The patch below does not apply to the 4.16-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 37becec95ac31b209eb1c8e096f1093a7db00f32 Mon Sep 17 00:00:00 2001
From: Omar Sandoval osandov@fb.com Date: Mon, 21 May 2018 17:07:19 -0700 Subject: [PATCH] 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: 312c89fbca06 ("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
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index c67fafaa2fe7..81107ad49f3a 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -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: