[NET]: Use csum_start offset instead of skb_transport_header

The skb transport pointer is currently used to specify the start
of the checksum region for transmit checksum offload.  Unfortunately,
the same pointer is also used during receive side processing.

This creates a problem when we want to retransmit a received
packet with partial checksums since the skb transport pointer
would be overwritten.

This patch solves this problem by creating a new 16-bit csum_start
offset value to replace the skb transport header for the purpose
of checksums.  This offset is calculated from skb->head so that
it does not have to change when skb->data changes.

No extra space is required since csum_offset itself fits within
a 16-bit word so we can use the other 16 bits for csum_start.

For backwards compatibility, just before we push a packet with
partial checksums off into the device driver, we set the skb
transport header to what it would have been under the old scheme.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9b2957d203c91dfb9ecaad4a3ffa3abd767c16b4..910560e855619917a5f7103bfbae9642f7ee139b 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -205,7 +205,9 @@ typedef unsigned char *sk_buff_data_t;
  *     @len: Length of actual data
  *     @data_len: Data length
  *     @mac_len: Length of link layer header
- *     @csum: Checksum
+ *     @csum: Checksum (must include start/offset pair)
+ *     @csum_start: Offset from skb->head where checksumming should start
+ *     @csum_offset: Offset from csum_start where checksum should be stored
  *     @local_df: allow local fragmentation
  *     @cloned: Head may be cloned (check refcnt to be sure)
  *     @nohdr: Payload reference only, must not modify header
@@ -261,7 +263,10 @@ struct sk_buff {
                                mac_len;
        union {
                __wsum          csum;
-               __u32           csum_offset;
+               struct {
+                       __u16   csum_start;
+                       __u16   csum_offset;
+               };
        };
        __u32                   priority;
        __u8                    local_df:1,

diff --git a/net/core/dev.c b/net/core/dev.c
index fec8cf27f75d2a7dc39fb316653eb62f84a45b31..d23972f56fc7828d7dd4fa8dfef0bee616edee5c 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1155,7 +1155,7 @@ EXPORT_SYMBOL(netif_device_attach);
 int skb_checksum_help(struct sk_buff *skb)
 {
        __wsum csum;
-       int ret = 0, offset = skb_transport_offset(skb);
+       int ret = 0, offset;
 
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                goto out_set_summed;
@@ -1171,15 +1171,16 @@ int skb_checksum_help(struct sk_buff *skb)
                        goto out;
        }
 
+       offset = skb->csum_start - skb_headroom(skb);
        BUG_ON(offset > (int)skb->len);
        csum = skb_checksum(skb, offset, skb->len-offset, 0);
 
-       offset = skb->tail - skb->transport_header;
+       offset = skb_headlen(skb) - offset;
        BUG_ON(offset <= 0);
        BUG_ON(skb->csum_offset + 2 > offset);
 
-       *(__sum16 *)(skb_transport_header(skb) +
-                    skb->csum_offset) = csum_fold(csum);
+       *(__sum16 *)(skb->head + skb->csum_start + skb->csum_offset) =
+               csum_fold(csum);
 out_set_summed:
        skb->ip_summed = CHECKSUM_NONE;
 out:
@@ -1431,12 +1432,16 @@ int dev_queue_xmit(struct sk_buff *skb)
        /* If packet is not checksummed and device does not support
         * checksumming for this protocol, complete checksumming here.
         */
-       if (skb->ip_summed == CHECKSUM_PARTIAL &&
-           (!(dev->features & NETIF_F_GEN_CSUM) &&
-            (!(dev->features & NETIF_F_IP_CSUM) ||
-             skb->protocol != htons(ETH_P_IP))))
-               if (skb_checksum_help(skb))
-                       goto out_kfree_skb;
+       if (skb->ip_summed == CHECKSUM_PARTIAL) {
+               skb_set_transport_header(skb, skb->csum_start -
+                                             skb_headroom(skb));
+
+               if (!(dev->features & NETIF_F_GEN_CSUM) &&
+                   (!(dev->features & NETIF_F_IP_CSUM) ||
+                    skb->protocol != htons(ETH_P_IP)))
+                       if (skb_checksum_help(skb))
+                               goto out_kfree_skb;
+       }
 
 gso:
        spin_lock_prefetch(&dev->queue_lock);

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4965df29768bb792b79a340969a4a6a45052933a..52a4fdd4f31c2cc5cb8ac012977b674d555256b5 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1358,7 +1358,7 @@ void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to)
        long csstart;
 
        if (skb->ip_summed == CHECKSUM_PARTIAL)
-               csstart = skb_transport_offset(skb);
+               csstart = skb->csum_start - skb_headroom(skb);
        else
                csstart = skb_headlen(skb);
 

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index e11eaf4cc269eb227a301cf6c69cd0f03a6c847b..a091a99ad263d7eaa3519dfccfd25d5891c60272 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -504,6 +504,7 @@ void tcp_v4_send_check(struct sock *sk, int len, struct sk_buff *skb)
        if (skb->ip_summed == CHECKSUM_PARTIAL) {
                th->check = ~tcp_v4_check(len, inet->saddr,
                                          inet->daddr, 0);
+               skb->csum_start = skb_transport_header(skb) - skb->head;
                skb->csum_offset = offsetof(struct tcphdr, check);
        } else {
                th->check = tcp_v4_check(len, inet->saddr, inet->daddr,
@@ -526,6 +527,7 @@ int tcp_v4_gso_send_check(struct sk_buff *skb)
 
        th->check = 0;
        th->check = ~tcp_v4_check(skb->len, iph->saddr, iph->daddr, 0);
+       skb->csum_start = skb_transport_header(skb) - skb->head;
        skb->csum_offset = offsetof(struct tcphdr, check);
        skb->ip_summed = CHECKSUM_PARTIAL;
        return 0;

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 71b0b60ba53881163687181cc20428642d04dd8a..5ad7a26e30917fea6b356268dd9dcf38a98cdfd9 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -427,6 +427,7 @@ static void udp4_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
                /*
                 * Only one fragment on the socket.
                 */
+               skb->csum_start = skb_transport_header(skb) - skb->head;
                skb->csum_offset = offsetof(struct udphdr, check);
                uh->check = ~csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, 0);
        } else {

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 4a55da079f5fb64ab515dfcc2e5b5f1d4f5d1f7d..7e824b97126d78d8a7e26baeaa28f18817152c20 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -950,6 +950,7 @@ static void tcp_v6_send_check(struct sock *sk, int len, struct sk_buff *skb)
 
        if (skb->ip_summed == CHECKSUM_PARTIAL) {
                th->check = ~csum_ipv6_magic(&np->saddr, &np->daddr, len, IPPROTO_TCP,  0);
+               skb->csum_start = skb_transport_header(skb) - skb->head;
                skb->csum_offset = offsetof(struct tcphdr, check);
        } else {
                th->check = csum_ipv6_magic(&np->saddr, &np->daddr, len, IPPROTO_TCP,
@@ -972,6 +973,7 @@ static int tcp_v6_gso_send_check(struct sk_buff *skb)
        th->check = 0;
        th->check = ~csum_ipv6_magic(&ipv6h->saddr, &ipv6h->daddr, skb->len,
                                     IPPROTO_TCP, 0);
+       skb->csum_start = skb_transport_header(skb) - skb->head;
        skb->csum_offset = offsetof(struct tcphdr, check);
        skb->ip_summed = CHECKSUM_PARTIAL;
        return 0;