From: Michael Chang <[email protected]>
Subject: export btrfs_subvol and btrfs_subvolid

We should export btrfs_subvol and btrfs_subvolid to have both visible 
to subsidiary configuration files loaded using configfile. 

Signed-off-by: Michael Chang <[email protected]>

--- a/grub-core/fs/btrfs.c
+++ b/grub-core/fs/btrfs.c
@@ -2931,6 +2931,8 @@
                                subvol_set_env);
   grub_register_variable_hook ("btrfs_subvolid", subvolid_get_env,
                                subvolid_set_env);
+  grub_env_export ("btrfs_subvol");
+  grub_env_export ("btrfs_subvolid");
 }
 
 GRUB_MOD_FINI (btrfs)