FAILED: patch "[PATCH] Btrfs: allow empty subvol= again" failed to apply to 4.16-stable tree

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 <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Omar Sandoval <[email protected]>
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=' .

index c67fafaa2fe7..81107ad49f3a 100644
@@ -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:

Hi Greg,

The attached backported patch should apply to 4.16-stable tree.

The list of enum was later sorted by:
416a72022e43 ("btrfs: sort and group mount option definitions") and so this commit was failing to apply. Backported by putting this new enum at its proper place.

--
Regards
Sudip

From: Omar Sandoval <[email protected]>
Date: Mon, 21 May 2018 17:07:19 -0700
Subject: [PATCH] Btrfs: allow empty subvol= again

commit 37becec95ac31b209eb1c8e096f1093a7db00f32 upstream

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=' .

---
 fs/btrfs/super.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

index 4b817947e00f..8f1e67d0c8c5 100644
@@ -308,8 +308,9 @@ static void btrfs_put_super(struct super_block *sb)
 }
 
 enum {
-	Opt_degraded, Opt_subvol, Opt_subvolid, Opt_device, Opt_nodatasum,
-	Opt_nodatacow, Opt_max_inline, Opt_alloc_start, Opt_nobarrier, Opt_ssd,
+	Opt_degraded, Opt_subvol, Opt_subvol_empty, Opt_subvolid,
+	Opt_device, Opt_nodatasum, Opt_nodatacow, Opt_max_inline,
+	Opt_alloc_start, Opt_nobarrier, Opt_ssd,
 	Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl, Opt_compress,
 	Opt_compress_type, Opt_compress_force, Opt_compress_force_type,
 	Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,

@@ -335,6 +336,7 @@ enum {
 static const match_table_t tokens = {
 	{Opt_degraded, "degraded"},
 	{Opt_subvol, "subvol=%s"},
+	{Opt_subvol_empty, "subvol="},
 	{Opt_subvolid, "subvolid=%s"},
 	{Opt_device, "device=%s"},
 	{Opt_nodatasum, "nodatasum"},

@@ -440,6 +442,7 @@ 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:

2.11.0

4.16 is long end-of-life now, there's nothing I can do for it anymore, sorry. You are responding to an email that is almost a month old :(

greg k-h