Re: [dpdk-dev] [PATCH] hash: added rte_hash_keys to extract all keys

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Tomas,

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Tomas Vestelind
> Sent: Tuesday, August 12, 2014 10:48 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH] hash: added rte_hash_keys to extract all keys
> 
> I added a function which extracts all the configured keys in a hash map.
> This is good to have when debugging and printing data store in hash
> maps.
> 
> Signed-off-by: Tomas Vestelind <tomas.vestelind@gmail.com>
> ---
>  lib/librte_hash/rte_hash.c |   26 ++++++++++++++++++++++++++
>  lib/librte_hash/rte_hash.h |   15 +++++++++++++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/lib/librte_hash/rte_hash.c b/lib/librte_hash/rte_hash.c
> index d02b6b4..2108c4f 100644
> --- a/lib/librte_hash/rte_hash.c
> +++ b/lib/librte_hash/rte_hash.c
> @@ -481,3 +481,29 @@ rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
> 
>  	return 0;
>  }
> +
> +unsigned int
> +rte_hash_keys(const struct rte_hash *h, void *keys)
> +{
> +    unsigned int found_keys = 0;
> +    unsigned int bucket, entry;
> +
> +    /* Go through each bucket and all its entries */
> +    for (bucket = 0; bucket < h->num_buckets; bucket++) {
> +        const hash_sig_t *sig = get_sig_tbl_bucket(h, bucket);
> +
> +        for (entry = 0; entry < h->bucket_entries; entry++) {
> +            /* If the signature is valid, find and save the corresponding key */
> +            if (sig[entry] != NULL_SIGNATURE) {
> +               uint8_t *key_bucket = get_key_tbl_bucket(h, bucket);
> +               void *key = get_key_from_bucket(h, key_bucket, entry);
> +               rte_memcpy(keys, key, h->key_len);
> +
> +               keys = (uint8_t* )keys + h->key_len;
> +               found_keys++;
> +            }
> +        }
> +    }

I suppose we need to add one extra parameter:  keys_size (size of the buffer provided) and inside the loop check that we wouldn't go beyond it.
Also it would probably helpful to have a function that would return to the user size of buffer needed to sore all keys from the hash.
What you probably can do: implement a function that would iterate over all elements in the hash table and for each of them call a callback (taken as an argument).
Then all these functions and rte_hash_clear() could be implemented on top of it.
Something like:

typedef int (*rte_hash_elem_iter_t)(const struct rte_hash*hash, const void *key, void *user_arg);
void
rte_hash_elem_iterate(const struct rte_hash *h, rte_hash_key_elem_t iter, void *arg)
{
   ...
}

About rte_hash_clear(const struct rte_hash *h) - can't we just do memset(h->sig_tbl, NULL_SIGNATURE, sig_tbl_size);?
BTW, why it is pointer to the const strucuture if we modifying it?

> +
> +    return found_keys;
> +}
> diff --git a/lib/librte_hash/rte_hash.h b/lib/librte_hash/rte_hash.h
> index 2ecaf1a..e0fb28f 100644
> --- a/lib/librte_hash/rte_hash.h
> +++ b/lib/librte_hash/rte_hash.h
> @@ -303,6 +303,21 @@ rte_hash_hash(const struct rte_hash *h, const void *key)
>  int
>  rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
>  		      uint32_t num_keys, int32_t *positions);
> +
> +/**
> + * Copy the hash table keys to the supplied list of keys.
> + * This operation is multi-thread safe.
> + *
> + * @param h
> + *   Hash table to look in.
> + * @param keys
> + *   A pointer to a list of where keys will be written.
> + *   Must be large enough to fit a potentially full hash map.
> + * @return
> + *   The number of found keys.
> + */
> +unsigned int
> +rte_hash_keys(const struct rte_hash *h, void *keys);
>  #ifdef __cplusplus
>  }
>  #endif
> --
> 1.7.10.4