netdev - Re: recvmmsg() timeout behavior strangeness [RESEND]

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Message-ID: <20140503112905.GC3514@breakpoint.cc>
Date:	Sat, 3 May 2014 13:29:05 +0200
From:	Florian Westphal <fw@...len.de>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	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: Re: recvmmsg() timeout behavior strangeness [RESEND]

Michael Kerrisk (man-pages) <mtk.manpages@...il.com> wrote:
> Reinvestigating the problem, I see that I got my description of the
> behavior slightly wrong, although the fundamental problem remains.
> Here's my improved formulation:
[..]

> Since the timeout is only checked after the arrival of each datagram,
> we can have scenarios like the following:
> 
> 0. Assume a timeout of 10 (T) seconds, that vlen is 5, and the call
>    is made at time X
> 
> 1. First datagram arrives at time X+2.
> 
> 2. Second datagram arrives at time X+4 secs
> 
> 3. Third datagram arrives at time X+6 secs
> 
> 4. No more datagrams arrive.
> 
> In this case, the call blocks forever. It hardly seems that this could
> be intended behavior. The problem, of course is that the timeout is
> checked only after receipt of a datagram.

Isn't that what MSG_WAITFORONE is supposed to solve?
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