Re: paccept() oddity

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 20 Aug 2008 18:50:54 +0200 Michael Kerrisk <mtk.manpages@googlemail.com> wrote:

> Ulrich,
> 
> [
> 2.6.27-rc has paccept():
> 
> int paccept(int fd, struct sockaddr *sockaddr, socklen_t *addrlen,
>          const sigset_t *sigmask, int setsize, int flags)
> ]
> 
> While considering the sigset argument for paccept() (see my previous
> message), and testing that system call, I realized that there is a certain
> oddness in the implementation of paccept().
> 
> Like accept(), paccept() automatically restarts if interrupted by a signal
> handler that was established with the SA_RESTART flag.
> 
> On the other hand, pselect(), ppoll(), and epoll_pwait() are never restarted
> if interrupted by a handler, even if the handler was established with
> SA_RESTART.  (This is the same as with select(), poll(), and epoll_wait().)
> 
> It seems to me that it makes little sense to restart paccept(), especially in
> the case where it is interrupted by a handler for one of the signals that is
> in sigmask, since the whole point of calling paccept() is to block until a
> connection is received, or until one of the signals in sigmask is caught().
> 
> How about changing paccept() so that it is never automatically restarted if
> interrupted by a signal handler, regardless of the SA_RESTART flag.  (In
> other words, paccept() should be consistent with pselect(), ppoll(), and
> epoll_pwait(), rather than being consistent with accept().)  What are your
> thoughts?
> 

Oleg, Roland: would you have the time to ponder the above, please?

If we can't get this nailed down very soon I'd suggest that we disable
sys_paccept() for 2.6.27.  We don't want to be releasing a new system
call into 2.6.27 if there are doubts surrounding its userspace-visible
behaviour.

Thanks.