linux-kernel - Re: Problem with unix sockets: SOCK_DGRAM ignores MSG

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Date:	Wed, 7 Feb 2007 09:58:51 +0100
From:	Daniel Kabs <dkabs@...otix.com>
To:	davids@...master.com
Cc:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: Problem with unix sockets: SOCK_DGRAM ignores MSG_TRUNC

On Tuesday 06 February 2007 21:11, David Schwartz wrote:
> > Why not improve consistency and make unix_dgram_recvmsg() return the
> > full packet length? So it would behave as UDP does. What do you think
> > about adding the following code to linux/net/unix/af_unix.c:
>
> It would be nice if the world worked that way, but you can't break
> POSIX compliance. Perhaps another receive flag?

I now understand that setting the MSG_TRUNC flag is only applicable for 
PF_PACKET. I do not argue about that any more. :-)

What I question is the return value when receiving from a local socket 
using recv(). Sorry, I don't know what the POSIX standard has to say 
about receiving from local sockets in contrast to UDP sockets as my only 
reference are the man pages.

According to "man 2 recv", on success the return value is the "the  number  
of bytes received". Since patch-2.6.8, UDP is always returning the full 
packet length. I'd like to see local sockets (PF_UNIX) to do the same. 

Does POSIX stipulate a different behaviour for local sockets?

Cheers
Daniel
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