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

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Message-ID: <cfd18e0f0809080633k3989f514k69dae13063db137b@mail.gmail.com>
Date:	Mon, 8 Sep 2008 15:33:46 +0200
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Ulrich Drepper" <drepper@...hat.com>
Cc:	"Michael Kerrisk" <mtk.manpages@...glemail.com>,
	"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!

---------- Forwarded message ----------
From: Michael Kerrisk <mtk.manpages@...glemail.com>
Date: Sep 2, 2008 9:58 AM
Subject: Re: Rationale for paccept() sigset argument?
To: Ulrich Drepper <drepper@...il.com>
Cc: Michael Kerrisk <mtk.manpages@...glemail.com>, Ulrich Drepper
<drepper@...hat.com>, 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>


Ulrich Drepper wrote:
> On Wed, Aug 20, 2008 at 9:50 AM, Michael Kerrisk
> <mtk.manpages@...glemail.com> wrote:
>
> > What is the rationale for the sigset argument of paccept()?
> >
>
> accept, like select/poll, is used often as a function to dealy
> operation.  Unlike read, recv, etc, which are handled using O_NONBLOCK
> and select/poll.  pselect/ppoll do not really have a sigset parameter
> to handle signals in general.  You use it to enable special handling
> in case of blocking.  Example: if you want to implement userlevel
> context switching, you dedicate a signal to wake up any blocked
> thread.  Since accept falls more into the same category than poll,
> this means the sigset parameter is justified.  In theory we could add
> it to all functions but there is no reason to do this without any
> other reason to change the interface.
>


Ulrich, you snipped a relevant piece of my earlier message:

[[
> * 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.
]]

So I'll rephrase: what use case does the sigset argument of paccept()
allow us to handle that couldn't equally have been handled by
pselect()/ppoll()/epoll_pwait() + traditional accept()?


Cheers,

Michael
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