2 files changed, 50 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index fe864885c1ed..abad8a0941e8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -540,6 +540,7 @@ extern void consume_skb(struct sk_buff *skb);
 extern void            __kfree_skb(struct sk_buff *skb);
 extern struct sk_buff *__alloc_skb(unsigned int size,
                                    gfp_t priority, int fclone, int node);
+extern struct sk_buff *build_skb(void *data);
 static inline struct sk_buff *alloc_skb(unsigned int size,
                                         gfp_t priority)
 {
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 18a3cebb753d..8d2c5b32f172 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -245,6 +245,55 @@ nodata:
 EXPORT_SYMBOL(__alloc_skb);
 
 /**
+ * build_skb - build a network buffer
+ * @data: data buffer provided by caller
+ *
+ * Allocate a new &sk_buff. Caller provides space holding head and
+ * skb_shared_info. @data must have been allocated by kmalloc()
+ * The return is the new skb buffer.
+ * On a failure the return is %NULL, and @data is not freed.
+ * Notes :
+ *  Before IO, driver allocates only data buffer where NIC put incoming frame
+ *  Driver should add room at head (NET_SKB_PAD) and
+ *  MUST add room at tail (SKB_DATA_ALIGN(skb_shared_info))
+ *  After IO, driver calls build_skb(), to allocate sk_buff and populate it
+ *  before giving packet to stack.
+ *  RX rings only contains data buffers, not full skbs.
+ */
+struct sk_buff *build_skb(void *data)
+{
+        struct skb_shared_info *shinfo;
+        struct sk_buff *skb;
+        unsigned int size;
+
+        skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC);
+        if (!skb)
+                return NULL;
+
+        size = ksize(data) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
+        memset(skb, 0, offsetof(struct sk_buff, tail));
+        skb->truesize = SKB_TRUESIZE(size);
+        atomic_set(&skb->users, 1);
+        skb->head = data;
+        skb->data = data;
+        skb_reset_tail_pointer(skb);
+        skb->end = skb->tail + size;
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+        skb->mac_header = ~0U;
+#endif
+
+        /* make sure we initialize shinfo sequentially */
+        shinfo = skb_shinfo(skb);
+        memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
+        atomic_set(&shinfo->dataref, 1);
+        kmemcheck_annotate_variable(shinfo->destructor_arg);
+
+        return skb;
+}
+EXPORT_SYMBOL(build_skb);
+
+/**
  *      __netdev_alloc_skb - allocate an skbuff for rx on a specific device
  *      @dev: network device to receive on
  *      @length: length to allocate