Add support for images with existing partitions and filesystems

Enable support for running vmdb2 with a disk image that has already
been partitioned, with pre-existing filesystems in those partitions.

The kpartx_plugin's new "tags" key takes a list of partition/mountpoint
tags to use when referring to the partitions later in the vmdb2 spec
file.

The mount_plugin has been updated to detect the filesystem and uuid if
the mountpoint tags for the disk image were defined via the new "tags"
kpartx_plugin key, rather than via invoking the mkfs plugin. This allows
the mount_plugin to use the fstype to determine if zerofree can be run
on a partition when it is unmounted during build teardown.

3 files changed, 44 insertions, 5 deletions

diff --git a/vmdb/plugins/kpartx.mdwn b/vmdb/plugins/kpartx.mdwn
index 9bb81a7..0074f38 100644
--- a/vmdb/plugins/kpartx.mdwn
+++ b/vmdb/plugins/kpartx.mdwn
@@ -8,6 +8,17 @@ Step keys:
 
 * `kpartx` — REQUIRED; filename of block device with partitions.
 
+* `tags` — OPTIONAL; list of tags to apply to partitions when re-using
+  an existing image that has already been populated with formatted partitions
+
 Example (in the .vmdb file):
 
+    # typical use
+    - kpartx: "{{ output }}"
+
+    # using an image that already contains partitions containing filesystems
+    # that should be mounted as `/boot` and `/`
     - kpartx: "{{ output }}"
+      tags:
+        - boot
+        - root
diff --git a/vmdb/plugins/kpartx_plugin.py b/vmdb/plugins/kpartx_plugin.py
index baa4f54..2432a16 100644
--- a/vmdb/plugins/kpartx_plugin.py
+++ b/vmdb/plugins/kpartx_plugin.py
@@ -28,14 +28,21 @@ class KpartxPlugin(vmdb.Plugin):
 
 class KpartxStepRunner(vmdb.StepRunnerInterface):
     def get_key_spec(self):
-        return {"kpartx": str}
+        return {"kpartx": str, "tags": []}
 
     def run(self, values, settings, state):
         device = values["kpartx"]
-        tags = state.tags.get_tags()
+        tags = values["tags"]
+        if not tags:
+            tags = state.tags.get_tags()
+        else:
+            # add the tags defined in the plugin spec
+            for tag in tags:
+                state.tags.append(tag)
+
         devs = self.kpartx(device)
         for tag, dev in zip(tags, devs):
-            vmdb.progress("remembering {} as {}".format(dev, tag))
+            vmdb.progress(f"remembering {dev} as {tag}")
             state.tags.set_dev(tag, dev)
 
     def kpartx(self, device):
@@ -78,6 +85,8 @@ class KpartxStepRunner(vmdb.StepRunnerInterface):
             loopdev_info = loopdev_info.pop()
             if loopdev_info["back-file"] is None:
                 continue
-            vmdb.progress("Loop device {} is still bound to back-file {}, "
-                          "removing loop device".format(loop_dev, loopdev_info["back-file"]))
+            vmdb.progress(
+                "Loop device {} is still bound to back-file {}, "
+                "removing loop device".format(loop_dev, loopdev_info["back-file"])
+            )
             vmdb.runcmd(["losetup", "-d", loop_dev])
diff --git a/vmdb/plugins/mount_plugin.py b/vmdb/plugins/mount_plugin.py
index b8ebcb1..30554b7 100644
--- a/vmdb/plugins/mount_plugin.py
+++ b/vmdb/plugins/mount_plugin.py
@@ -76,6 +76,25 @@ class MountStepRunner(vmdb.StepRunnerInterface):
         state.tags.set_builder_mount_point(tag, mount_point, cached=True)
         state.tags.set_target_mount_point(tag, dirname)
 
+        # detect the filesystem and uuid if they are not already known. This
+        # will be the case if the tags were defined via the kpartx plugin,
+        # rather than by the mkfs plugin
+        if not state.tags.get_fstype(tag):
+            fstype = (
+                vmdb.runcmd(["blkid", "-c/dev/null", "-ovalue", "-sTYPE", device])
+                .decode()
+                .strip()
+            )
+            state.tags.set_fstype(tag, fstype)
+            uuid = state.tags.get_fsuuid(tag)
+            if not uuid:
+                uuid = (
+                    vmdb.runcmd(["blkid", "-c/dev/null", "-ovalue", "-sUUID", device])
+                    .decode()
+                    .strip()
+                )
+                state.tags.set_fsuuid(tag, uuid)
+
         return mount_point
 
     def unmount_rootfs(self, values, settings, state):