FS-Cache: Add interface to check consistency of a cached object
Extend the fscache netfs API so that the netfs can ask as to whether a cache
object is up to date with respect to its corresponding netfs object:
int fscache_check_consistency(struct fscache_cookie *cookie)
This will call back to the netfs to check whether the auxiliary data associated
with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it
may also return -ENOMEM and -ERESTARTSYS.
The backends now have to implement a mandatory operation pointer:
int (*check_consistency)(struct fscache_object *object)
that corresponds to the above API call. FS-Cache takes care of pinning the
object and the cookie in memory and managing this call with respect to the
object state.
Original-author: Hongyi Jia <jiayisuse@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Hongyi Jia <jiayisuse@gmail.com>
cc: Milosz Tanski <milosz@adfin.com>
diff --git a/Documentation/filesystems/caching/backend-api.txt b/Documentation/filesystems/caching/backend-api.txt
index d78bab9..277d1e8 100644
--- a/Documentation/filesystems/caching/backend-api.txt
+++ b/Documentation/filesystems/caching/backend-api.txt
@@ -299,6 +299,15 @@
enough space in the cache to permit this.
+ (*) Check coherency state of an object [mandatory]:
+
+ int (*check_consistency)(struct fscache_object *object)
+
+ This method is called to have the cache check the saved auxiliary data of
+ the object against the netfs's idea of the state. 0 should be returned
+ if they're consistent and -ESTALE otherwise. -ENOMEM and -ERESTARTSYS
+ may also be returned.
+
(*) Update object [mandatory]:
int (*update_object)(struct fscache_object *object)
diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt
index 97e6c0ec..12b3442 100644
--- a/Documentation/filesystems/caching/netfs-api.txt
+++ b/Documentation/filesystems/caching/netfs-api.txt
@@ -32,7 +32,7 @@
(9) Setting the data file size
(10) Page alloc/read/write
(11) Page uncaching
- (12) Index and data file update
+ (12) Index and data file consistency
(13) Miscellaneous cookie operations
(14) Cookie unregistration
(15) Index invalidation
@@ -690,9 +690,18 @@
error is returned.
-==========================
-INDEX AND DATA FILE UPDATE
-==========================
+===============================
+INDEX AND DATA FILE CONSISTENCY
+===============================
+
+To find out whether auxiliary data for an object is up to data within the
+cache, the following function can be called:
+
+ int fscache_check_consistency(struct fscache_cookie *cookie)
+
+This will call back to the netfs to check whether the auxiliary data associated
+with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it
+may also return -ENOMEM and -ERESTARTSYS.
To request an update of the index data for an index or other object, the
following function should be called: