[RFC,08/16] bcache: struct cache_sb is only for in-memory super block now

Commit Message

Coly Li July 5, 2020, 3:55 p.m. UTC

We have struct cache_sb_disk for on-disk super block already, it is
unnecessary to keep the in-memory super block format exactly mapping
to the on-disk struct layout.

This patch adds code comments to notice that struct cache_sb is not
exactly mapping to cache_sb_disk anymore, and removes the useless member
csum and pad[5].

Although struct cache_sb does not belong to uapi anymore, but there are
still some on-disk format related macros reference it and it is
unncessary to get rid of such dependency now. So struct cache_sb will
continue to stay in include/uapi/linux/bache.h for now.

Signed-off-by: Coly Li <[e-mail]>
---
 include/uapi/linux/bcache.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Patch

diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
index 561032a070f2..046fa29533a8 100644
--- a/include/uapi/linux/bcache.h
+++ b/include/uapi/linux/bcache.h
@@ -216,8 +216,13 @@  struct cache_sb_disk {
 /*8d0*/
 };
 
+/*
+ * This is for in-memory bcache super block.
+ * NOTE: cache_sb is NOT exactly mapping to cache_sb_disk anymore,
+ *       the member size, ordering and even whole struct size may be
+ *       different from cache_sb_disk now.
+ */
 struct cache_sb {
-	__u64			csum;
 	__u64			offset;	/* sector where this sb was written */
 	__u64			version;
 
@@ -237,8 +242,6 @@  struct cache_sb {
 	__le64			feature_incompat;
 	__le64			feature_ro_compat;
 
-	__u64			pad[5];
-
 	union {
 	struct {
 		/* Cache devices */
@@ -246,7 +249,6 @@  struct cache_sb {
 
 		__u16		block_size;	/* sectors */
 		__u16		bucket_size;	/* sectors */
-
 		__u16		nr_in_set;
 		__u16		nr_this_dev;
 	};