Re: [PATCH/RFC] net: Don't save mid batch datagram processing error for next recvmmsg call

[David Miller <davem@davemloft.net>]

From: Arnaldo Carvalho de Melo <acme@kernel.org>
Date: Mon, 21 Jul 2014 16:30:42 -0300

> From 5cf1a5c682c8bb0add9adfb5167a63f269136523 Mon Sep 17 00:00:00 2001
> From: Arnaldo Carvalho de Melo <acme@redhat.com>
> Date: Mon, 21 Jul 2014 12:39:56 -0300
> Subject: [PATCH 2/2] net: Don't save mid batch datagram processing error for
>  next recvmmsg call
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> When the call to the underlying per protocol recvmsg fails for some
> reason and we already have successfully processed at least one datagram
> in the batch, we were saving the error for the next recvmmsg (or
> recvmsg) call, so the user would eventually get notified of what
> happened.
> 
> This was found to be fraught with problems, as, for instance, errors
> could be notified for a different thread than a faulty one providing
> invalid buffers.
> 
> So just return the number of datagrams successfully received.
> 
> Reported-by: David Laight <David.Laight@ACULAB.COM>
 ...
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

This is absolutely correct, any time we have a partial success we must
indicate success and the amount that was properly transferred, leaving
the error signalling for a subsequent retry (if any).