linux-kernel - Re: paccept() oddity

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Message-Id: <20080911003833.265E7154210@magilla.localdomain>
Date:	Wed, 10 Sep 2008 17:38:33 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: paccept() oddity

I don't see any rationale for changing paccept to be an oddball special
case in its EINTR behavior.

select/poll are special cases historically, and that's why the principle of
least astonishment makes it best for pselect/ppoll to match their behavior.

The same principle makes it highly dubious to have paccept differ from
accept in such a subtlety.  I don't see any reason to want it, anyway.
An application that wants to see EINTR can just use sigaction to clear
SA_RESTART.

Frankly, I don't see the rationale for rolling the implicit sigprocmask
into paccept at all.  accept is analogous to read or other i/o calls,
not to select/poll.  It's not any normal plan to fiddle blocked signals
around a blocking i/o call.  Instead, programs use (p)select/poll (and
sometimes also O_NONBLOCK) to manage the blocking and waking up.  Then
when the program finally calls accept, it knows it won't block.  The
atomic signal machinery makes sense for pselect/ppoll to help manage the
corner cases of blocking/wakeup in event loops.  It makes no more sense
to roll blocked signal set changes into accept than it would to have
read, write, etc. all take a sigset_t and do that.

Thanks,
Roland
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