net: add function to allocate sk_buff head without data area

Add a function to allocate a sk_buff head without any data. This will
be used by memory mapped netlink to attach data from the mmaped area
to the skb.

Additionally change skb_release_all() to check whether the skb has a
data area to allow the skb destructor to clear the data pointer in case
only a head has been allocated.

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

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f5bed7b..2e0ced1 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -651,6 +651,12 @@ static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
        return __alloc_skb(size, priority, SKB_ALLOC_FCLONE, NUMA_NO_NODE);
 }
 
+extern struct sk_buff *__alloc_skb_head(gfp_t priority, int node);
+static inline struct sk_buff *alloc_skb_head(gfp_t priority)
+{
+       return __alloc_skb_head(priority, -1);
+}
+
 extern struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
 extern int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask);
 extern struct sk_buff *skb_clone(struct sk_buff *skb,

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a92d9e7..898cf5c 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -179,6 +179,33 @@ out:
  *
  */
 
+struct sk_buff *__alloc_skb_head(gfp_t gfp_mask, int node)
+{
+       struct sk_buff *skb;
+
+       /* Get the HEAD */
+       skb = kmem_cache_alloc_node(skbuff_head_cache,
+                                   gfp_mask & ~__GFP_DMA, node);
+       if (!skb)
+               goto out;
+
+       /*
+        * Only clear those fields we need to clear, not those that we will
+        * actually initialise below. Hence, don't put any more fields after
+        * the tail pointer in struct sk_buff!
+        */
+       memset(skb, 0, offsetof(struct sk_buff, tail));
+       skb->data = NULL;
+       skb->truesize = sizeof(struct sk_buff);
+       atomic_set(&skb->users, 1);
+
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+       skb->mac_header = ~0U;
+#endif
+out:
+       return skb;
+}
+
 /**
  *     __alloc_skb     -       allocate a network buffer
  *     @size: size to allocate
@@ -584,7 +611,8 @@ static void skb_release_head_state(struct sk_buff *skb)
 static void skb_release_all(struct sk_buff *skb)
 {
        skb_release_head_state(skb);
-       skb_release_data(skb);
+       if (likely(skb->data))
+               skb_release_data(skb);
 }
 
 /**