skb: add helpers to allocate ext independently from sk_buff

Currently we can allocate the extension only after the skb,
this change allows the user to do the opposite, will simplify
allocation failure handling from MPTCP.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f5c27600b410baf72bc053b88c7c19278ef4450b..016b3c4ab99a90a570672c941e3f9f1c143acdd7 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4120,6 +4120,9 @@ struct skb_ext {
        char data[0] __aligned(8);
 };
 
+struct skb_ext *__skb_ext_alloc(void);
+void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
+                   struct skb_ext *ext);
 void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id);
 void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id);
 void __skb_ext_put(struct skb_ext *ext);

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a4106da23c343a1ed6aba5fdd1956a2407d38317..48a7029529c970787e3ee705e2bf087da2a84329 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5987,7 +5987,14 @@ static void *skb_ext_get_ptr(struct skb_ext *ext, enum skb_ext_id id)
        return (void *)ext + (ext->offset[id] * SKB_EXT_ALIGN_VALUE);
 }
 
-static struct skb_ext *skb_ext_alloc(void)
+/**
+ * __skb_ext_alloc - allocate a new skb extensions storage
+ *
+ * Returns the newly allocated pointer. The pointer can later attached to a
+ * skb via __skb_ext_set().
+ * Note: caller must handle the skb_ext as an opaque data.
+ */
+struct skb_ext *__skb_ext_alloc(void)
 {
        struct skb_ext *new = kmem_cache_alloc(skbuff_ext_cache, GFP_ATOMIC);
 
@@ -6027,6 +6034,30 @@ static struct skb_ext *skb_ext_maybe_cow(struct skb_ext *old,
        return new;
 }
 
+/**
+ * __skb_ext_set - attach the specified extension storage to this skb
+ * @skb: buffer
+ * @id: extension id
+ * @ext: extension storage previously allocated via __skb_ext_alloc()
+ *
+ * Existing extensions, if any, are cleared.
+ *
+ * Returns the pointer to the extension.
+ */
+void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
+                   struct skb_ext *ext)
+{
+       unsigned int newlen, newoff = SKB_EXT_CHUNKSIZEOF(*ext);
+
+       skb_ext_put(skb);
+       newlen = newoff + skb_ext_type_len[id];
+       ext->chunks = newlen;
+       ext->offset[id] = newoff;
+       skb->extensions = ext;
+       skb->active_extensions = 1 << id;
+       return skb_ext_get_ptr(ext, id);
+}
+
 /**
  * skb_ext_add - allocate space for given extension, COW if needed
  * @skb: buffer
@@ -6060,7 +6091,7 @@ void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
        } else {
                newoff = SKB_EXT_CHUNKSIZEOF(*new);
 
-               new = skb_ext_alloc();
+               new = __skb_ext_alloc();
                if (!new)
                        return NULL;
        }