vlan: avoid header copying and linearisation where possible

- vlan_dev_reorder_header() is only called on the receive path after
  calling skb_share_check(). This means we can use skb_cow() since
  all we need is a writable header.

- vlan_dev_hard_header() includes a work-around for some apparently
  broken out of tree MPLS code. The hard_header functions can expect
  to always have a headroom of at least there own hard_header_len
  available, so the reallocation check is unnecessary.

- __vlan_put_tag() can use skb_cow_head() to avoid the skb_unshare()
  copy when the header is writable.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index d36515d..93f5d9b 100644 (file)
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -185,22 +185,10 @@ static inline struct sk_buff *__vlan_put_tag(struct sk_buff *skb, u16 vlan_tci)
 {
        struct vlan_ethhdr *veth;
 
-       if (skb_headroom(skb) < VLAN_HLEN) {
-               struct sk_buff *sk_tmp = skb;
-               skb = skb_realloc_headroom(sk_tmp, VLAN_HLEN);
-               kfree_skb(sk_tmp);
-               if (!skb) {
-                       printk(KERN_ERR "vlan: failed to realloc headroom\n");
-                       return NULL;
-               }
-       } else {
-               skb = skb_unshare(skb, GFP_ATOMIC);
-               if (!skb) {
-                       printk(KERN_ERR "vlan: failed to unshare skbuff\n");
-                       return NULL;
-               }
+       if (skb_cow_head(skb, VLAN_HLEN) < 0) {
+               kfree_skb(skb);
+               return NULL;
        }
-
        veth = (struct vlan_ethhdr *)skb_push(skb, VLAN_HLEN);
 
        /* Move the mac addresses to the beginning of the new header. */

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index 2ccac6b..b6e52c0 100644 (file)
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -74,11 +74,8 @@ static int vlan_dev_rebuild_header(struct sk_buff *skb)
 static inline struct sk_buff *vlan_check_reorder_header(struct sk_buff *skb)
 {
        if (vlan_dev_info(skb->dev)->flags & VLAN_FLAG_REORDER_HDR) {
-               if (skb_shared(skb) || skb_cloned(skb)) {
-                       struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
-                       kfree_skb(skb);
-                       skb = nskb;
-               }
+               if (skb_cow(skb, skb_headroom(skb)) < 0)
+                       skb = NULL;
                if (skb) {
                        /* Lifted from Gleb's VLAN code... */
                        memmove(skb->data - ETH_HLEN,
@@ -262,12 +259,14 @@ static int vlan_dev_hard_header(struct sk_buff *skb, struct net_device *dev,
        u16 vlan_tci = 0;
        int rc = 0;
        int build_vlan_header = 0;
-       struct net_device *vdev = dev;
 
        pr_debug("%s: skb: %p type: %hx len: %u vlan_id: %hx, daddr: %p\n",
                 __func__, skb, type, len, vlan_dev_info(dev)->vlan_id,
                 daddr);
 
+       if (WARN_ON(skb_headroom(skb) < dev->hard_header_len))
+               return -ENOSPC;
+
        /* build vlan header only if re_order_header flag is NOT set.  This
         * fixes some programs that get confused when they see a VLAN device
         * sending a frame that is VLAN encoded (the consensus is that the VLAN
@@ -316,29 +315,6 @@ static int vlan_dev_hard_header(struct sk_buff *skb, struct net_device *dev,
 
        dev = vlan_dev_info(dev)->real_dev;
 
-       /* MPLS can send us skbuffs w/out enough space. This check will grow
-        * the skb if it doesn't have enough headroom. Not a beautiful solution,
-        * so I'll tick a counter so that users can know it's happening...
-        * If they care...
-        */
-
-       /* NOTE: This may still break if the underlying device is not the final
-        * device (and thus there are more headers to add...) It should work for
-        * good-ole-ethernet though.
-        */
-       if (skb_headroom(skb) < dev->hard_header_len) {
-               struct sk_buff *sk_tmp = skb;
-               skb = skb_realloc_headroom(sk_tmp, dev->hard_header_len);
-               kfree_skb(sk_tmp);
-               if (skb == NULL) {
-                       struct net_device_stats *stats = &vdev->stats;
-                       stats->tx_dropped++;
-                       return -ENOMEM;
-               }
-               vlan_dev_info(vdev)->cnt_inc_headroom_on_tx++;
-               pr_debug("%s: %s: had to grow skb\n", __func__, vdev->name);
-       }
-
        if (build_vlan_header) {
                /* Now make the underlying real hard header */
                rc = dev_hard_header(skb, dev, ETH_P_8021Q, daddr, saddr,