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rhashtable: add function to replace an element 

Add the rhashtable_replace_fast function. This replaces one object in
the table with another atomically. The hashes of the new and old objects
must be equal.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Herbert 2015-12-15 15:41:36 -08:00 committed by David S. Miller
parent 33f11d1614
commit 3502cad73c
1 changed files with 82 additions and 0 deletions
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82
include/linux/rhashtable.h
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@ -819,4 +819,86 @@ static inline int rhashtable_remove_fast(
return err;
}
/* Internal function, please use rhashtable_replace_fast() instead */
static inline int __rhashtable_replace_fast(
struct rhashtable *ht, struct bucket_table *tbl,
struct rhash_head *obj_old, struct rhash_head *obj_new,
const struct rhashtable_params params)
{
struct rhash_head __rcu **pprev;
struct rhash_head *he;
spinlock_t *lock;
unsigned int hash;
int err = -ENOENT;
/* Minimally, the old and new objects must have same hash
* (which should mean identifiers are the same).
*/
hash = rht_head_hashfn(ht, tbl, obj_old, params);
if (hash != rht_head_hashfn(ht, tbl, obj_new, params))
return -EINVAL;
lock = rht_bucket_lock(tbl, hash);
spin_lock_bh(lock);
pprev = &tbl->buckets[hash];
rht_for_each(he, tbl, hash) {
if (he != obj_old) {
pprev = &he->next;
continue;
}
rcu_assign_pointer(obj_new->next, obj_old->next);
rcu_assign_pointer(*pprev, obj_new);
err = 0;
break;
}
spin_unlock_bh(lock);
return err;
}
/**
* rhashtable_replace_fast - replace an object in hash table
* @ht: hash table
* @obj_old: pointer to hash head inside object being replaced
* @obj_new: pointer to hash head inside object which is new
* @params: hash table parameters
*
* Replacing an object doesn't affect the number of elements in the hash table
* or bucket, so we don't need to worry about shrinking or expanding the
* table here.
*
* Returns zero on success, -ENOENT if the entry could not be found,
* -EINVAL if hash is not the same for the old and new objects.
*/
static inline int rhashtable_replace_fast(
struct rhashtable *ht, struct rhash_head *obj_old,
struct rhash_head *obj_new,
const struct rhashtable_params params)
{
struct bucket_table *tbl;
int err;
rcu_read_lock();
tbl = rht_dereference_rcu(ht->tbl, ht);
/* Because we have already taken (and released) the bucket
* lock in old_tbl, if we find that future_tbl is not yet
* visible then that guarantees the entry to still be in
* the old tbl if it exists.
*/
while ((err = __rhashtable_replace_fast(ht, tbl, obj_old,
obj_new, params)) &&
(tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
;
rcu_read_unlock();
return err;
}
#endif /* _LINUX_RHASHTABLE_H */