lvscan_plugin: support for existing images with logical volumes

The lvscan_plugin is used to detect logical volumes in existing disk
images. The volumes are tagged by the plugin, enabling them to be
mounted.

2 files changed, 97 insertions, 0 deletions

diff --git a/vmdb/plugins/lvscan.mdwn b/vmdb/plugins/lvscan.mdwn
new file mode 100644
index 0000000..ff4304c
--- /dev/null
+++ b/vmdb/plugins/lvscan.mdwn
@@ -0,0 +1,23 @@
+Step: lvscan
+-----------------------------------------------------------------------------
+
+Scans for existing LVM2 logical volumes (LVs) within a named volume group.
+This is useful when using an existing image as input which has been
+pre-populated with LVM logical volumes, allowing the volumes to be mounted.
+
+Step keys:
+
+* `lvscan` — REQUIRED; value is the name of the volume group containing
+  the logical volumes.
+
+* `tags` — REQUIRED; list of tags to apply to the discovered logical
+  volumes. The tags must match names of volumes in the volume group. Volumes
+  in the image which do not need to be mounted can be omitted from the tags
+  list
+
+Example (in the .vmdb file):
+
+    - lvscan: the_volume_group
+      tags:
+        - lv_one
+        - lv_two
diff --git a/vmdb/plugins/lvscan_plugin.py b/vmdb/plugins/lvscan_plugin.py
new file mode 100644
index 0000000..08bf31d
--- /dev/null
+++ b/vmdb/plugins/lvscan_plugin.py
@@ -0,0 +1,74 @@
+# Copyright 2023  Andy Piper
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# =*= License: GPL-3+ =*=
+
+import json
+
+import vmdb
+
+
+class LvscanPlugin(vmdb.Plugin):
+    def enable(self):
+        self.app.step_runners.add(LvscanStepRunner())
+
+
+class LvscanStepRunner(vmdb.StepRunnerInterface):
+    def get_key_spec(self):
+        return {"lvscan": str, "tags": []}
+
+    def run(self, values, settings, state):
+        for v in get_logical_volumes(values):
+            dev = v["lv_path"]
+            tag = v["lv_name"]
+            vmdb.progress(f"remembering {dev} as {tag}")
+            state.tags.append(tag)
+            state.tags.set_dev(tag, dev)
+            vmdb.runcmd(["lvchange", "-a", "y", dev])
+
+    def teardown(self, values, settings, state):
+        vgname = values["lvscan"]
+        vmdb.runcmd(["vgchange", "-an", vgname])
+
+
+def get_logical_volumes(values):
+    vgname = values["lvscan"]
+    tags = values["tags"]
+    vmdb.runcmd(["lvscan"])
+    volumes = json.loads(
+        vmdb.runcmd(
+            [
+                "lvdisplay",
+                "-C",
+                "-o",
+                "lv_name,vg_name,lv_path",
+                "--report-format",
+                "json",
+            ]
+        )
+    )["report"][0]["lv"]
+
+    # ensure all tags have a corresponding volume, but not all volumes need
+    # a matching tag
+    matched_vols = [
+        v for v in volumes if v["lv_name"] in tags and v["vg_name"] == vgname
+    ]
+    if len(matched_vols) < len(tags):
+        matched_tags = [v["lv_name"] for v in matched_vols]
+        unmatched_tags = sorted(set(tags).difference(matched_tags))
+        raise RuntimeError(
+            f'unmatched tags in volume group "{vgname}": {unmatched_tags}'
+        )
+    return matched_vols