net: add skb_dst_set_noref_force

Rename skb_dst_set_noref to __skb_dst_set_noref and
add force flag as suggested by David Miller. The new wrapper
skb_dst_set_noref_force will force dst entries that are not
cached to be attached as skb dst without taking reference
as long as provided dst is reclaimed after RCU grace period.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off by: Hans Schillstrom <hans@schillstrom.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 34 insertions, 1 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 878e0ee81068..364e2440a7ee 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -575,7 +575,40 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
         skb->_skb_refdst = (unsigned long)dst;
 }
 
-extern void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst);
+extern void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst,
+                                bool force);
+
+/**
+ * skb_dst_set_noref - sets skb dst, hopefully, without taking reference
+ * @skb: buffer
+ * @dst: dst entry
+ *
+ * Sets skb dst, assuming a reference was not taken on dst.
+ * If dst entry is cached, we do not take reference and dst_release
+ * will be avoided by refdst_drop. If dst entry is not cached, we take
+ * reference, so that last dst_release can destroy the dst immediately.
+ */
+static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
+{
+        __skb_dst_set_noref(skb, dst, false);
+}
+
+/**
+ * skb_dst_set_noref_force - sets skb dst, without taking reference
+ * @skb: buffer
+ * @dst: dst entry
+ *
+ * Sets skb dst, assuming a reference was not taken on dst.
+ * No reference is taken and no dst_release will be called. While for
+ * cached dsts deferred reclaim is a basic feature, for entries that are
+ * not cached it is caller's job to guarantee that last dst_release for
+ * provided dst happens when nobody uses it, eg. after a RCU grace period.
+ */
+static inline void skb_dst_set_noref_force(struct sk_buff *skb,
+                                           struct dst_entry *dst)
+{
+        __skb_dst_set_noref(skb, dst, true);
+}
 
 /**
  * skb_dst_is_noref - Test if skb dst isn't refcounted