-compliant as it returns
> >EINTR when it is interrupted by a caught signal. (Unfortunately I can
> >only find this in SUSv4 in the Rationale, B.2.3 Error Numbers,
> >Disallowing Return of the [EINTR] Error Code; the sigwait() page in XSH
> >does not list an [EINTR] error condition, but does not prohibit one
> >either like pthread_mutex_lock() and various others do.)
> >
> >However, libthr's wrapper for sigwait() relies on EINTR. To keep
> >the possibility of changing this to be what POSIX intends, it would be
> >nice to remove this dependency.
> >
> >One way is to include SIGCANCEL in the set of waited signals, but this
> >requires two additional syscalls to mask/unmask SIGCANCEL.
> >
> >Another way is to use sigwaitinfo() in the wrapper, which is permitted
> >to return [EINTR]. If [EINTR] is removed from the kernel sigwait(),
> >looping on [EINTR] can then be implemented in the wrapper.
> >
> >Calling pthread_exit from the SIGCANCEL handler is not possible as this
> >leaves the program in doubt about any signal consumed by sigwait().
> >
> I have worked out a patch:
> 
> http://people.freebsd.org/~davidxu/patch/sigwait.diff
Isn't __sys_sigwait() supposed to return -1 and set errno ?
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