Date: Sat, 10 Jan 2009 23:31:30 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Casey Dahlin <cdahlin@redhat.com>
Cc: Scott James Remnant <scott@canonical.com>, Ingo Molnar <mingo@elte.hu>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Randy Dunlap <randy.dunlap@oracle.com>,
       Roland McGrath <roland@redhat.com>,
       Davide Libenzi <davidel@xmailserver.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RESEND][RFC PATCH v2] waitfd
Message-ID: <20090110223130.GA28581@redhat.com>
References: <49639EB8.40204@redhat.com> <4963ABF0.6070400@redhat.com> <20090107123457.GB16268@elte.hu> <20090107171922.GA18000@redhat.com> <1231598863.11642.55.camel@quest> <49690FC9.4010403@redhat.com>
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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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