[RFC PATCH 04/11] net: add simple socket-like dst cache helpers

[Paolo Abeni]

It will be used by later patches to reduce code duplication.

Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 include/net/dst.h | 20 ++++++++++++++++++++
 net/core/dst.c    | 12 ++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/net/dst.h b/include/net/dst.h
index 93568bd0a352..4fcca0e368c6 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -485,6 +485,26 @@ static inline struct dst_entry *dst_check(struct dst_entry 
*dst, u32 cookie)
        return dst;
 }
 
+/* update the cache with dst, assuming the latter already carries a refcount */
+static inline bool __dst_update(struct dst_entry **cache, struct dst_entry 
*dst)
+{
+       struct dst_entry *old = xchg(cache, dst);
+
+       dst_release(old);
+       return old != dst;
+}
+bool dst_update(struct dst_entry **cache, struct dst_entry *dst);
+static inline struct dst_entry *dst_access(struct dst_entry **cache,
+                                             u32 cookie)
+{
+       struct dst_entry *dst = READ_ONCE(*cache);
+
+       if (!dst)
+               return NULL;
+
+       return dst_check(dst, cookie);
+}
+
 /* Flags for xfrm_lookup flags argument. */
 enum {
        XFRM_LOOKUP_ICMP = 1 << 0,
diff --git a/net/core/dst.c b/net/core/dst.c
index a6c47da7d0f8..4076f9af45d7 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -205,6 +205,18 @@ void dst_release_immediate(struct dst_entry *dst)
 }
 EXPORT_SYMBOL(dst_release_immediate);
 
+/* update the cache with dst, assuming the latter does not carry a refcount */
+bool dst_update(struct dst_entry **cache, struct dst_entry *dst)
+{
+       if (likely(*cache == dst))
+               return false;
+
+       if (dst_hold_safe(dst))
+               return __dst_update(cache, dst);
+       return false;
+}
+EXPORT_SYMBOL_GPL(dst_update);
+
 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
 {
        struct dst_metrics *p = kmalloc(sizeof(*p), GFP_ATOMIC);
-- 
2.13.5