FS-Cache: Add cache tag handling

Implement two features of FS-Cache:

 (1) The ability to request and release cache tags - names by which a cache may
     be known to a netfs, and thus selected for use.

 (2) An internal function by which a cache is selected by consulting the netfs,
     if the netfs wishes to be consulted.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index feb3b0e0af4d..9584c094d69f 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -173,6 +173,8 @@ struct fscache_netfs {
  * - these are undefined symbols when FS-Cache is not configured and the
  *   optimiser takes care of not using them
  */
+extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);
+extern void __fscache_release_cache_tag(struct fscache_cache_tag *);
 
 /**
  * fscache_register_netfs - Register a filesystem as desiring caching services
@@ -218,7 +220,10 @@ void fscache_unregister_netfs(struct fscache_netfs *netfs)
 static inline
 struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
 {
-        return NULL;
+        if (fscache_available())
+                return __fscache_lookup_cache_tag(name);
+        else
+                return NULL;
 }
 
 /**
@@ -233,6 +238,8 @@ struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
 static inline
 void fscache_release_cache_tag(struct fscache_cache_tag *tag)
 {
+        if (fscache_available())
+                __fscache_release_cache_tag(tag);
 }
 
 /**