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Tobias WaldekranzandJoachim Wiberg
fcc9fe84f4
Add a helper that lets you call a Python function (or lambda) in the
context of a network samespace.
Example:
with infamy.IsolatedMacVlan("eth0") as ns:
res = ns.call(lambda: subprocess.run(["ip", "link"],
capture_output=True))
print(res.stdout, f"\n[exitcode:{res.returncode}]")
The call to subprocess.run will be executed in the context of the
network namespace, and thus only list "lo" and the "iface"
macvlan.
The return value of the function passed to ns.call() is passed back
over a multiprocessing.Pipe, which requires that the object be
"picklable". This is true for most objects (even more complex ones
like the CompletedProcess object seen in the example above). Some
notable exceptions are things like file objects, sockets, etc.
The setns(2) syscall is unfortunately not available in current
versions of Python shipped with neither Ubuntu nor Alpine at the time
of this writing. Therefore, shoot from the hip, assume that we're
running on an x86_64 CPU, and just hotwire the syscall directly with
some constants we found in a dumpster.