netdev - Re: recvmmsg() timeout behavior strangeness

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Message-ID: <50EEDD3F.9080203@genband.com>
Date:	Thu, 10 Jan 2013 09:24:47 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	Steven Whitehouse <steve@...gwyn.com>
CC:	Michael Kerrisk <mtk.manpages@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Caitlin Bestler <caitlin.bestler@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Chris Van Hoof <vanhoof@...hat.com>,
	Clark Williams <williams@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andrew Grover <andy.grover@...il.com>,
	Elie De Brauwer <eliedebrauwer@...il.com>,
	linux-man@...r.kernel.org,
	Rémi Denis-Courmont 
	<remi.denis-courmont@...ia.com>
Subject: Re: recvmmsg() timeout behavior strangeness

On 01/10/2013 04:04 AM, Steven Whitehouse wrote:

> Which timeout are we talking about? I've been copied into the thread
> without seeing the start of it.

The discussion is about the timeout parameter for the recvmmsg() call. 
Currently in the recvmmsg() code it only checks the timeout after 
__sys_recvmsg() returns, so if __sys_recvmsg() blocks forever we could 
end up essentially ignoring the timeout.

> If this is the rcvtimeo then afaik this is supposed to be the max time
> that the call waits for data, but is overridden by MSG_DONTWAIT, for
> example, on a per call basis. I'd assume that recvmmsg should work
> exactly like recvmsg in this case unless there is a good reason for it
> to differ,

recvmsg() doesn't have a timeout parameter, so it uses SO_RCVTIMEO.

recvmmsg() has an explicit timeout parameter but it doesn't look like it 
works properly and the documentation doesn't mention how it is supposed 
to interact with SO_RCVTIMEO.

Chris
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