netdev - Re: [PATCH] virtio_net: Fix MAX_PACKET

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Date:	Tue, 20 Jan 2009 16:59:26 +0000
From:	Mark McLoughlin <markmc@...hat.com>
To:	Alex Williamson <alex.williamson@...com>
Cc:	netdev@...r.kernel.org, rusty@...tcorp.com.au, kvm@...r.kernel.org
Subject: Re: [PATCH] virtio_net: Fix MAX_PACKET_LEN to support 802.1Q VLANs

On Tue, 2009-01-20 at 09:48 -0700, Alex Williamson wrote:

> 802.1Q expanded the maximum ethernet frame size by 4 bytes for the
> VLAN tag.  We're not taking this into account in virtio_net, which
> means the buffers we provide to the backend in the virtqueue RX ring
> aren't big enough to hold a full MTU VLAN packet.  For QEMU/KVM,
> this results in the backend exiting with a packet truncation error.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...com>

Acked-by: Mark McLoughlin <markmc@...hat.com>

Note 1: this only matters if the guest isn't using mergeable receive
buffers or GSO

Note 2: IMHO, this should go in 2.6.29 and stable

Cheers,
Mark.

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