This also relaxes the inode access modes a bit, in case they were set to
0600: we now set the "r" bit too, i.e. use 0644. This is beneficial
since it permits unpriv code to read the xattrs of the entrypoints
(which require read access). Note that in order to be able to connect()
to a socket inode you need write access, hence this shouldn't compromise
security in any way.
We removed the concept of facts, so we need to update the existing
io.systemd.Basic facts provider to metrics. This commit does just
that. Its mostly mechanical.
This also means that facts.{c,h} and varlink-io.systemd.Facts.{c,h}
are gone now.
The collection of facts is entirely unprivileged and has very little to
do with PID1. PID1 is privileged and single-threaded and a point of
contention, so we shouldn't put things in PID1 that don't need to be
there. A separate service can be enabled/disabled/started/stopped at
will, is easy to sandbox, etc. If it turns out to be necessary to
collect some facts through PID1 in the future, we can always add a
smaller facts endpoint to PID1 again.
