linux-kernel - Re: [RESEND][RFC PATCH v2] waitfd

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Message-ID: <20090110223130.GA28581@redhat.com>
Date:	Sat, 10 Jan 2009 23:31:30 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Casey Dahlin <cdahlin@...hat.com>
Cc:	Scott James Remnant <scott@...onical.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Roland McGrath <roland@...hat.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RESEND][RFC PATCH v2] waitfd

On 01/10, Casey Dahlin wrote:
>
> Scott James Remnant wrote:
>> On Wed, 2009-01-07 at 18:19 +0100, Oleg Nesterov wrote:
>>
>>> Please note that unlike other sys_...fd() syscalls, sys_waitfd()
>>> doesn't allow to pass O_CLOEXEC. Looks like we need a separate
>>> "flags" argument...
>>>
>>> Also, ioctl(FIONBIO) or fcntl(O_NONBLOCK) have no effect on
>>> waitfd, not very good.
>>>
>>> I'd suggest to remove WNOHANG from waitfd_ctx->ops and treat
>>> (->f_flags & O_NONBLOCK) as WNOHANG.
>>>
>>> (can't resist, ->ops is not the best name ;)
>>>
>>>
>> Definitely agree here, waitfd() doesn't need WNOHANG - we already have
>> ONONBLOCK.
>>
>> That also solves one of the strangest behaves of waitid when you use
>> WNOHANG (it returns zero and you have to check whether it changed the
>> struct), now you just read() - if no child you get EAGAIN, if a child
>> you read a struct.
>>
> From the perspective of waitfd, the only difference between WNOHANG and
> O_NONBLOCK is which argument you put the flags in.

No. Please see the note about ioctl/fcntl above.

Oleg.

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