Btrfs-progs: add command to set default subvol

This introduces a new btrfsctl option, -m, to allow you to set the default'ly
mounted subvolume.  You can do

btrfsctl -m /your/subvolume

and that will make that subvolume the subvolume that is mounted by default, or
you can do

btrfsctl -m <treeid> /any/subvolume

and this will make the subvolume with tree id <treeid> the default'ly mounted
subvolume.  You can get the treeid by using the listing option.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/ioctl.h b/ioctl.h
index b0e5c0db..6a4a2d14 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -126,4 +126,5 @@ struct btrfs_ioctl_ino_lookup_args {
 				   struct btrfs_ioctl_search_args)
 #define BTRFS_IOC_INO_LOOKUP _IOWR(BTRFS_IOCTL_MAGIC, 18, \
 				   struct btrfs_ioctl_ino_lookup_args)
+#define BTRFS_IOC_DEFAULT_SUBVOL _IOW(BTRFS_IOCTL_MAGIC, 19, u64)
 #endif