netdev - RE: [PATCH] net: unix: non blocking recvmsg() should not return -EINTR

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6EA7FB@AcuExch.aculab.com>
Date:	Thu, 27 Mar 2014 12:53:58 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Rainer Weikusat' <rweikusat@...ileactivedefense.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH] net: unix: non blocking recvmsg() should not return
 -EINTR

From: Rainer Weikusat 
> Considering all of this, the trylock-approach seems best to me. OTOH,

No - using trylock() is definitely wrong.
If there are two messages queued and two processes/threads try to
read them, you don't want one of them being given EAGAIN.

If we ignore the case where there are some blocking and some
non-blocking readers (which doesn't work for other reasons)
then it would actually make sense for the non-blocking
code to wait uninterruptibly (possibly with a timeout that
should never expire) and for the blocking code to wait
interruptibly (as currently).

Then problem of which error code to return is moot.

	David

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