linux-kernel - Re: F_DUPFD_CLOEXEC implementation

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Message-ID: <47014224.4030204@msgid.tls.msk.ru>
Date:	Mon, 01 Oct 2007 22:53:24 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	Al Viro <viro@....linux.org.uk>
CC:	Denys Vlasenko <vda.linux@...glemail.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Ulrich Drepper <drepper@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: F_DUPFD_CLOEXEC implementation

Al Viro wrote:
> On Mon, Oct 01, 2007 at 11:07:15AM +0100, Denys Vlasenko wrote:
>> Also attached is ndelaytest.c which can be used to test that
>> send(MSG_DONTWAIT) indeed is failing with EAGAIN if write would block
>> and that other processes never see O_NONBLOCK set.
>>
>> Comments?
> 
> Never send patches during or approaching hangover?
> 	* it's on a bunch of cyclic lists.  Have its neighbor
> go away while you are doing all that crap => boom
> 	* there's that thing call current position...  It gets buggered.
> 	* overwriting it while another task might be in the middle of
> syscall involving it => boom
> 	* non-cooperative tasks reading *in* *parallel* from the same
> opened file are going to have a lot more serious problems than agreeing
> on O_NONBLOCK anyway, so I really don't understand what the hell is that for.

Good summary... ;)

But for the last part of the last item - sometimes, definitely more than
once, I wondered why there's no equivalent to recv(MSG_DONTWAIT) for
non-sockets -- why for sockets it's as simple as adding an option (a
single bit), while for all the rest it requires two fcntl calls...
Sometimes it's handy. ;)

Not that I'm arguing for or against such a feature anyway..

/mjt
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