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Commit 37becec9 authored by Omar Sandoval's avatar Omar Sandoval Committed by David Sterba
Browse files

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: default avatarOmar Sandoval <osandov@fb.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent b78e2b78

fs/btrfs/super.c

+3 −0
Original line number Diff line number Diff line
@@ -323,6 +323,7 @@ enum { 
	Opt_ssd, Opt_nossd,

	Opt_ssd_spread, Opt_nossd_spread,

	Opt_subvol,

	Opt_subvol_empty,

	Opt_subvolid,

	Opt_thread_pool,

	Opt_treelog, Opt_notreelog,
@@ -388,6 +389,7 @@ static const match_table_t tokens = { 
	{Opt_ssd_spread, "ssd_spread"},

	{Opt_nossd_spread, "nossd_spread"},

	{Opt_subvol, "subvol=%s"},

	{Opt_subvol_empty, "subvol="},

	{Opt_subvolid, "subvolid=%s"},

	{Opt_thread_pool, "thread_pool=%u"},

	{Opt_treelog, "treelog"},
@@ -461,6 +463,7 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options, 
			btrfs_set_opt(info->mount_opt, DEGRADED);

			break;

		case Opt_subvol:

		case Opt_subvol_empty:

		case Opt_subvolid:

		case Opt_subvolrootid:

		case Opt_device: