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Date:	Wed, 21 May 2014 18:05:35 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Ondřej Bílka <neleai@...nam.cz>,
	Caitlin Bestler <caitlin.bestler@...il.com>,
	Neil Horman <nhorman@...driver.com>,
	Elie De Brauwer <eliedebrauwer@...il.com>,
	David Miller <davem@...emloft.net>,
	Steven Whitehouse <steve@...gwyn.com>,
	Rémi Denis-Courmont 
	<remi.denis-courmont@...ia.com>, Paul Moore <paul@...l-moore.com>,
	Chris Friesen <chris.friesen@...driver.com>
Subject: [PATCH/RFC] Re: recvmmsg() timeout behavior strangeness [RESEND]

Em Mon, May 12, 2014 at 11:34:51AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, May 12, 2014 at 12:15:25PM +0200, Michael Kerrisk (man-pages) escreveu:
> > Hi Arnaldo,
 
> > Ping!

> I acknowledge the problem, the timeout has to be passed to the
> underlying ->recvmsg() implementations that should return the time spent
> waiting for each packet, so that we can accrue that at recvmmsg level.
 
> We can do either passing an extra timeout parameter to the recvmsg
> implementations or using some struct sock member to specify that
> timeout.
 
> The first approach is intrusive, touches tons of files, so I'll try
> making it all mostly transparent by hooking into sock_rcvtimeo()
> somehow.

But after thinking a bit more, looks like we need to do that, please
take a look at the attached patch to see if it addresses the problem.

Mostly it adds a new timeop to the per protocol recvmsg()
implementations, that, if not NULL, should be used instead of
SO_RCVTIMEO.

since the underlying recvmsg implementations already check that timeout,
return what is remaining, that will then be used in subsequent recvmsg
calls, at the end we just convert it back to timespec format.

In most cases it is just passed to skb_recv_datagram, that will check
the pointer, use it and update if not NULL.

Should have no problems, but I only did a boot with a system with this
patch applied, no problems noticed on a normal desktop session, ssh,
etc.

 Arnaldo

View attachment "recvmmsg-timeout.patch" of type "text/plain" (72597 bytes)

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