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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next] af_unix: MSG_TRUNC support for dgram sockets
Date: Wed, 22 Feb 2012 14:50:28 -0500 (EST)
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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 22 Feb 2012 10:24:55 +0100

> Piergiorgio Beruto expressed the need to fetch size of first datagram in
> queue for AF_UNIX sockets and suggested a patch against SIOCINQ ioctl.
> 
> I suggested instead to implement MSG_TRUNC support as a recv() input
> flag, as already done for RAW, UDP & NETLINK sockets.
> 
> len = recv(fd, &byte, 1, MSG_PEEK | MSG_TRUNC);
> 
> MSG_TRUNC asks recv() to return the real length of the packet, even when
> is was longer than the passed buffer.
> 
> There is risk that a userland application used MSG_TRUNC by accident
> (since it had no effect on af_unix sockets) and this might break after
> this patch.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Tested-by: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
> CC: Michael Kerrisk <mtk.manpages@gmail.com>

Applied.