This patch allows creation of files like
/etc/systemd/system/user-.slice.d/limits.conf with
systemd.units."user-.slice.d/limits.conf" = {
text = ''
[Slice]
CPUAccounting=yes
CPUQuota=50%
'';
};
which previously threw an error
Also renames the systemd-unit-path test to sytsemd-misc, and extends it to
test that `systemd.units` can handle directories. In this case we make
sure that resource limits specified in user slices apply.
