From: Christian Brauner <redacted>

Now that we converted btrfs internally to account for idmapped mounts allow the
creation of idmapped mounts on btrfs by setting the FS_ALLOW_IDMAP flag.  We
only need to raise this flag on the btrfs_root_fs_type filesystem since
btrfs_mount_root() is ultimately responsible for allocating the superblock and
is called into from btrfs_mount() associated with btrfs_fs_type.

The conversion of the btrfs inode operations was straightforward. Regarding
btrfs specific ioctls that perform checks based on inode permissions only those
have been allowed that are not filesystem wide operations and hence can be
reasonably charged against a specific mount.

Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Christian Brauner <redacted>
---
/* v2 */
unchanged
---
 fs/btrfs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d07b18b2b250..5ba21f6b443c 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c

@@ -2381,7 +2381,7 @@ static struct file_system_type btrfs_root_fs_type = {
 	.name		= "btrfs",
 	.mount		= btrfs_mount_root,
 	.kill_sb	= btrfs_kill_super,
-	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
+	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA | FS_ALLOW_IDMAP,
 };
 
 MODULE_ALIAS_FS("btrfs");

-- 
2.30.2