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virtio-net: put virtio net header inline with data

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For small packets we can simplify xmit processing
by linearizing buffers with the header:
most packets seem to have enough head room
we can use for this purpose.
Since existing hypervisors require that header
is the first s/g element, we need a feature bit
for this.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Michael S. Tsirkin 2013-07-25 10:20:23 +09:30 • committed by David S. Miller
parent 10eccb46b5
commit e7428e95a0
2 changed files with 37 additions and 9 deletions
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4
include/uapi/linux/virtio_net.h
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@ -70,7 +70,9 @@ struct virtio_net_config {
__u16 max_virtqueue_pairs;
} __attribute__((packed));
/* This is the first element of the scatter-gather list. If you don't
/* This header comes first in the scatter-gather list.
* If VIRTIO_F_ANY_LAYOUT is not negotiated, it must
* be the first element of the scatter-gather list. If you don't
* specify GSO or CSUM features, you can simply ignore the header. */
struct virtio_net_hdr {
#define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 // Use csum_start, csum_offset