Btrfs: allow empty subvol= again
I got a report that after upgrading to 4.16, someone's filesystems weren't mounting: [ 23.845852] BTRFS info (device loop0): unrecognized mount option 'subvol=' Before 4.16, this mounted the default subvolume. It turns out that this empty "subvol=" is actually an application bug, but it was causing the application to fail, so it's an ABI break if you squint. The generic parsing code we use for mount options (match_token()) doesn't match an empty string as "%s". Previously, setup_root_args() removed the "subvol=" string, but the mount path was cleaned up to not need that. Add a dummy Opt_subvol_empty to fix this. The simple workaround is to use / or . for the value of 'subvol=' . Fixes: 312c89fb ("btrfs: cleanup btrfs_mount() using btrfs_mount_root()") CC: stable@vger.kernel.org # 4.16+ Signed-off-by: Omar Sandoval <osandov@fb.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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