linux-mod-manager/lmm/overlayfs.py

from pathlib import Path
import tempfile
from typing import Optional

from lmm.cmd import run_sudo_cmd


def compute_workdirs_location(mount: Path) -> Path:
    with open("/proc/mounts", "r") as f:
        mounts = f.read().split("\n")

    mounted_dirs = [
        m for line in mounts if line != "" and (m := line.strip().split(" ")[1]) != "/"
    ]
    mounted_dirs.sort()

    closest_mount = None
    for m in mounted_dirs:
        if str(mount).startswith(m) and len(m) > len(closest_mount or ""):
            closest_mount = m
            continue

    return Path("/tmp") if closest_mount is None else Path(closest_mount) / ".temp"


class OverlayFSMount:
    upper: Optional[Path]

    lower: list[Path | str]

    workdir: Optional[tempfile.TemporaryDirectory]

    mount_path: Path

    _mounted: bool

    cd: Optional[Path]

    def __init__(
        self,
        upper: Optional[Path],
        lower: list[Path | str],
        mount: Path,
        cd: Optional[Path] = None,
    ):
        self.upper = upper
        self.lower = lower
        self.mount_path = mount
        self._mounted = False
        self.cd = cd

        assert len(lower) < 500, "overlayfs only supports up-to 500 lower directories"

    def create_workdir(self) -> Path:
        # Ensure the temporary directory for workdirs exists
        workdir_location = compute_workdirs_location(self.mount_path)
        if not workdir_location.exists():
            workdir_location.mkdir(parents=True, exist_ok=True)

        # Create the workdir
        self.workdir = tempfile.TemporaryDirectory(
            dir=workdir_location,
        )
        print(f"Temporary workdir {self.workdir.name} created")
        return Path(self.workdir.name)

    def mount(self) -> Optional[Path]:
        lower = ":".join([str(l) for l in self.lower])
        options = f"lowerdir={lower}"
        if self.upper is not None:
            workdir = self.create_workdir()
            options += f",upperdir={self.upper},workdir={workdir}"

        result = run_sudo_cmd(
            [
                "mount",
                "-t",
                "overlay",
                "overlay",
                "-o",
                options,
                str(self.mount_path),
            ],
            cd=self.cd,
        )
        print("Mount result:", result)
        if not result == 0:
            return None

        self._mounted = True
        return self.mount_path

    def unmount(self):
        if self._mounted:
            print("Unmounting...")

            # Remove the mount
            run_sudo_cmd(
                [
                    "umount",
                    str(self.mount_path),
                ]
            )

            # Remove the temporary workdir
            if self.workdir is not None:
                try:
                    # TODO: This fails because the workdir is owned by root
                    self.workdir.cleanup()
                except PermissionError:
                    print(f"Failed to clean temporary directory {self.workdir.name}")

            self._mounted = False

    def __del__(self):
        self.unmount()