Subject: [PATCH net-next 1/3] net: skb: carve the allocation out of skb_ext_add()

From: Jakub Kicinski <[email-masked]>
Date: Tue, 14 Feb 2023 19:43:53 -0800

Subsequent patches will try to add different skb_ext allocation
methods. Refactor skb_ext_add() so that most of its code moves
into a tail-called helper, and allocation can be easily swapped
out.

Signed-off-by: Jakub Kicinski <[email-masked]>
---
 net/core/skbuff.c | 52 ++++++++++++++++++++++++++++-------------------
 1 file changed, 31 insertions(+), 21 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 13ea10cf8544..6f0fc1f09536 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6672,26 +6672,13 @@ void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
 	return skb_ext_get_ptr(ext, id);
 }
 
-/**
- * skb_ext_add - allocate space for given extension, COW if needed
- * @skb: buffer
- * @id: extension to allocate space for
- *
- * Allocates enough space for the given extension.
- * If the extension is already present, a pointer to that extension
- * is returned.
- *
- * If the skb was cloned, COW applies and the returned memory can be
- * modified without changing the extension space of clones buffers.
- *
- * Returns pointer to the extension or NULL on allocation failure.
- */
-void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
+static void *skb_ext_add_finalize(struct sk_buff *skb, enum skb_ext_id id,
+				  struct skb_ext *new)
 {
-	struct skb_ext *new, *old = NULL;
 	unsigned int newlen, newoff;
+	struct skb_ext *old;
 
-	if (skb->active_extensions) {
+	if (!new) {
 		old = skb->extensions;
 
 		new = skb_ext_maybe_cow(old, skb->active_extensions);
@@ -6704,10 +6691,6 @@ void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
 		newoff = new->chunks;
 	} else {
 		newoff = SKB_EXT_CHUNKSIZEOF(*new);
-
-		new = __skb_ext_alloc(GFP_ATOMIC);
-		if (!new)
-			return NULL;
 	}
 
 	newlen = newoff + skb_ext_type_len[id];
@@ -6719,6 +6702,33 @@ void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
 	skb->active_extensions |= 1 << id;
 	return skb_ext_get_ptr(new, id);
 }
+
+/**
+ * skb_ext_add - allocate space for given extension, COW if needed
+ * @skb: buffer
+ * @id: extension to allocate space for
+ *
+ * Allocates enough space for the given extension.
+ * If the extension is already present, a pointer to that extension
+ * is returned.
+ *
+ * If the skb was cloned, COW applies and the returned memory can be
+ * modified without changing the extension space of clones buffers.
+ *
+ * Returns pointer to the extension or NULL on allocation failure.
+ */
+void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
+{
+	struct skb_ext *new = NULL;
+
+	if (!skb->active_extensions) {
+		new = __skb_ext_alloc(GFP_ATOMIC);
+		if (!new)
+			return NULL;
+	}
+
+	return skb_ext_add_finalize(skb, id, new);
+}
 EXPORT_SYMBOL(skb_ext_add);
 
 #ifdef CONFIG_XFRM
-- 
2.39.1