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Commit 7e2b10c1 authored by Tom Herbert's avatar Tom Herbert Committed by David S. Miller
Browse files

net: Support for multiple checksums with gso 



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: default avatarTom Herbert <therbert@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 77157e19

include/linux/skbuff.h

+25 −1
Original line number Diff line number Diff line
@@ -567,7 +567,8 @@ struct sk_buff { 
	 * headers if needed

	 */

	__u8			encapsulation:1;

	/* 6/8 bit hole (depending on ndisc_nodetype presence) */

	__u8			encap_hdr_csum:1;

	/* 5/7 bit hole (depending on ndisc_nodetype presence) */

	kmemcheck_bitfield_end(flags2);



#if defined CONFIG_NET_DMA || defined CONFIG_NET_RX_BUSY_POLL
@@ -2988,6 +2989,7 @@ static inline struct sec_path *skb_sec_path(struct sk_buff *skb) 
struct skb_gso_cb {

	int	mac_offset;

	int	encap_level;

	__u16	csum_start;

};

#define SKB_GSO_CB(skb) ((struct skb_gso_cb *)(skb)->cb)
@@ -3012,6 +3014,28 @@ static inline int gso_pskb_expand_head(struct sk_buff *skb, int extra) 
	return 0;

}



/* Compute the checksum for a gso segment. First compute the checksum value

 * from the start of transport header to SKB_GSO_CB(skb)->csum_start, and

 * then add in skb->csum (checksum from csum_start to end of packet).

 * skb->csum and csum_start are then updated to reflect the checksum of the

 * resultant packet starting from the transport header-- the resultant checksum

 * is in the res argument (i.e. normally zero or ~ of checksum of a pseudo

 * header.

 */

static inline __sum16 gso_make_checksum(struct sk_buff *skb, __wsum res)

{

	int plen = SKB_GSO_CB(skb)->csum_start - skb_headroom(skb) -

	    skb_transport_offset(skb);

	__u16 csum;



	csum = csum_fold(csum_partial(skb_transport_header(skb),

				      plen, skb->csum));

	skb->csum = res;

	SKB_GSO_CB(skb)->csum_start -= plen;



	return csum;

}



static inline bool skb_is_gso(const struct sk_buff *skb)

{

	return skb_shinfo(skb)->gso_size;

net/core/skbuff.c

+7 −1
Original line number Diff line number Diff line
@@ -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 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, 
			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);

net/ipv4/ip_tunnel_core.c

+8 −0
Original line number Diff line number Diff line
@@ -135,6 +135,14 @@ struct sk_buff *iptunnel_handle_offloads(struct sk_buff *skb, 
		return skb;

	}



	/* If packet is not gso and we are resolving any partial checksum,

	 * clear encapsulation flag. This allows setting CHECKSUM_PARTIAL

	 * on the outer header without confusing devices that implement

	 * NETIF_F_IP_CSUM with encapsulation.

	 */

	if (csum_help)

		skb->encapsulation = 0;



	if (skb->ip_summed == CHECKSUM_PARTIAL && csum_help) {

		err = skb_checksum_help(skb);

		if (unlikely(err))