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Message-ID: <48AC4B6E.4040409@gmail.com>
Date: Wed, 20 Aug 2008 18:50:54 +0200
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To: Ulrich Drepper <drepper@redhat.com>
CC: Davide Libenzi <davidel@xmailserver.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       lkml <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: paccept() oddity
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From: Michael Kerrisk <mtk.manpages@googlemail.com>
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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?

Cheers,

Michael