Commit 37becec9 authored May 21, 2018 by Omar Sandoval Committed by David Sterba May 28, 2018

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>

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:

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