From f3ec8efbdd4aa4b907a0c9b904d3057639d1b7f8 Mon Sep 17 00:00:00 2001
From: David Lehman <dlehman@redhat.com>
Date: Thu, 21 Aug 2014 12:46:21 -0500
Subject: [PATCH 6/7] Reset default subvolume prior to removing the default
 subvolume.

Resolves: rhbz#1076383
---
 blivet/devicelibs/btrfs.py |  7 +++++++
 blivet/devices.py          | 21 +++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/blivet/devicelibs/btrfs.py b/blivet/devicelibs/btrfs.py
index 0e1171d..94aefaa 100644
--- a/blivet/devicelibs/btrfs.py
+++ b/blivet/devicelibs/btrfs.py
@@ -151,6 +151,13 @@ def get_default_subvolume(mountpoint):
 
     return default
 
+def set_default_subvolume(mountpoint, subvol_id):
+    if not os.path.ismount(mountpoint):
+        raise ValueError("volume not mounted")
+
+    args = ["subvol", "set-default", subvol_id, mountpoint]
+    return btrfs(args)
+
 def create_snapshot(source, dest, ro=False):
     """
         :param str source: path to source subvolume
diff --git a/blivet/devices.py b/blivet/devices.py
index 9df38dd..01a2f62 100644
--- a/blivet/devices.py
+++ b/blivet/devices.py
@@ -5196,6 +5196,23 @@ class BTRFSVolumeDevice(BTRFSDevice, ContainerDevice):
 
         self._defaultSubVolumeID = subvolid
 
+    def _setDefaultSubVolumeID(self, vol_id):
+        """ Set a new default subvolume by id.
+
+            This writes the change to the filesystem, which must be mounted.
+        """
+        try:
+            btrfs.set_default_subvolume(self.originalFormat._mountpoint, vol_id)
+        except BTRFSError as e:
+            log.error("failed to set new default subvolume id (%s): %s",
+                      vol_id, e)
+            # The only time we set a new default subvolume is so we can remove
+            # the current default. If we can't change the default, we won't be
+            # able to remove the subvolume.
+            raise
+        else:
+            self._defaultSubVolumeID = vol_id
+
     @property
     def defaultSubVolume(self):
         default = None
@@ -5355,6 +5372,10 @@ class BTRFSSubVolumeDevice(BTRFSDevice):
     def _destroy(self):
         log_method_call(self, self.name, status=self.status)
         self.volume._do_temp_mount(orig=True)
+        if self.volume._defaultSubVolumeID == self.vol_id:
+            # btrfs does not allow removal of the default subvolume
+            self.volume._setDefaultSubVolumeID(self.volume.vol_id)
+
         mountpoint = self.volume.originalFormat._mountpoint
         if not mountpoint:
             raise RuntimeError("btrfs subvol destroy requires mounted volume")
-- 
1.9.3