fscache: Implement cache registration
Implement a register of caches and provide functions to manage it.
Two functions are provided for the cache backend to use:
(1) Acquire a cache cookie:
struct fscache_cache *fscache_acquire_cache(const char *name)
This gets the cache cookie for a cache of the specified name and moves
it to the preparation state. If a nameless cache cookie exists, that
will be given this name and used.
(2) Relinquish a cache cookie:
void fscache_relinquish_cache(struct fscache_cache *cache);
This relinquishes a cache cookie, cleans it and makes it available if
it's still referenced by a network filesystem.
Note that network filesystems don't deal with cache cookies directly, but
rather go straight to the volume registration.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819587157.215744.13523139317322503286.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163906889665.143852.10378009165231294456.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163967085081.1823006.2218944206363626210.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/164021494847.640689.10109692261640524343.stgit@warthog.procyon.org.uk/