From: "Michael Chan" <mchan@broadcom.com>
To: "Stephen Hemminger" <shemminger@vyatta.com>
Cc: "David Miller" <davem@davemloft.net>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: RFC - should network devices trim frames > soft mtu
Date: Wed, 31 Aug 2011 15:27:31 -0700 [thread overview]
Message-ID: <1314829651.9556.37.camel@HP1> (raw)
In-Reply-To: <20110831151823.23cfb7bc@nehalam.ftrdhcpuser.net>
On Wed, 2011-08-31 at 15:18 -0700, Stephen Hemminger wrote:
> I noticed the following in the bnx2 driver.
>
>
> static int
> bnx2_rx_int(struct bnx2 *bp, struct bnx2_napi *bnapi, int budget)
> {
> ...
> skb->protocol = eth_type_trans(skb, bp->dev);
>
> if ((len > (bp->dev->mtu + ETH_HLEN)) &&
> (ntohs(skb->protocol) != 0x8100)) {
>
> dev_kfree_skb(skb);
> goto next_rx;
>
> }
>
> This means that for non-VLAN tagged frames, the device drops received
> packets if the length is greater than the MTU. I don't see that in
> other devices. What is the correct method? IMHO the bnx2 driver is
> wrong here and if the policy is desired it should be enforced at
> the next level (netif_receive_skb). Hardcoding a protocol value is
> kind of a giveaway that something is fishy.
>
I guess the reasoning is that we program the RX MTU in our chip to
automatically discard packets bigger than the RX MTU and count them as
over-size packets. We add 4 bytes to the RX MTU to account for the VLAN
tag which may be stripped or not stripped by the chip depending on
settings. The extra 4 bytes in the RX MTU setting will allow over-size
packets by up to 4 bytes to get through.
I agree we should move this to the next level.
next prev parent reply other threads:[~2011-08-31 22:35 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-31 22:18 RFC - should network devices trim frames > soft mtu Stephen Hemminger
2011-08-31 22:26 ` Ben Greear
2011-08-31 22:27 ` Michael Chan [this message]
2011-09-01 0:10 ` David Lamparter
2011-08-31 22:45 ` Ben Hutchings
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