[PATCH 2/2] btrfs: rescue/zero-log: Manually write all supers to handle extent tree error more gracefully

[Qu Wenruo <wqu@suse.com>]

[BUG]
Even "btrfs rescue zero-log" only reset btrfs_super_block::log_root and
btrfs_super_block::log_root_level, we still use trasction to write all
super blocks for all devices.

This means we can't handle things like corrupted extent tree:

  checksum verify failed on 2172747776 found 000000B6 wanted 00000000
  checksum verify failed on 2172747776 found 000000B6 wanted 00000000
  bad tree block 2172747776, bytenr mismatch, want=2172747776, have=0
  WARNING: could not setup extent tree, skipping it
  Clearing log on /dev/nvme/btrfs, previous log_root 0, level 0
  ERROR: Corrupted fs, no valid METADATA block group found
  ERROR: attempt to start transaction over already running one

[CAUSE]
Because we have extra check in transaction code to ensure we have valid
METADATA block groups.

In fact we don't really need transaction at all.

[FIX]
Instead of commit transaction, we can just call write_all_supers()
manually, so we can still handle multi-device fs while avoid above
error.

Also, add OPEN_CTREE_NO_BLOCK_GROUPS open ctree flag to make it more
robust.

Reported-by: Christian Pernegger <pernegger@gmail.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 cmds/rescue.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/cmds/rescue.c b/cmds/rescue.c
index e8eab6808bc3..087c33befeff 100644
--- a/cmds/rescue.c
+++ b/cmds/rescue.c
@@ -165,7 +165,6 @@ static int cmd_rescue_zero_log(const struct cmd_struct *cmd,
 			       int argc, char **argv)
 {
 	struct btrfs_root *root;
-	struct btrfs_trans_handle *trans;
 	struct btrfs_super_block *sb;
 	char *devname;
 	int ret;
@@ -187,7 +186,8 @@ static int cmd_rescue_zero_log(const struct cmd_struct *cmd,
 		goto out;
 	}
 
-	root = open_ctree(devname, 0, OPEN_CTREE_WRITES | OPEN_CTREE_PARTIAL);
+	root = open_ctree(devname, 0, OPEN_CTREE_WRITES | OPEN_CTREE_PARTIAL |
+			  OPEN_CTREE_NO_BLOCK_GROUPS);
 	if (!root) {
 		error("could not open ctree");
 		return 1;
@@ -198,13 +198,14 @@ static int cmd_rescue_zero_log(const struct cmd_struct *cmd,
 			devname,
 			(unsigned long long)btrfs_super_log_root(sb),
 			(unsigned)btrfs_super_log_root_level(sb));
-	trans = btrfs_start_transaction(root, 1);
-	BUG_ON(IS_ERR(trans));
 	btrfs_set_super_log_root(sb, 0);
 	btrfs_set_super_log_root_level(sb, 0);
-	btrfs_commit_transaction(trans, root);
+	ret = write_all_supers(root->fs_info);
+	if (ret < 0) {
+		errno = -ret;
+		error("failed to write dev supers: %m");
+	}
 	close_ctree(root);
-
 out:
 	return !!ret;
 }
-- 
2.24.0