netfs, cachefiles: Add a method to query presence of data in the cache

Add a netfs_cache_ops method by which a network filesystem can ask the
cache about what data it has available and where so that it can make a
multipage read more efficient.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-cachefs@redhat.com
Acked-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Rohith Surabattula <rohiths@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index b46c39d98bbd..614f22213e21 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -244,6 +244,13 @@ struct netfs_cache_ops {
 	int (*prepare_write)(struct netfs_cache_resources *cres,
 			     loff_t *_start, size_t *_len, loff_t i_size,
 			     bool no_space_allocated_yet);
+
+	/* Query the occupancy of the cache in a region, returning where the
+	 * next chunk of data starts and how long it is.
+	 */
+	int (*query_occupancy)(struct netfs_cache_resources *cres,
+			       loff_t start, size_t len, size_t granularity,
+			       loff_t *_data_start, size_t *_data_len);
 };
 
 struct readahead_control;