[NET]: Avoid allocating skb in skb_pad

First of all it is unnecessary to allocate a new skb in skb_pad since
the existing one is not shared.  More importantly, our hard_start_xmit
interface does not allow a new skb to be allocated since that breaks
requeueing.

This patch uses pskb_expand_head to expand the existing skb and linearize
it if needed.  Actually, someone should sift through every instance of
skb_pad on a non-linear skb as they do not fit the reasons why this was
originally created.

Incidentally, this fixes a minor bug when the skb is cloned (tcpdump,
TCP, etc.).  As it is skb_pad will simply write over a cloned skb.  Because
of the position of the write it is unlikely to cause problems but still
it's best if we don't do it.

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

1 files changed, 2 insertions, 5 deletions

diff --git a/drivers/net/epic100.c b/drivers/net/epic100.c
index 8d680ce600d7..724d7dc35fa3 100644
--- a/drivers/net/epic100.c
+++ b/drivers/net/epic100.c
@@ -1027,11 +1027,8 @@ static int epic_start_xmit(struct sk_buff *skb, struct net_device *dev)
         u32 ctrl_word;
         unsigned long flags;
 
-        if (skb->len < ETH_ZLEN) {
-                skb = skb_padto(skb, ETH_ZLEN);
-                if (skb == NULL)
-                        return 0;
-        }
+        if (skb_padto(skb, ETH_ZLEN))
+                return 0;
 
         /* Caution: the write order is important here, set the field with the
            "ownership" bit last. */