netdev - Re: [PATCH] af_packet: add interframe drop cmsg (v5)

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Message-ID: <4AC3D9FB.3050305@gmail.com>
Date:	Thu, 01 Oct 2009 00:21:47 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] af_packet: add interframe drop cmsg (v5)

Neil Horman a écrit :
> Gah, you're right, I'm sorry.  Version 5 attached
> 
> Change Notes:
> 
> 1) Fix record_packet_gap so that only the warning message is rate limited, not
> the actual capping of the gap value
> 
> ==========================================================
> 
> 
> Add Ancilliary data to better represent loss information
> 
> I've had a few requests recently to provide more detail regarding frame loss
> during an AF_PACKET packet capture session.  Specifically the requestors want to
> see where in a packet sequence frames were lost, i.e. they want to see that 40
> frames were lost between frames 302 and 303 in a packet capture file.  In order
> to do this we need:
> 
> 1) The kernel to export this data to user space
> 2) The applications to make use of it
> 
> This patch addresses item (1).  It does this by doing the following:
> 
> A) attaching ancilliary data to any skb enqueued to a socket recieve queue for
> which frames were lost between it and the previously enqueued frame.  Note I use
> a ring buffer with a correlator value (the skb pointer) to do this.  This was
> done because the skb->cb array is exhausted already for AF_PACKET
> 
> B) For any frame dequeued that has ancilliary data in the ring buffer (as
> determined by the correlator value), we add a cmsg structure to the msghdr that
> gets copied to user space, this cmsg structure is of cmsg_level AF_PACKET, and
> cmsg_type PACKET_GAPDATA.  It contains a u32 value which counts the number of
> frames lost between the reception of the frame being currently recevied and the
> frame most recently preceding it.  Note this creates a situation in which if we
> have packet loss followed immediately by a socket close operation we might miss
> some gap information.  This situation is covered by the use of the
> PACKET_AUXINFO socket option, which provides total loss stats (from which the
> final gap can be computed).
> 
> I've tested this patch myself, and it works well.
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> 

Thanks Neil

Acked-by: Eric Dumazet <eric.dumazet@...il.com>

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