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net: Support for multiple checksums with gso

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When creating a GSO packet segment we may need to set more than
one checksum in the packet (for instance a TCP checksum and
UDP checksum for VXLAN encapsulation). To be efficient, we want
to do checksum calculation for any part of the packet at most once.

This patch adds csum_start offset to skb_gso_cb. This tracks the
starting offset for skb->csum which is initially set in skb_segment.
When a protocol needs to compute a transport checksum it calls
gso_make_checksum which computes the checksum value from the start
of transport header to csum_start and then adds in skb->csum to get
the full checksum. skb->csum and csum_start are then updated to reflect
the checksum of the resultant packet starting from the transport header.

This patch also adds a flag to skbuff, encap_hdr_csum, which is set
in *gso_segment fucntions to indicate that a tunnel protocol needs
checksum calculation

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Herbert
2014-06-04 17:20:02 -07:00
committed by David S. Miller
parent 77157e1973
commit 7e2b10c1e5
3 changed files with 40 additions and 2 deletions
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8
net/core/skbuff.c
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@ -2885,7 +2885,9 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
if (unlikely(!proto))
return ERR_PTR(-EINVAL);
csum = !!can_checksum_protocol(features, proto);
csum = !head_skb->encap_hdr_csum &&
!!can_checksum_protocol(features, proto);
__skb_push(head_skb, doffset);
headroom = skb_headroom(head_skb);
pos = skb_headlen(head_skb);
@ -2983,6 +2985,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
nskb->csum = skb_copy_and_csum_bits(head_skb, offset,
skb_put(nskb, len),
len, 0);
SKB_GSO_CB(nskb)->csum_start =
skb_headroom(nskb) + offset;
continue;
}
@ -3052,6 +3056,8 @@ perform_csum_check:
nskb->csum = skb_checksum(nskb, doffset,
nskb->len - doffset, 0);
nskb->ip_summed = CHECKSUM_NONE;
SKB_GSO_CB(nskb)->csum_start =
skb_headroom(nskb) + doffset;
}
} while ((offset += len) < head_skb->len);