(cherry picked from commit e6627f2)

Related: #2156620

…dden by more specific dropins

(cherry picked from commit f5dd6e5)

Related: #2156620

This is what upstream commit cc5549c
has done, but just for a single shell file.

RHEL-only

Related: #2156620

We would miss anything created under a template instance.

(cherry picked from commit 4e2ac45)

Related: #2156620

to avoid possible word splitting.

[dtardon: Dropped changes to other files.]

(cherry picked from commit 3882526)

Related: #2156620

Bash will generate a very nice message for us:
/tmp/ff.sh: line 1: SOMEVAR: parameter null or not set

Let's save some keystrokes by not replacing this with our own inferior
messages.

[dtardon: Dropped changes to other files.]

(cherry picked from commit d7ff524)

Related: #2156620

Not not IN_SET(…) is just too much for my poor brain. Let's invert
the expression to make it easier to undertand.

(cherry picked from commit b146a7345b69de16e88347acadb3783ffeeaad9d)

Related: #2156620

In containers/podman#16107, starting of a transient
slice unit fails because there's a "global" drop-in
/usr/lib/systemd/user/slice.d/10-oomd-per-slice-defaults.conf (provided by
systemd-oomd-defaults package to install some default oomd policy). This means
that the unit_is_pristine() check fails and starting of the unit is forbidden.

It seems pretty clear to me that dropins at any other level then the unit
should be ignored in this check: we now have multiple layers of drop-ins
(for each level of the cgroup path, and also "global" ones for a specific
unit type). If we install a "global" drop-in, we wouldn't be able to start
any transient units of that type, which seems undesired.

In principle we could reject dropins at the unit level, but I don't think that
is useful. The whole reason for drop-ins is that they are "add ons", and there
isn't any particular reason to disallow them for transient units. It would also
make things harder to implement and describe: one place for drop-ins is good,
but another is bad. (And as a corner case: for instanciated units, a drop-in
in the template would be acceptable, but a instance-specific drop-in bad?)

Thus, $subject.

While at it, adjust the message. All the conditions in unit_is_pristine()
essentially mean that it wasn't loaded (e.g. it might be in an error state),
and that it doesn't have a fragment path (now that drop-ins are acceptable).
If there's a job for it, it necessarilly must have been loaded. If it is
merged into another unit, it also was loaded and found to be an alias.
Based on the discussion in the bugs, it seems that the current message
is far from obvious ;)

Fixes containers/podman#16107,
https://bugzilla.redhat.com/show_bug.cgi?id=2133792.

(cherry picked from commit 1f83244641f13a9cb28fdac7e3c17c5446242dfb)

Resolves: #2156620

clear_services() is renamed to clear_units() and now takes a full
unit name including the suffix as an argument.

_clear_service() is renamed to clear_unit() and changed likewise.
create_service() didn't have the same underscore prefix, and I don't think
it's useful or needed for a local function, so it is removed.

No functional change.

(cherry picked from commit 5731e1378ad6256e34f3da33ee993343f025c075)

Related: #2156620

Slices are worth testing too, because they don't need a fragment path so they
behave slightly differently than service units. I'm making this a separate
patch from the actual tests that I wanted to add later because it's complex
enough on its own.

(cherry picked from commit f80c874af376052b6b81f47cbbc43d7fecd98cd6)

Related: #2156620

We want to test four things:
- that the transient units are successfully started when drop-ins exist
- that the transient setings override the defaults
- the drop-ins override the transient settings (the same as for a normal unit)
- that things are the same before and after a reload

To make things more fun, we start and stop units in two different ways: via
systemctl and via a direct busctl invocation. This gives us a bit more coverage
of different code paths.

(cherry picked from commit 6854434cfb5dda10c07d95835c38b75e5e71c2b5)

Related: #2156620

(cherry picked from commit c3fa408dcc03bb6dbd11f180540fb9e684893c39)

Related: #2156620