This pulls out the hwdb managment from udevadm into an independent tool.
The old code is left in place for backwards compatibility, and easy of
testing, but all documentation is dropped to encourage use of the new
tool instead.
In some cases it is preferable to ship system images with a pre-generated
binary hwdb database, to avoid having to build it at runtime, avoid shipping
the source hwdb files, or avoid storing large binary files in /etc.
So if hwdb.bin does not exist in /etc/udev/, fall back to looking for it in
UDEVLIBEXECDIR. This keeps the possibility to add files to /etc/udev/hwdb.d/
and re-generating the database which trumps the one in /usr/lib.
Add a new --usr flag to "udevadm hwdb --update" which puts the database
into UDEVLIBEXECDIR.
Adjust systemd-udev-hwdb-update.service to not generate the file in /etc if we
already have it in /usr.
The only update service we really need to guard like this is
systemd-tmpfiles-setup.service since if invoked manually might create
/var/run/nologin and thus blocking the user from login. The other
services are pretty much idempotent and don't suffer by this problem,
hence let's simplify them.
Tom Gundersen