[dpdk-users] Mismatch between return value and documentation for `rte_hash_lookup_data` (cuckoo hashing implementation)

[Petr Houska <t-pehous@microsoft.com>]

Documentation for `rte_hash_lookup_data` specifies that this method returns 0 on
successful data lookup or positive error code on not-found / wrong parameters.  In
reality it returns positive index of found data on success and negative error on error,
in essence it behaves the same as  (i.e. the same as  rte_hash_lookup while also (correctly)
populating the data pointer).

rte_cuckoo_hash.c: 733
```c
int
rte_hash_lookup_data(const struct rte_hash *h, const void *key, void **data)
{
                RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
                return __rte_hash_lookup_with_hash(h, key, rte_hash_hash(h, key), data);
}
```

Rte_cuckoo_hash.c: 693
```c
static inline int32_t
__rte_hash_lookup_with_hash(const struct rte_hash *h, const void *key,
                                                                                hash_sig_t sig, void **data)
{
                ...
                                                                /*
                                                                * Return index where key is stored,
                                                                * subtracting the first dummy index
                                                                */
                                                                return bkt->key_idx[i] - 1;
```

DPDK version 18.05 release.

PS: I'm not sure whether this email shouldn't have gone to dev@dpdk.org<mailto:dev@dpdk.org>,
please accept my apology if that's the case.

Petr Houska
Azure Intern