On Thu, Jan 20, 2011 at 5:10 PM, Kevin Wolf <kw...@redhat.com> wrote:
> +int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
> + void **table)
[...]
> +int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table)
> +{
> + int i;
> +
> + for (i = 0; i < c->size; i++) {
> + if (c->entries[i].table == *table) {
> + goto found;
> + }
> + }
> + return -ENOENT;
> +
> +found:
Using void **table instead of a QCowCacheEntry struct has two disadvantages:
1. The fact that you're holding a reference is not explicit. It makes
it unclear whether we're dealing with a cached table or not. In user
code, uint64_t *l2_table doesn't tell me whether this table is in the
cache or is being managed outside the cache. Therefore it's hard to
check that the necessary qcow2_cache_put() calls are being made.
2. qcow2-cache.c needs to scan through the cache linearly looking for
void *table on every call. If the user holds an explicit
QCowCacheEntry then no lookup is necessary.
Stefan
