Use overlayfs when deploying

When deploying, configuration extensions are run against the unpacked
tarball of a system created by a build. If we are to use OSTree to
store systems (rather than tarballs) this will not be possible as the
result of `ostree checkout` would be read-only.

To solve this, we use overlayfs to mount the unpacked tarball
underneath a temporary directory somewhere, and run the configuration
extensions on that mount point. This means that the changes are
made in the temporary directory rather than directly on the tarball.

1 files changed, 34 insertions, 4 deletions

diff --git a/morphlib/plugins/deploy_plugin.py b/morphlib/plugins/deploy_plugin.py
index 63cc4688..576b007c 100644
--- a/morphlib/plugins/deploy_plugin.py
+++ b/morphlib/plugins/deploy_plugin.py
@@ -439,6 +439,8 @@ class DeployPlugin(cliapp.Plugin):
         system_status_prefix = '%s[%s]' % (old_status_prefix, system['morph'])
         self.app.status_prefix = system_status_prefix
         try:
+            system_tree = None
+
             # Find the artifact to build
             morph = morphlib.util.sanitise_morphology_path(system['morph'])
             srcpool = build_command.create_source_pool(build_repo, ref, morph)
@@ -502,6 +504,9 @@ class DeployPlugin(cliapp.Plugin):
                                              system_tree, deploy_location)
                 finally:
                     self.app.status_prefix = system_status_prefix
+                    if system_tree and os.path.exists(system_tree):
+                        morphlib.fsutils.unmount(self.app.runcmd, system_tree)
+                        shutil.rmtree(system_tree)
         finally:
             self.app.status_prefix = old_status_prefix
 
@@ -539,9 +544,22 @@ class DeployPlugin(cliapp.Plugin):
                      artifact, deployment_type, location, env):
         # deployment_type, location and env are only used for saving metadata
 
-        # Create a tempdir to extract the rootfs in
-        system_tree = tempfile.mkdtemp(dir=deploy_tempdir)
+        deployment_dir = tempfile.mkdtemp(dir=deploy_tempdir)
 
+        # Create a tempdir to extract the rootfs in
+        system_tree = tempfile.mkdtemp(dir=deployment_dir)
+
+        # Create temporary directory for overlayfs
+        overlay_dir = os.path.join(deployment_dir,
+                                   '%s-upperdir' % artifact.name)
+        if not os.path.exists(overlay_dir):
+            os.makedirs(overlay_dir)
+        work_dir = os.path.join(deployment_dir, '%s-workdir' % artifact.name)
+        if not os.path.exists(work_dir):
+            os.makedirs(work_dir)
+
+        deploy_tree = os.path.join(deployment_dir,
+                                   'overlay-deploy-%s' % artifact.name)
         try:
             # Unpack the artifact (tarball) to a temporary directory.
             self.app.status(msg='Unpacking system for configuration')
@@ -563,18 +581,30 @@ class DeployPlugin(cliapp.Plugin):
                 msg='System unpacked at %(system_tree)s',
                 system_tree=system_tree)
 
+            options = '-olowerdir=%s,upperdir=%s,workdir=%s' % \
+                (system_tree, overlay_dir, work_dir)
+            morphlib.fsutils.mount(self.app.runcmd,
+                                   'overlay-deploy-%s' % artifact.name,
+                                   deploy_tree, fstype='overlay',
+                                   options=options)
+
             self.app.status(
                 msg='Writing deployment metadata file')
             metadata = self.create_metadata(
                     artifact, root_repo_dir, deployment_type, location, env)
             metadata_path = os.path.join(
-                    system_tree, 'baserock', 'deployment.meta')
+                    deploy_tree, 'baserock', 'deployment.meta')
             with morphlib.savefile.SaveFile(metadata_path, 'w') as f:
                 json.dump(metadata, f, indent=4,
                           sort_keys=True, encoding='unicode-escape')
-            return system_tree
+            return deploy_tree
         except Exception:
             shutil.rmtree(system_tree)
+            shutil.rmtree(overlay_dir)
+            shutil.rmtree(work_dir)
+            if deploy_tree and os.path.exists(deploy_tree):
+                morphlib.fsutils.unmount(self.app.runcmd, deploy_tree)
+                shutil.rmtree(deploy_tree)
             raise
 
     def run_deploy_commands(self, deploy_tempdir, env, artifact, root_repo_dir,