initrd.target indirection no longer available

[Dimitri John Ledkov <xnox@xxxxxxxxxx>]

Hi,

In v245 systemd started to default to `initrd.target`, instead of
`default.target` in the initrd. However, unlike `default.target` in
the running system, `initrd.target` is not an indirection symlink.

Specifically, default.target is a symlink to like graphical.target or
like multi-user.target and nothing depends on it. Thus one can bake
images that that make default.target to be a symlink to something
else, which can divert boot to a different transaction (reach it,
start a few other transactions) and then isolate to regular
graphical.target/multi-user.target etc.

initrd.target however, is not an indirection symlink, but it s a real
one. So in my case, I do want to subvert initrd boot, reach the
transaction, run a few more transactions, and then start initrd.target
to complete the initrd stage of the boot and pivot to real root.

However it is not trivial to do so, because initrd.target semantics
are those closer to "multi-user.target" or "graphical.target", rather
than default.target (which is strictly only a symlink).

Solution 1 - Would people be open to creating:
1) default-initrd.target which is a symlink to initrd.target
2) changing main.c initrd special target to be default-initrd.target

This way, in the initrd "out of the box" things boot to
default-initrd.target -> initrd.target, but also allow to subvert
default-initrd.target to something else, and later start initrd.target
without modifying any third party that already integrates with
initrd.target (ie. dracut etc).

This also fixes regression from v244, where initrd used to boot to
default.target symlink, and one used to be able to point that symlink
to something else, instead of initrd.target, whilst preserving the
out-of-the-box correct behaviour.

Or in a closer spirit to v244 can we do something like:
Solution 2:
1) if rd.systemd.unit / --unit args passed use those
2) if default.target exists use that
3) else use initrd.target ?

Because v245 has lost sensitivity to
/etc/systemd/system/default.target symlink pointing at something else
but initrd.target.

-- 
Regards,

Dimitri.
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