[PATCH] btrfs: Deprecate unused super block member, log_root_transid

[Qu Wenruo]

The member log_root_transid is never used.
It's always kept untouched even when updating log tree root.

And populating it without introducing new incompat flags could easily
cause back-compatibility problems.
So just mark it unused.

Signed-off-by: Qu Wenruo <w...@suse.com>
---
 fs/btrfs/ctree.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 53af9f5253f4..9adc53db679a 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -214,8 +214,8 @@ struct btrfs_super_block {
        __le64 chunk_root;
        __le64 log_root;
 
-       /* this will help find the new super based on the log root */
-       __le64 log_root_transid;
+       /* This member is never touched, should always be 0 */
+       __le64 __unused_log_root_transid;
        __le64 total_bytes;
        __le64 bytes_used;
        __le64 root_dir_objectid;
@@ -2317,8 +2317,6 @@ BTRFS_SETGET_STACK_FUNCS(super_chunk_root_level, struct 
btrfs_super_block,
                         chunk_root_level, 8);
 BTRFS_SETGET_STACK_FUNCS(super_log_root, struct btrfs_super_block,
                         log_root, 64);
-BTRFS_SETGET_STACK_FUNCS(super_log_root_transid, struct btrfs_super_block,
-                        log_root_transid, 64);
 BTRFS_SETGET_STACK_FUNCS(super_log_root_level, struct btrfs_super_block,
                         log_root_level, 8);
 BTRFS_SETGET_STACK_FUNCS(super_total_bytes, struct btrfs_super_block,
-- 
2.19.1