It if of course related to /proc/cmdline parsing, but is higher-level
functionality built on top of it. It should be in shared/ because it
is something to be used by pid1 and related utilities, not something for
level-level libraries.
v2:
- do not watch mtime of transient and generated dirs
We'd reload the map after every transient unit we created, which we don't
need to do, since we create those units ourselves and know their fragment
path.
This reworks how we load units from disk. Instead of chasing symlinks every
time we are asked to load a unit by name, we slurp all symlinks from disk
and build two hashmaps:
1. from unit name to either alias target, or fragment on disk
(if an alias, we put just the target name in the hashmap, if a fragment
we put an absolute path, so we can distinguish both).
2. from a unit name to all aliases
Reading all this data can be pretty costly (40 ms) on my machine, so we keep it
around for reuse.
The advantage is that we can reliably know what all the aliases of a given unit
are. This means we can reliably load dropins under all names. This fixes#11972.
It turns out most possible symlinks are invalid, because the type has to match,
and template units can only be linked to template units.
I'm not sure if the existing code made the same checks consistently. At least
I don't see the same rules expressed in a single place.
