net: cleanup and document skb fclone layout

Lets use a proper structure to clearly document and implement
skb fast clones.

Then, we might experiment more easily alternative layouts.

This patch adds a new skb_fclone_busy() helper, used by tcp and xfrm,
to stop leaking of implementation details.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 262efdbc346b..d8f7d74d5a4d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -781,6 +781,31 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
                                      int *errcode,
                                      gfp_t gfp_mask);
 
+/* Layout of fast clones : [skb1][skb2][fclone_ref] */
+struct sk_buff_fclones {
+        struct sk_buff  skb1;
+
+        struct sk_buff  skb2;
+
+        atomic_t        fclone_ref;
+};
+
+/**
+ *      skb_fclone_busy - check if fclone is busy
+ *      @skb: buffer
+ *
+ * Returns true is skb is a fast clone, and its clone is not freed.
+ */
+static inline bool skb_fclone_busy(const struct sk_buff *skb)
+{
+        const struct sk_buff_fclones *fclones;
+
+        fclones = container_of(skb, struct sk_buff_fclones, skb1);
+
+        return skb->fclone == SKB_FCLONE_ORIG &&
+               fclones->skb2.fclone == SKB_FCLONE_CLONE;
+}
+
 static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
                                                gfp_t priority)
 {