Add support for updating existing fstab files to writeexts/ssh-rsync

When upgrading (using ssh-rsync) from an existing rawdisk image, there
will already be an fstab. This patch adds support to update the UUID
when a fstab file already exists

2 files changed, 31 insertions, 5 deletions

diff --git a/morphlib/exts/ssh-rsync.write b/morphlib/exts/ssh-rsync.write
index c4577026..81b35a7c 100755
--- a/morphlib/exts/ssh-rsync.write
+++ b/morphlib/exts/ssh-rsync.write
@@ -103,6 +103,13 @@ class SshRsyncWriteExtension(morphlib.writeexts.WriteExtension):
                     location, ['btrfs', 'subvolume', 'delete', new_orig])
             raise
 
+    def fstab_exists(self, temp_root):
+        if (os.path.isfile(os.path.join(temp_root, 'etc', 'fstab'))):
+            temp_fstab = os.path.abspath(os.path.join(temp_root, os.pardir,
+                                         'fstab'))
+            return temp_fstab
+        return None
+
     def populate_remote_orig(self, location, new_orig, temp_root):
         '''Populate the subvolume version_root/orig on location'''
 
@@ -110,6 +117,10 @@ class SshRsyncWriteExtension(morphlib.writeexts.WriteExtension):
         cliapp.runcmd(['rsync', '-as', '--checksum', '--numeric-ids',
                        '--delete', temp_root + os.path.sep,
                        '%s:%s' % (location, new_orig)])
+        if self.fstab_exists(temp_root):
+            cliapp.runcmd(['rsync', '-as', '--checksum', '--numeric-ids',
+                           '--delete', self.fstab_exists(temp_root),
+                           '%s:%s' % (location, new_orig+'/etc/')])
 
     @contextlib.contextmanager
     def _deployed_version(self, location, version_label,
@@ -132,7 +143,11 @@ class SshRsyncWriteExtension(morphlib.writeexts.WriteExtension):
         uuid = cliapp.ssh_runcmd(location, ['blkid', '-s', 'UUID', '-o',
                                  'value', root_disk]).strip()
 
-        self.complete_fstab_for_btrfs_layout(temp_root, uuid)
+        # If we're upgrading from a rawdisk image, there may be an existing
+        # fstab file, we don't want to change that on the image, so create a
+        # temporary directory to store the new file in
+        temp_fstab = self.fstab_exists(temp_root)
+        self.complete_fstab_for_btrfs_layout(temp_root, uuid, temp_fstab)
 
         version_label = os.environ['VERSION_LABEL']
         autostart = self.get_environment_boolean('AUTOSTART')
diff --git a/morphlib/writeexts.py b/morphlib/writeexts.py
index 6ab2dd55..6948f7f5 100644
--- a/morphlib/writeexts.py
+++ b/morphlib/writeexts.py
@@ -74,9 +74,11 @@ class Fstab(object):
 
         self.text += line + '\n'
 
-    def write(self):
+    def write(self, writepath=None):
         '''Rewrite the fstab file to include all new entries.'''
-        with morphlib.savefile.SaveFile(self.filepath, 'w') as f:
+        if writepath is None:
+            writepath = self.filepath
+        with morphlib.savefile.SaveFile(writepath, 'w') as f:
             f.write(self.text)
 
 
@@ -348,7 +350,8 @@ class WriteExtension(cliapp.Application):
             filepath = os.path.join(existing_state_dir, filename)
             cliapp.runcmd(['mv', filepath, subvolume])
 
-    def complete_fstab_for_btrfs_layout(self, system_dir, rootfs_uuid=None):
+    def complete_fstab_for_btrfs_layout(self, system_dir, rootfs_uuid=None,
+                                        temp_fstab=None):
         '''Fill in /etc/fstab entries for the default Btrfs disk layout.
 
         In the future we should move this code out of the write extension and
@@ -368,9 +371,15 @@ class WriteExtension(cliapp.Application):
 
         fstab = Fstab(os.path.join(system_dir, 'etc', 'fstab'))
         existing_mounts = fstab.get_mounts()
+        old_root_device = None
 
         if '/' in existing_mounts:
             root_device = existing_mounts['/']
+            new_root_device = (None if rootfs_uuid is None else
+                              'UUID=%s' % rootfs_uuid)
+            if new_root_device is not None and root_device is not new_root_device:
+                old_root_device = root_device
+                root_device = new_root_device
         else:
             root_device = (self.get_root_device() if rootfs_uuid is None else
                            'UUID=%s' % rootfs_uuid)
@@ -385,7 +394,9 @@ class WriteExtension(cliapp.Application):
                         '%s  /%s  btrfs subvol=%s,defaults,rw,noatime 0 2' %
                         (root_device, state_dir, state_subvol))
 
-        fstab.write()
+        if old_root_device is not None:
+            fstab.text = fstab.text.replace(old_root_device, root_device)
+        fstab.write(temp_fstab)
         return state_dirs_to_create
 
     def find_initramfs(self, temp_root):