linux-kernel - Re: Rationale for paccept() sigset argument?

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Message-ID: <cfd18e0f0808291345t5b66fa3dyb48de41095f8425f@mail.gmail.com>
Date:	Fri, 29 Aug 2008 22:45:40 +0200
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Ulrich Drepper" <drepper@...hat.com>
Cc:	"Davide Libenzi" <davidel@...ilserver.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Jakub Jelinek" <jakub@...hat.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: Re: Rationale for paccept() sigset argument?

Ulrich -- Ping!

On Wed, Aug 20, 2008 at 6:50 PM, Michael Kerrisk
<mtk.manpages@...glemail.com> wrote:
> Ulrich,
>
> I'll need to cover this point in the man pages, and the rationale still
> isn't
> clear to me, so I'll check it with you...
>
> 2.6.27-rc has paccept():
>
> int paccept(int fd, struct sockaddr *sockaddr, socklen_t *addrlen,
>        const sigset_t *sigmask, int setsize, int flags)
>
> paccept() blocks until either a connection is received on fd, or a signal is
> sigmask() is caught.
>
> What is the rationale for the sigset argument of paccept()?
>
> For pselect()/ppoll()/epoll_pwait(), the sigset argument allows us to deal
> with a not uncommon situation: waiting for both signals and (multiple) file
> descriptors.  (The alternative is the self-pipe trick, which requires more
> programming effort.)
>
> However, do we really need this argument for paccept()?  I ask this for the
> following reasons:
>
> * This seems to be special casing for accept().  But there are other system
> calls (e.g., open(), connect(), recvfrom()) that are similar, in the sense
> that they may wait on a file descriptor, for which there is no [perceived
> need for a] sigset argument.
>
> * It seems to me that any case where we might want to use paccept() could be
> equivalently dealt with using the existing pselect()/ppoll()/epoll_pwait()
> followed by a conventional accept() if the listening file descriptor
> indicates as ready.  (But perhaps I missed something?)
>
> Can you please explain why we need this special case for [p]accept()?
>
> Cheers,
>
> Michael
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
> Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
>
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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