devices: add detectpv option to lvm2.lv to auto-discover PV

This is needed for bootc where all mounts need to be from the
same physical disk/loop so that bootupd works. The idea is
that in the manifest the new option `detectv` is added and
the parent device is the full disk instead of the PV partition
that is currently used and that results in multiple loop devices
for each partition.

So a manifest now looks like:
```json
"devices": {
  "disk": {
    "type": "org.osbuild.loopback",
    "options": {
      "filename": "disk.raw",
      "partscan": true
    }
  },
  "rootlv": {
    "type": "org.osbuild.lvm2.lv",
    "parent": "disk",
    "options": {
      "volume": "rootlv",
      "detectpv": true
    }
  }
},
```
instead of the alternative way via the partition (like this):
```json
"devices": {
  "device": {
    "type": "org.osbuild.lvm2.lv",
    "parent": "rootvg",
    "options": {
      "volume": "rootlv"
    }
  },
  "rootvg": {
    "type": "org.osbuild.loopback",
    "options": {
      "filename": "disk.raw",
      "start": 3127296,
      "size": 17844191,
      "lock": true
    }
  }
}
```

The approach via `detectpv` means that it is impossible to put two
identically named logical volume in two different volume groups
on the same "physical" disk (loop-device).

If this is a problem we need a different approach, we could create
the `vg_name` in `org.osbuild.lvm2.create` in a predicatable but
non-clashing way, e.g. it could be a `{filename}-{start}-{size}`
and we would add the name to `org.osbuild.lvm2.lv` in options.
This would still mean that we cannot do two LVM builds in parallel
on the same host with identical `{filename}-{start}-{size}` so
also not an ideal solution. Or we just put a random vg_name in
the manifest but that also means no parallel image builds for
the same manifest on the same host.

devices/org.osbuild.lvm2.lv

@@ -44,6 +44,11 @@ SCHEMA = """
   "volume": {
     "type": "string",
     "description": "Logical volume to active"
+  },
+  "detectpv": {
+    "type": "boolean",
+    "default": false,
+    "description": "Detect the PV for the LV automatically on the given device"
   }
 }
 """
@@ -105,6 +110,21 @@ class LVService(devices.DeviceService):
             msg = f"Failed to set LV device ({fullname}) status: {data}"
             raise RuntimeError(msg)
 
+    def auto_detect_volume_group(self, device, lv_name: str) -> str:
+        lvs_output = subprocess.check_output(["lvs", "--reportformat=json"])
+        for lv in json.loads(lvs_output)["report"][0]["lv"]:
+            if lv["lv_name"] == lv_name:
+                vg_name = lv["vg_name"]
+                # cross check that is comes from the expected device
+                pvs_output = subprocess.check_output(["pvs", "--reportformat=json"])
+                for pv in json.loads(pvs_output)["report"][0]["pv"]:
+                    if pv["vg_name"] == vg_name:
+                        if not pv["pv_name"].startswith(device):
+                            print(f"WARNING: ignoring {pv['pv_name']} because it is not on {device}", file=sys.stderr)
+                        else:
+                            return vg_name
+        raise RuntimeError(f"cannot find {lv_name} on {device}")
+
     def volume_group_for_device(self, device: str) -> Union[int, str]:
         # Find the volume group that belongs to the device specified via `parent`
         vg_name = None
@@ -126,7 +146,7 @@ class LVService(devices.DeviceService):
 
             if res.returncode == 5:
                 if count == 10:
-                    raise RuntimeError("Could not find parent device")
+                    raise RuntimeError(f"Could not find parent device")
                 time.sleep(1 * count)
                 count += 1
                 continue
@@ -173,6 +193,7 @@ class LVService(devices.DeviceService):
 
     def open(self, devpath: str, parent: str, tree: str, options: Dict):
         lv = options["volume"]
+        detectpv = options.get("detectpv", False)
 
         assert not parent.startswith("/")
         parent_path = os.path.join("/dev", parent)
@@ -182,7 +203,18 @@ class LVService(devices.DeviceService):
 
         # Find the volume group that belongs to the device specified
         # via `parent`
-        vg = self.volume_group_for_device(parent_path)
+        #
+        # In theory "detectpv" could be the default - but that would
+        # change how old manifests work which is risky so only use it
+        # for on newer manifests for now
+        if detectpv:
+            # "new" way to detct vg_name: device can be the full disk/loop that
+            # contains the PV
+            vg = self.auto_detect_volume_group(parent_path, lv)
+        else:
+            # "old" style of detecting the vg_name, needs the pv partition
+            # in parent_path
+            vg = self.volume_group_for_device(parent_path)
 
         # Activate the logical volume
         self.fullname = f"{vg}/{lv}"

devices/test/test_lv.py

@@ -0,0 +1,60 @@
+#!/usr/bin/python3
+
+import pytest
+
+DEVICES_NAME = "org.osbuild.lvm2.lv"
+
+mocked_lvs_output = """
+{
+    "report": [
+        {
+            "lv": [
+                {"lv_name":"rootlv", "vg_name":"1d2b2150-8de2-4b68-b387-f9bc709190e8", "lv_attr":"-wi-------", "lv_size":"3.86g", "pool_lv":"", "origin":"", "data_percent":"", "metadata_percent":"", "move_pv":"", "mirror_log":"", "copy_percent":"", "convert_lv":""}
+            ]
+        }
+    ]
+}
+"""
+
+mocked_pvs_output = """
+{
+       "report": [
+           {
+               "pv": [
+                   {"pv_name":"/dev/loop1p4", "vg_name":"1d2b2150-8de2-4b68-b387-f9bc709190e8", "pv_fmt":"lvm2", "pv_attr":"a--", "pv_size":"8.50g", "pv_free":"4.64g"}
+               ]
+           }
+       ]
+   }
+
+"""
+
+
+def mocked_check_output(args):
+    if args[0] == "lvs":
+        return mocked_lvs_output
+    if args[0] == "pvs":
+        return mocked_pvs_output
+    pytest.fail(f"unexpected arg {args}")
+    return ""
+
+
+def test_lvm2_lv_auto_detect_volume_group_happy(monkeypatch, devices_service):
+    monkeypatch.setattr("subprocess.check_output", mocked_check_output)
+    vg_name = devices_service.auto_detect_volume_group("/dev/loop1", "rootlv")
+    assert vg_name == "1d2b2150-8de2-4b68-b387-f9bc709190e8"
+
+
+def test_lvm2_lv_auto_detect_volume_group_lv_not_found(monkeypatch, devices_service):
+    monkeypatch.setattr("subprocess.check_output", mocked_check_output)
+    with pytest.raises(RuntimeError) as exc:
+        devices_service.auto_detect_volume_group("/dev/loop1", "other-lv")
+    assert str(exc.value) == "cannot find other-lv on /dev/loop1"
+
+
+def test_lvm2_lv_auto_detect_volume_group_wrong_device(monkeypatch, capfd, devices_service):
+    monkeypatch.setattr("subprocess.check_output", mocked_check_output)
+    with pytest.raises(RuntimeError) as exc:
+        devices_service.auto_detect_volume_group("/dev/other/loop", "rootlv")
+    assert str(exc.value) == "cannot find rootlv on /dev/other/loop"
+    assert capfd.readouterr().err == "WARNING: ignoring /dev/loop1p4 because it is not on /dev/other/loop\n"