On Thu, Aug 02, 2012 at 06:48:07PM +0200, Sasha Levin wrote:
> On 08/02/2012 06:15 PM, Josh Triplett wrote:
> > On Thu, Aug 02, 2012 at 03:04:19PM +0200, Sasha Levin wrote:
> >> On 08/02/2012 01:23 PM, Sasha Levin wrote:
> >>>> #define DEFINE_HASH_TABLE(name, length) struct hash_table name = {
> >>>> .count = length, .buckets = { [0 ... (length - 1)] = HLIST_HEAD_INIT } }
> >>> The limitation of this approach is that the struct hash_table variable
> >>> must be 'static', which is a bit limiting - see for example the use of
> >>> hashtable in 'struct user_namespace'.
> >>>
> >>
> >> What if we just use two possible decelerations? One of static structs and
> >> one for regular ones.
> >>
> >> struct hash_table {
> >> size_t bits;
> >> struct hlist_head buckets[];
> >> };
> >>
> >> #define DEFINE_HASHTABLE(name, bits) \
> >> union { \
> >> struct hash_table name; \
> >> struct { \
> >> size_t bits; \
> >
> > This shouldn't use "bits", since it'll get expanded to the macro
> > argument.
> >
> >> struct hlist_head buckets[1 << bits]; \
> >> } __name; \
> >
> > __##name
> >
> >> }
> >>
> >> #define DEFINE_STATIC_HASHTABLE(name, bit) \
> >> static struct hash_table name = { .bits = bit, \
> >> .buckets = { [0 ... (bit - 1)] = HLIST_HEAD_INIT } }
> >
> > You probably wanted to change that to [0 ... ((1 << bit) - 1)] , to
> > match DEFINE_HASHTABLE.
>
> I wrote it by hand and didn't compile test, will fix all of those.
>
> > Since your definition of DEFINE_HASHTABLE would also work fine when used
> > statically, why not just always use that?
> >
> > #define DEFINE_STATIC_HASHTABLE(name, bits) static DEFINE_HASHTABLE(name,
> > bits) = { .name.bits = bits }
>
> It will get defined fine, but it will be awkward to use. We'd need to pass
> anonymous union to all the functions that handle this hashtable, which isn't
> pretty.
No, it'll still use the anonymous union, so you'll still have a thing of
type "struct hash_table" with the given name, and you can use that name
with the hash-table functions.
- Josh Triplett
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