Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

Tejun Heo
2012-08-03T17:15:15Z

Hello, Sasha.

On Fri, Aug 03, 2012 at 04:23:02PM +0200, Sasha Levin wrote:
> +#define DEFINE_STATIC_HASHTABLE(n, b) \
> + static struct hash_table n = { .bits = (b), \
> + .buckets = { [0 ... ((1 << (b)) - 1)] = HLIST_HEAD_INIT } }

What does this "static" mean?

> +#define DEFINE_HASHTABLE(n, b) \
> + union { \
> + struct hash_table n; \
> + struct { \
> + size_t bits; \
> + struct hlist_head buckets[1 << (b)]; \
> + } __##n ; \
> + };

Is this supposed to be embedded in struct definition? If so, the name
is rather misleading as DEFINE_* is supposed to define and initialize
stand-alone constructs. Also, for struct members, simply putting hash
entries after struct hash_table should work.

Wouldn't using DEFINE_HASHTABLE() for the first macro and
DEFINE_HASHTABLE_MEMBER() for the latter be better?

> +#define HASH_BITS(name) ((name)->bits)
> +#define HASH_SIZE(name) (1 << (HASH_BITS(name)))
> +
> +__attribute__ ((unused))

Are we using __attribute__((unused)) for functions defined in headers
instead of static inline now? If so, why?

> +static void hash_init(struct hash_table *ht, size_t bits)
> +{
> + size_t i;

I would prefer int here but no biggie.

> + ht->bits = bits;
> + for (i = 0; i < (1 << bits); i++)
> + INIT_HLIST_HEAD(&ht->buckets[i]);
> +}
> +
> +static void hash_add(struct hash_table *ht, struct hlist_node *node, long key)
> +{
> + hlist_add_head(node,
> + &ht->buckets[hash_long((unsigned long)key, HASH_BITS(ht))]);
> +}
> +
> +
> +#define hash_get(name, key, type, member, cmp_fn) \
> +({ \
> + struct hlist_node *__node; \
> + typeof(key) __key = key; \
> + type *__obj = NULL; \
> + hlist_for_each_entry(__obj, __node, &(name)->buckets[ \
> + hash_long((unsigned long) __key, \
> + HASH_BITS(name))], member) \
> + if (cmp_fn(__obj, __key)) \
> + break; \
> + __obj; \
> +})

As opposed to using hash_for_each_possible(), how much difference does
this make? Is it really worthwhile?

Thanks.

--
tejun