[PATCH nf-next 1/2] rhashtable: add rhashtable_lookup_get_insert_key()

[Pablo Neira Ayuso]

This patch modifies __rhashtable_insert_fast() so it returns the
existing element that clashes with the one that you want to insert.
This adds a new rhashtable_lookup_get_insert_key() interface to fetch
this existing element.

nf_tables needs this change to improve handling of EEXIST cases via
honoring the NLM_F_EXCL flag and by checking if the data part of the
mapping matches what we have.

Cc: Herbert Xu <herb...@gondor.apana.org.au>
Cc: Thomas Graf <tg...@suug.ch>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---

 include/linux/rhashtable.h | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 3eef080..a632cf0 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -566,7 +566,7 @@ restart:
 /* Internal function, please use rhashtable_insert_fast() instead */
 static inline int __rhashtable_insert_fast(
        struct rhashtable *ht, const void *key, struct rhash_head *obj,
-       const struct rhashtable_params params)
+       const struct rhashtable_params params, void **data)
 {
        struct rhashtable_compare_arg arg = {
                .ht = ht,
@@ -630,8 +630,11 @@ slow_path:
                if (key &&
                    unlikely(!(params.obj_cmpfn ?
                               params.obj_cmpfn(&arg, rht_obj(ht, head)) :
-                              rhashtable_compare(&arg, rht_obj(ht, head)))))
+                              rhashtable_compare(&arg, rht_obj(ht, head))))) {
+                       if (data)
+                               *data = rht_obj(ht, head);
                        goto out;
+               }
                if (!--elasticity)
                        goto slow_path;
        }
@@ -675,7 +678,7 @@ static inline int rhashtable_insert_fast(
        struct rhashtable *ht, struct rhash_head *obj,
        const struct rhashtable_params params)
 {
-       return __rhashtable_insert_fast(ht, NULL, obj, params);
+       return __rhashtable_insert_fast(ht, NULL, obj, params, NULL);
 }
 
 /**
@@ -708,7 +711,7 @@ static inline int rhashtable_lookup_insert_fast(
        BUG_ON(ht->p.obj_hashfn);
 
        return __rhashtable_insert_fast(ht, key + ht->p.key_offset, obj,
-                                       params);
+                                       params, NULL);
 }
 
 /**
@@ -739,7 +742,26 @@ static inline int rhashtable_lookup_insert_key(
 {
        BUG_ON(!ht->p.obj_hashfn || !key);
 
-       return __rhashtable_insert_fast(ht, key, obj, params);
+       return __rhashtable_insert_fast(ht, key, obj, params, NULL);
+}
+
+/**
+ * rhashtable_lookup_get_insert_key - lookup and insert object into hash table
+ * @ht:                hash table
+ * @obj:       pointer to hash head inside object
+ * @params:    hash table parameters
+ * @data:      pointer to element data already in hashes
+ *
+ * Just like rhashtable_lookup_insert_key(), but it returns the matching
+ * element in case that it already exists in the hashes.
+ */
+static inline int rhashtable_lookup_get_insert_key(
+       struct rhashtable *ht, const void *key, struct rhash_head *obj,
+       const struct rhashtable_params params, void **data)
+{
+       BUG_ON(!ht->p.obj_hashfn || !key);
+
+       return __rhashtable_insert_fast(ht, key, obj, params, data);
 }
 
 /* Internal function, please use rhashtable_remove_fast() instead */
-- 
2.1.4

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