Move register_machine() and unregister_machine() from
vmspawn-register.{c,h} into shared machine-register.{c,h} so both
nspawn and vmspawn can use the same implementation.
The unified register_machine() uses varlink first (for richer
features like SSH support and unit allocation) with a D-Bus
RegisterMachineWithNetwork fallback for older machined. The
interface adds a class parameter ("vm" or "container") and
local_ifindex for nspawn's network interface support.
The unified unregister_machine() similarly tries varlink first
(io.systemd.Machine.Unregister) before falling back to D-Bus.
Both register_machine() and unregister_machine() only log at debug
level internally, leaving error/notice logging to callers.
Add register_machine_with_fallback() which tries system and/or user
scope registration based on a RuntimeScope parameter
(_RUNTIME_SCOPE_INVALID for both), and
unregister_machine_with_fallback() as its counterpart. Both use
RET_GATHER() to collect errors from each scope.
Make --register= a tristate (yes/no/auto) defaulting to auto. When
set to auto, registration failures are logged at notice level and
ignored. When set to yes, failures are fatal.
Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>
Daan De Meyer
1e084aad7d