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>

2 files changed, 24 insertions, 0 deletions

diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index a9ff9a36b86..7823e9ef995 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -251,6 +251,10 @@ struct fscache_cache_ops {
 	/* unpin an object in the cache */
 	void (*unpin_object)(struct fscache_object *object);
 
+	/* check the consistency between the backing cache and the FS-Cache
+	 * cookie */
+	bool (*check_consistency)(struct fscache_operation *op);
+
 	/* store the updated auxiliary data on an object */
 	void (*update_object)(struct fscache_object *object);
 
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 7a086235da4..d984aff32a1 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -183,6 +183,7 @@ extern struct fscache_cookie *__fscache_acquire_cookie(
 	const struct fscache_cookie_def *,
 	void *);
 extern void __fscache_relinquish_cookie(struct fscache_cookie *, int);
+extern int __fscache_check_consistency(struct fscache_cookie *);
 extern void __fscache_update_cookie(struct fscache_cookie *);
 extern int __fscache_attr_changed(struct fscache_cookie *);
 extern void __fscache_invalidate(struct fscache_cookie *);
@@ -326,6 +327,25 @@ void fscache_relinquish_cookie(struct fscache_cookie *cookie, int retire)
 }
 
 /**
+ * fscache_check_consistency - Request that if the cache is updated
+ * @cookie: The cookie representing the cache object
+ *
+ * Request an consistency check from fscache, which passes the request
+ * to the backing cache.
+ *
+ * Returns 0 if consistent and -ESTALE if inconsistent.  May also
+ * return -ENOMEM and -ERESTARTSYS.
+ */
+static inline
+int fscache_check_consistency(struct fscache_cookie *cookie)
+{
+	if (fscache_cookie_valid(cookie))
+		return __fscache_check_consistency(cookie);
+	else
+		return 0;
+}
+
+/**
  * fscache_update_cookie - Request that a cache object be updated
  * @cookie: The cookie representing the cache object
  *