3 files changed, 226 insertions, 0 deletions
diff --git a/linuxnamespaces/systemd/__init__.py b/linuxnamespaces/systemd/__init__.py
new file mode 100644
index 0000000..d8e7f86
--- /dev/null
+++ b/linuxnamespaces/systemd/__init__.py
@@ -0,0 +1,68 @@
+# Copyright 2024 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: GPL-3
+
+"""Communicate with a systemd instance to create e.g. delegated croups."""
+
+import os
+import sys
+import typing
+
+
+async def start_transient_unit(
+    unitname: str,
+    pids: list[int] | None = None,
+    properties: dict[str, typing.Any] | None = None,
+    dbusdriver: typing.Literal["auto", "jeepney", "dbussy"] = "auto",
+) -> None:
+    """Call the StartTransientUnit dbus method on the user manager."""
+    dbus_properties: list[tuple[str, tuple[str, typing.Any]]] = []
+    if pids is None:
+        pids = [os.getpid()]
+    dbus_properties.append(("PIDs", ("au", pids)))
+    for key, value in ({} if properties is None else properties).items():
+        if isinstance(value, bool):
+            dbus_properties.append((key, ("b", value)))
+        elif isinstance(value, str):
+            dbus_properties.append((key, ("s", value)))
+        else:
+            raise ValueError(
+                f"cannot infer dbus type for property {key} value"
+            )
+    if dbusdriver in ("auto", "jeepney"):
+        try:
+            from .jeepney import start_transient_unit as jeepney_impl
+        except ImportError:
+            pass
+        else:
+            return await jeepney_impl(unitname, dbus_properties)
+    if dbusdriver in ("auto", "dbussy"):
+        try:
+            from .dbussy import start_transient_unit as dbussy_impl
+        except ImportError:
+            pass
+        else:
+            return await dbussy_impl(unitname, dbus_properties)
+    raise NotImplementedError("requested dbusdriver not available")
+
+
+def reexec_as_transient_unit(
+    unitname: str | None = None,
+    properties: dict[str, typing.Any] | None = None,
+    argv: list[str] | None = None,
+) -> typing.NoReturn:
+    """Reexecute the current process via systemd-run thus placing it into a new
+    .scope unit. If no argv is given, sys.argv is used.
+    """
+    execargs = ["systemd-run", "--user", "--scope"]
+    if unitname is not None:
+        execargs.append("--unit=" + unitname)
+    if properties:
+        for key, value in properties.items():
+            if isinstance(value, int):
+                value = str(value)
+            elif not isinstance(value, str):
+                raise ValueError(f"cannot format property {key} value")
+            execargs.append(f"--property={key}={value}")
+    execargs.append("--")
+    execargs.extend(sys.argv if argv is None else argv)
+    os.execvp("systemd-run", execargs)
diff --git a/linuxnamespaces/systemd/dbussy.py b/linuxnamespaces/systemd/dbussy.py
new file mode 100644
index 0000000..77410df
--- /dev/null
+++ b/linuxnamespaces/systemd/dbussy.py
@@ -0,0 +1,81 @@
+# Copyright 2024 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: GPL-3
+
+"""Communicate with a systemd instance via dbus using dbussy."""
+
+import asyncio
+import typing
+
+import ravel
+
+
+class SystemdJobWaiter:
+    """Context manager for waiting for a systemd job to complete.
+    Typical usage:
+
+        with SystemdJobWaiter(bus) as wait:
+            job = create_a_job_on(bus)
+            result = await wait(job)
+    """
+
+    systemd_path = "/org/freedesktop/systemd1"
+    systemd_iface = "org.freedesktop.systemd1.Manager"
+
+    def __init__(self, bus: ravel.Connection):
+        self.bus = bus
+        self.jobs_removed: dict[str, str] = {}
+        self.target_job: str | None = None
+        self.job_done = asyncio.get_running_loop().create_future()
+
+    @ravel.signal(name="JobRemoved", in_signature="uoss")
+    def _on_job_removed(
+        self, _id: int, path: str, _unit: str, result: str
+    ) -> None:
+        if self.target_job is None:
+            self.jobs_removed[path] = result
+        elif self.target_job == path:
+            self.job_done.set_result(result)
+
+    def __enter__(self) -> "SystemdJobWaiter":
+        self.bus.listen_signal(
+            self.systemd_path,
+            False,
+            self.systemd_iface,
+            "JobRemoved",
+            self._on_job_removed,
+        )
+        return self
+
+    async def __call__(self, job: str, timeout: int | float = 60) -> str:
+        assert self.target_job is None
+        self.target_job = job
+        try:
+            return self.jobs_removed[job]
+        except KeyError:
+            return await asyncio.wait_for(self.job_done, timeout)
+
+    def __exit__(self, *exc_info: typing.Any) -> None:
+        self.bus.unlisten_signal(
+            self.systemd_path,
+            False,
+            self.systemd_iface,
+            "JobRemoved",
+            self._on_job_removed,
+        )
+
+
+async def start_transient_unit(
+    unitname: str, properties: list[tuple[str, tuple[str, typing.Any]]]
+) -> None:
+    """Call the StartTransientUnit dbus method on the user manager. The given
+    properties are tuples of property names and dbus-typed values.
+    """
+    bus = await ravel.session_bus_async()
+    with SystemdJobWaiter(bus) as wait:
+        result = await wait(
+            bus["org.freedesktop.systemd1"]["/org/freedesktop/systemd1"]
+            .get_interface("org.freedesktop.systemd1.Manager")
+            .StartTransientUnit(unitname, "fail", properties, [])[0],
+        )
+        if result != "done":
+            raise OSError("StartTransientUnit failed: " + result)
diff --git a/linuxnamespaces/systemd/jeepney.py b/linuxnamespaces/systemd/jeepney.py
new file mode 100644
index 0000000..ef276d3
--- /dev/null
+++ b/linuxnamespaces/systemd/jeepney.py
@@ -0,0 +1,77 @@
+# Copyright 2024 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: GPL-3
+
+"""Communicate with a systemd instance via dbus using jeepney."""
+
+import asyncio
+import contextlib
+import typing
+
+import jeepney.io.asyncio
+
+
+@contextlib.asynccontextmanager
+async def jeepney_listen_signal(
+    router: jeepney.io.asyncio.DBusRouter, matchrule: jeepney.MatchRule,
+) -> jeepney.io.asyncio.FilterHandle:
+    """Call AddMatch/RemoveMatch on context entry/exit and give filtered queue.
+    """
+    jeepney.wrappers.unwrap_msg(
+        await router.send_and_get_reply(
+            jeepney.bus_messages.message_bus.AddMatch(matchrule)
+        ),
+    )
+    try:
+        with router.filter(matchrule) as queue:
+            yield queue
+    finally:
+        jeepney.wrappers.unwrap_msg(
+            await router.send_and_get_reply(
+                jeepney.bus_messages.message_bus.RemoveMatch(matchrule)
+            ),
+        )
+
+
+async def start_transient_unit(
+    unitname: str, properties: list[tuple[str, tuple[str, typing.Any]]]
+) -> None:
+    """Call the StartTransientUnit dbus method on the user manager. The given
+    properties are tuples of property names and dbus-typed values.
+    """
+    async with (
+        jeepney.io.asyncio.open_dbus_router() as router,
+        jeepney_listen_signal(
+            router,
+            jeepney.MatchRule(
+                type="signal",
+                interface="org.freedesktop.systemd1.Manager",
+                member="JobRemoved",
+                path="/org/freedesktop/systemd1",
+            ),
+        ) as queue,
+    ):
+        (scope_job,) = jeepney.wrappers.unwrap_msg(
+            await router.send_and_get_reply(
+                jeepney.new_method_call(
+                    jeepney.DBusAddress(
+                        "/org/freedesktop/systemd1",
+                        bus_name="org.freedesktop.systemd1",
+                        interface="org.freedesktop.systemd1.Manager",
+                    ),
+                    "StartTransientUnit",
+                    "ssa(sv)a(sa(sv))",
+                    (unitname, "fail", properties, []),
+                ),
+            ),
+        )
+        loop = asyncio.get_running_loop()
+        deadline = loop.time() + 60
+        while True:
+            message = jeepney.wrappers.unwrap_msg(
+                await asyncio.wait_for(queue.get(), deadline - loop.time())
+            )
+            if message[1] != scope_job:
+                continue
+            if message[3] != "done":
+                raise OSError("StartTransientUnit failed: " + message[3])
+            return