netdev - Re: [PATCH] datagram: Extend the datagram queue MSG

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Message-ID: <1328884902.2443.29.camel@edumazet-laptop>
Date:	Fri, 10 Feb 2012 15:41:42 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	David Miller <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH] datagram: Extend the datagram queue MSG_PEEK-ing

Le vendredi 10 février 2012 à 17:54 +0400, Pavel Emelyanov a écrit :
> We're working on the checkpoint-restore project. To checkpoint a unix socket
> we need to read its skb queue. Analogous task for TCP sockets Tejun proposed
> to solve with parasite + recvmsg + MSG_PEEK. That's nice, but doesn't work
> for unix sockets, because for them MSG_PEEK always peeks a single skb from the 
> head of the queue.
> 
> I propose to extend the MSG_PEEK functionality with two more flags that peek
> either next not picked skb in queue or pick the last picked one. The latter
> ability is required to make it possible to re-read a message if MSG_TRUNC
> was reported on it.
> 
> These two flags can be used for unix stream sockets, since making the MSG_PEEK
> just report all data that fits the buffer length is bad -- we may have scms
> in queue thus turning stream socket into dgram one.
> 
> Signed-off-by: Pavel Emelyanov <xemul@...allels.com>
> 
> ---

Nice !

So this CR stuff assumes an application wont use itself MSG_PEEK /
MORE / AGAIN ?

(skb->peeked can only be set, never unset)



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