atf_python: Run vnet handlers in $HOME

[markj]

Summary

When kyua runs a test, it creates a temp directory and sets $HOME to
point to it. Tests are run with the cwd set to that temp directory.

When a process attaches to a jail, its cwd is set to the root of the
jail. Modify atf_python to cd to $HOME instead, so that it's easier for
tests to share files.

[zlei]

Looks good to me.

[ngie]

What was the directory at this point in the tests prior to this change?

tests/atf_python/sys/net/vnet.py

8

To support the suggested change below.

360

Using tempfile.gettempdir() is better since it's more explicit.

[markj]

In D54971#1256854, @ngie wrote:

What was the directory at this point in the tests prior to this change?

The root of the jail.

tests/atf_python/sys/net/vnet.py

360

But that's not what I want. It's more useful for vnet handlers to start in the same directory as the main test thread.

[ngie]

tests/atf_python/sys/net/vnet.py

360

The jail module/support in atf_python, etc doesn't maintain the tempdir sandboxing support, even symmetrically between the jails?

[markj]

tests/atf_python/sys/net/vnet.py

360

The test-provided vnet handler invoked below runs in the root of the jail, yes. The vnet.attach() call immediately above is what causes that.

[ngie]

tests/atf_python/sys/net/vnet.py

360

Bummer... that violates POLA for kyua as the default expectation is for kyua put all of the temporary files in temp sandbox directory and to clean everything up when done.