debian-forge/devices/org.osbuild.lvm2.lv

#!/usr/bin/python3
"""
Host service for providing access to LVM2 logical volumes

This host service can be used to activate logical volumes
so that they can be accessed from osbuild stages.
The parent volume group is identified via the physical
device which must be passed to this service as parent.

Example usage, where `lvm` here is the lvm partition and
`root` then the logical volume named `root`:
```
"lvm": {
  "type": "org.osbuild.loopback",
  "options": {
  "filename": "disk.img",
  "start": ...,
},
"root": {
  "type": "org.osbuild.lvm2.lv",
  "parent": "lvm",
    "options": {
    "volume": "root"
  }
}
```

Required host tools: lvchange, pvdisplay, lvdisplay
"""

import json
import os
import stat
import subprocess
import sys
import time

from typing import Dict, Tuple

from osbuild import devices


SCHEMA = """
"additionalProperties": false,
"required": ["volume"],
"properties": {
  "volume": {
    "type": "string",
    "description": "Logical volume to active"
  }
}
"""


class LVService(devices.DeviceService):

    def __init__(self, args):
        super().__init__(args)
        self.target = None

    @staticmethod
    def lv_set_active(fullname: str, status: bool):
        mode = "y" if status else "n"
        cmd = [
            "lvchange", "--activate", mode, fullname
        ]
        res = subprocess.run(cmd,
                             check=False,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.STDOUT,
                             encoding="UTF-8")

        if res.returncode != 0:
            data = res.stdout.strip()
            msg = f"Failed to set LV device ({fullname}) status: {data}"
            raise RuntimeError(msg)

    @staticmethod
    def volume_group_for_device(device: str) -> str:
        # Find the volume group that belongs to the device specified via `parent`
        vg_name = None
        count = 0

        cmd = [
            "pvdisplay", "-C", "--noheadings", "-o", "vg_name", device
        ]

        while True:
            res = subprocess.run(cmd,
                                 check=False,
                                 stdout=subprocess.PIPE,
                                 stderr=subprocess.STDOUT,
                                 encoding="UTF-8")

            if res.returncode == 5:
                if count == 10:
                    raise RuntimeError("Could not find parent device")
                time.sleep(1*count)
                count += 1
                continue

            if res.returncode != 0:
                json.dump({"error": res.stdout.strip()}, sys.stdout)
                return 1

            vg_name = res.stdout.strip()
            if vg_name:
                break

        return vg_name

    @staticmethod
    def device_for_logical_volume(vg_name: str, volume: str) -> Tuple[int, int]:
        # Now that we have the volume group, find the specified logical volume and its device path

        cmd = [
            "lvdisplay", "-C", "--noheadings",
            "-o", "lv_kernel_major,lv_kernel_minor",
            "--separator", ";",
            "-S", f"lv_name={volume}",
            vg_name
        ]

        res = subprocess.run(cmd,
                             check=False,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.STDOUT,
                             encoding="UTF-8")

        if res.returncode != 0:
            raise RuntimeError(res.stdout.strip())

        data = res.stdout.strip()
        devnum = list(map(int, data.split(";")))
        assert len(devnum) == 2
        major, minor = devnum[0], devnum[1]

        return major, minor

    def open(self, devpath: str, parent: str, tree: str, options: Dict):
        lv = options["volume"]

        assert not parent.startswith("/")
        parent_path = os.path.join("/dev", parent)

        # Find the volume group that belongs to the device specified
        # via `parent`
        vg = self.volume_group_for_device(parent_path)

        # Activate the logical volume
        self.fullname = f"{vg}/{lv}"
        self.lv_set_active(self.fullname, True)

        # Now that we have the volume group, find the major and minor
        # device numbers for the logical volume
        major, minor = self.device_for_logical_volume(vg, lv)

        # Create the device node for the LV in the build root's /dev
        devname = os.path.join(vg, lv)
        fullpath = os.path.join(devpath, devname)

        os.makedirs(os.path.join(devpath, vg), exist_ok=True)
        os.mknod(fullpath, 0o666 | stat.S_IFBLK, os.makedev(major, minor))

        data = {
            "path": devname,
            "node": {
                "major": major,
                "minor": minor
            },
            "lvm": {
                "vg_name": vg,
                "lv_name": lv
            }
        }
        return data

    def close(self):
        if self.fullname:
            self.lv_set_active(self.fullname, False)
            self.fullname = None


def main():
    service = LVService.from_args(sys.argv[1:])
    service.main()


if __name__ == '__main__':
    r = main()
    sys.exit(r)