[PATCH v3 1/3] btrfs: add "rescue=usebackuproot" into forced read-only options

According to btrfs(5) man page, all rescue options should require a
read-only mount.

But that read-only check is only introduced for newer rescue options,
not for the pre-existing "usebackuproot" one.

Furthermore, a filesystem that requires "rescue=" mount option already
means it's corrupted, even if "rescue=usebackuproot" allowed the fs to
be mounted RW, one should not trust such fs anymore until a
comprehensive btrfs-check run and proper evaluation.

Change the behavior to match the document, and since
"rescue=usebackuproot" is now a full RO mount option, it is no longer a
one-shot option, therefore remove it from btrfs_clear_oneshot_options().

Signed-off-by: Qu Wenruo <[email protected]>
---
 fs/btrfs/fs.h    | 3 ++-
 fs/btrfs/super.c | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index ab5ed7b4f639..cffb9197a1ab 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -289,7 +289,8 @@ enum {
 	 BTRFS_MOUNT_IGNOREBADROOTS |		\
 	 BTRFS_MOUNT_IGNOREDATACSUMS |		\
 	 BTRFS_MOUNT_IGNOREMETACSUMS |		\
-	 BTRFS_MOUNT_IGNORESUPERFLAGS)
+	 BTRFS_MOUNT_IGNORESUPERFLAGS |		\
+	 BTRFS_MOUNT_USEBACKUPROOT)
 
 /*
  * Compat flags that we support.  If any incompat flags are set other than the
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 0a6ce6c19d8c..e561c8811d6d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -668,7 +668,6 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
  */
 static void btrfs_clear_oneshot_options(struct btrfs_fs_info *fs_info)
 {
-	btrfs_clear_opt(fs_info->mount_opt, USEBACKUPROOT);
 	btrfs_clear_opt(fs_info->mount_opt, CLEAR_CACHE);
 	btrfs_clear_opt(fs_info->mount_opt, NOSPACECACHE);
 }
@@ -692,7 +691,8 @@ bool btrfs_check_options(const struct btrfs_fs_info *info,
 	bool ret = true;
 
 	if (!(flags & SB_RDONLY) &&
-	    (check_ro_option(info, *mount_opt, BTRFS_MOUNT_NOLOGREPLAY, "nologreplay") ||
+	    (check_ro_option(info, *mount_opt, BTRFS_MOUNT_USEBACKUPROOT, "usebackuproot") ||
+	     check_ro_option(info, *mount_opt, BTRFS_MOUNT_NOLOGREPLAY, "nologreplay") ||
 	     check_ro_option(info, *mount_opt, BTRFS_MOUNT_IGNOREBADROOTS, "ignorebadroots") ||
 	     check_ro_option(info, *mount_opt, BTRFS_MOUNT_IGNOREDATACSUMS, "ignoredatacsums") ||
 	     check_ro_option(info, *mount_opt, BTRFS_MOUNT_IGNOREMETACSUMS, "ignoremetacsums") ||
-- 
2.54.0