From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Westphal Subject: Re: recvmmsg() timeout behavior strangeness [RESEND] Date: Sat, 3 May 2014 13:29:05 +0200 Message-ID: <20140503112905.GC3514@breakpoint.cc> References: <536101C9.9090601@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Michael Kerrisk (man-pages)" Cc: Arnaldo Carvalho de Melo , lkml , "linux-man@vger.kernel.org" , netdev , =?utf-8?B?T25kxZllaiBCw61sa2E=?= , Caitlin Bestler , Neil Horman , Elie De Brauwer , David Miller , Steven Whitehouse , =?iso-8859-15?Q?R=E9mi?= Denis-Courmont , Paul Moore , Chris Friesen List-Id: linux-man@vger.kernel.org Michael Kerrisk (man-pages) 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?