netdev - Re: [PATCH v4 06/10] e1000e: Support for byte queue limits

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Date:	Thu, 01 Dec 2011 17:40:09 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 06/10] e1000e: Support for byte queue limits

Le jeudi 01 décembre 2011 à 08:32 -0800, Tom Herbert a écrit :
> > OK, as stated on your other thread, its obvious this driver (and
> > probably other intel drivers) made assumptions that are now obsolete,
> > since skb head can contain some data payload, not only (MAC+IP+TCP)
> > headers.
> >
> Looks like similar is in several Intel drivers.  Only other driver I
> found that is using the false assumption is tg3 IPv6 gso path.
> 
> > If Intel guys cannot afford approximate the bytecount by skb->len, I
> > suggest to use same trick found in
> > drivers/net/ethernet/intel/igb/igb_main.c
> >
> > static int igb_tso(struct igb_ring *tx_ring,
> > ...
> >        /* compute header lengths */
> >        l4len = tcp_hdrlen(skb);
> >        *hdr_len = skb_transport_offset(skb) + l4len;
> >
> I noticed a similar technique used by several drivers.  it's fine if
> it already knew the packet was TCP.  Just assuming that a GSO packet
> is TCP might be a new bug, so in the e1000e driver they would need to
> check the type (gso_type == SKB_GSO_TCPV4 or SKB_GSO_TCPV6).
> 
> I'm not sure that tcp_hdrlen is even being used correctly in the other
> drivers.  For instance in bnx2x, tcp_hdrlen is called after checking
> skb_is_gso_v6(skb) and skb_is_gso(skb).  If the former is true then in
> fact it is a TCP packet (gso_type is SKB_GSO_TCPV6) , but the if the
> latter is true it only proves that is is GSO packet (gso_type not
> checked, only gso_size>0)--  the packet might be a fragment UDP packet
> for instance, so tcphdr_len is not valid on those skbs.

To my knowledge, only one NIC (neterion/s2io) supports NETIF_F_UFO.

So all others only receive tcp gso frames.



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