3 files changed, 80 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 07d956977a07..1166b15e9bf6 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -373,11 +373,13 @@ struct btrfs_super_block {
  * ones specified below then we will fail to mount
  */
 #define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF    (1ULL << 0)
+#define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL   (2ULL << 0)
 
 #define BTRFS_FEATURE_COMPAT_SUPP               0ULL
 #define BTRFS_FEATURE_COMPAT_RO_SUPP            0ULL
 #define BTRFS_FEATURE_INCOMPAT_SUPP             \
-        BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF
+        (BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF | \
+         BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL)
 
 /*
  * A leaf is full of items. offset and size tell us where to find
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index c6044733198d..7875a75315d0 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1579,6 +1579,79 @@ out:
         return ret;
 }
 
+static long btrfs_ioctl_default_subvol(struct file *file, void __user *argp)
+{
+        struct inode *inode = fdentry(file)->d_inode;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        struct btrfs_root *new_root;
+        struct btrfs_dir_item *di;
+        struct btrfs_trans_handle *trans;
+        struct btrfs_path *path;
+        struct btrfs_key location;
+        struct btrfs_disk_key disk_key;
+        struct btrfs_super_block *disk_super;
+        u64 features;
+        u64 objectid = 0;
+        u64 dir_id;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        if (copy_from_user(&objectid, argp, sizeof(objectid)))
+                return -EFAULT;
+
+        if (!objectid)
+                objectid = root->root_key.objectid;
+
+        location.objectid = objectid;
+        location.type = BTRFS_ROOT_ITEM_KEY;
+        location.offset = (u64)-1;
+
+        new_root = btrfs_read_fs_root_no_name(root->fs_info, &location);
+        if (IS_ERR(new_root))
+                return PTR_ERR(new_root);
+
+        if (btrfs_root_refs(&new_root->root_item) == 0)
+                return -ENOENT;
+
+        path = btrfs_alloc_path();
+        if (!path)
+                return -ENOMEM;
+        path->leave_spinning = 1;
+
+        trans = btrfs_start_transaction(root, 1);
+        if (!trans) {
+                btrfs_free_path(path);
+                return -ENOMEM;
+        }
+
+        dir_id = btrfs_super_root_dir(&root->fs_info->super_copy);
+        di = btrfs_lookup_dir_item(trans, root->fs_info->tree_root, path,
+                                   dir_id, "default", 7, 1);
+        if (!di) {
+                btrfs_free_path(path);
+                btrfs_end_transaction(trans, root);
+                printk(KERN_ERR "Umm, you don't have the default dir item, "
+                       "this isn't going to work\n");
+                return -ENOENT;
+        }
+
+        btrfs_cpu_key_to_disk(&disk_key, &new_root->root_key);
+        btrfs_set_dir_item_key(path->nodes[0], di, &disk_key);
+        btrfs_mark_buffer_dirty(path->nodes[0]);
+        btrfs_free_path(path);
+
+        disk_super = &root->fs_info->super_copy;
+        features = btrfs_super_incompat_flags(disk_super);
+        if (!(features & BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL)) {
+                features |= BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL;
+                btrfs_set_super_incompat_flags(disk_super, features);
+        }
+        btrfs_end_transaction(trans, root);
+
+        return 0;
+}
+
 /*
  * there are many ways the trans_start and trans_end ioctls can lead
  * to deadlocks.  They should only be used by applications that
@@ -1625,6 +1698,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_snap_create(file, argp, 1);
         case BTRFS_IOC_SNAP_DESTROY:
                 return btrfs_ioctl_snap_destroy(file, argp);
+        case BTRFS_IOC_DEFAULT_SUBVOL:
+                return btrfs_ioctl_default_subvol(file, argp);
         case BTRFS_IOC_DEFRAG:
                 return btrfs_ioctl_defrag(file);
         case BTRFS_IOC_RESIZE:
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 79c07b104f91..f1923e0260e3 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -1,3 +1,4 @@
+
 /*
  * Copyright (C) 2007 Oracle.  All rights reserved.
  *
@@ -133,4 +134,5 @@ struct btrfs_ioctl_clone_range_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