btrfs: use the original mount's mount options for the legacy reconfigure

btrfs/330, which tests our old trick to allow

mount -o ro,subvol=/x /dev/sda1 /foo
mount -o rw,subvol=/y /dev/sda1 /bar

fails on the block group tree.  This is because we aren't preserving the
mount options for what is essentially a remount, and thus we're ending
up without the FREE_SPACE_TREE mount option, which triggers our free
space tree delete codepath.  This isn't possible with the block group
tree and thus it falls over.

Fix this by making sure we copy the existing mount options for the
existing fs mount over in this case.

Fixes: f044b318675f ("btrfs: handle the ro->rw transition for mounting different subvolumes")
Reviewed-by: Neal Gompa <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3a677b808f0f75365fead71b438f1783a8ab9f13..f192f8fe0ce62edab4b6a85d2f06a3a08a67ff15 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1451,6 +1451,14 @@ static int btrfs_reconfigure(struct fs_context *fc)
 
        btrfs_info_to_ctx(fs_info, &old_ctx);
 
+       /*
+        * This is our "bind mount" trick, we don't want to allow the user to do
+        * anything other than mount a different ro/rw and a different subvol,
+        * all of the mount options should be maintained.
+        */
+       if (mount_reconfigure)
+               ctx->mount_opt = old_ctx.mount_opt;
+
        sync_filesystem(sb);
        set_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state);