[patch] skbuff cleanup

[Andrew Morton <andrewm@xxxxxxxxxx>]

All the ethernet drivers do this in their Rx ISR::

        skb = dev_alloc_skb(length);
        ...
        skb_reserve(skb,2);     /* Force 16 byte alignment */

This patch collapses these into a single call
(dev_hdr_alloc_skb) which has the same number of
instructions as dev_alloc_skb.

So instead of the above we can simply use:

        skb = dev_hdr_alloc_skb(length, ETH_HLEN);

This function can be used for other L2's, however note that
it will align the L3 data on a 32 bit boundary only.  This
just happens to be a 16 byte boundary for Ethernet.



--- linux-2.3.99-pre1/include/linux/skbuff.h    Tue Mar 14 21:20:48 2000
+++ linux/include/linux/skbuff.h        Tue Mar 21 23:24:36 2000
@@ -626,6 +626,25 @@
        return skb;
 }
 
+/*
+ * Like dev_alloc_skb, except we are passed the length of the L2 layer's
+ * header (eg the Ethernet MAC header).  We allocate and then reserve 
+ * 0 to 3 bytes of additional room in the skb to ensure that the Layer 3
+ * data will start on a longword boundary
+ */
+
+extern __inline__ struct sk_buff *
+dev_hdr_alloc_skb(unsigned int length, const int proto_hdr_length)
+{
+       struct sk_buff *skb;
+       const int xlength = ((4 - (proto_hdr_length & 3)) & 3 ) + 16;
+
+       skb = alloc_skb(length+xlength, GFP_ATOMIC);
+       if (skb)
+               skb_reserve(skb,xlength);
+       return skb;
+}                                                                              
                     
+
 extern __inline__ struct sk_buff *
 skb_cow(struct sk_buff *skb, unsigned int headroom)
 {