[PATCH 1/2] btrfs: Populate btrfs_super_block::log_root_transid

[Qu Wenruo <wqu@suse.com>]

We have btrfs_super_block::log_root_transid to record the transid of log
tree root.

However it's never populated and it's always 0, just as the following
dump-super:
 log_root                30572544
 log_root_transid        0
 log_root_level          0

This patch will populate it with log tree root correctly, so the result
will be:
 log_root                30572544
 log_root_transid        6
 log_root_level          0

This won't affect current kernel behavior or btrfs check result as we
already expect log tree root generation always to be super block
genration + 1.

But it could be later used to detect log tree corruption early.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/transaction.c | 1 +
 fs/btrfs/tree-log.c    | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 3b84f5015029..9d4947079aa3 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -2211,6 +2211,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 
 	btrfs_set_super_log_root(fs_info->super_copy, 0);
 	btrfs_set_super_log_root_level(fs_info->super_copy, 0);
+	btrfs_set_super_log_root_transid(fs_info->super_copy, 0);
 	memcpy(fs_info->super_for_commit, fs_info->super_copy,
 	       sizeof(*fs_info->super_copy));
 
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 1650dc44a5e3..3e16e7b54922 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3131,6 +3131,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 				 log_root_tree->node->start);
 	btrfs_set_super_log_root_level(fs_info->super_for_commit,
 				       btrfs_header_level(log_root_tree->node));
+	btrfs_set_super_log_root_transid(fs_info->super_for_commit,
+				btrfs_header_generation(log_root_tree->node));
 
 	log_root_tree->log_transid++;
 	mutex_unlock(&log_root_tree->log_mutex);
-- 
2.19.0