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/ # v1
Link: https://lore.kernel.org/r/163906889665.143852.10378009165231294456.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967085081.1823006.2218944206363626210.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021494847.640689.10109692261640524343.stgit@warthog.procyon.org.uk/ # v4

1 files changed, 33 insertions, 0 deletions

diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index f345bdb018ba..8fd39e7735fc 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -18,6 +18,39 @@
 #include <linux/seq_file.h>
 
 /*
+ * cache.c
+ */
+#ifdef CONFIG_PROC_FS
+extern const struct seq_operations fscache_caches_seq_ops;
+#endif
+struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache);
+void fscache_put_cache(struct fscache_cache *cache, enum fscache_cache_trace where);
+
+static inline enum fscache_cache_state fscache_cache_state(const struct fscache_cache *cache)
+{
+	return smp_load_acquire(&cache->state);
+}
+
+static inline bool fscache_cache_is_live(const struct fscache_cache *cache)
+{
+	return fscache_cache_state(cache) == FSCACHE_CACHE_IS_ACTIVE;
+}
+
+static inline void fscache_set_cache_state(struct fscache_cache *cache,
+					   enum fscache_cache_state new_state)
+{
+	smp_store_release(&cache->state, new_state);
+
+}
+
+static inline bool fscache_set_cache_state_maybe(struct fscache_cache *cache,
+						 enum fscache_cache_state old_state,
+						 enum fscache_cache_state new_state)
+{
+	return try_cmpxchg_release(&cache->state, &old_state, new_state);
+}
+
+/*
  * main.c
  */
 extern unsigned fscache_debug;