This makes sense from the point of view of the whole distribution:
if there are some specific files that have syntax problems, or unknown
users or groups, or use unsupported features, failing the whole service
is not useful.
In particular, services with tmpfiles --boot should not be started after boot.
The premise of --boot is that there are actions which are only safe to do once
during boot, because the state evolves later through other means and re-running
the boot-time setup would destroy it. If services with --boot fail in the
initial transaction, they would be re-run later on when a unit which
(indirectly) depends on them is started, causing problems.
Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1507501.
(If we had a mode where a service would at most run once, and would not be
started in subsequent transactions, that'd be a good additional safeguard.
Using ExecStart=-... is a bit like that, but it causes all failure to be
ignored, which is too big of a hammer.)
npsawn containers generally have CAP_MKNOD, since this is required
to make PrviateDevices= work. Thus, it's not useful anymore to
conditionalize the kmod static device node units.
Use CAP_SYS_MODULES instead which is not available for nspawn
containers. However, the static device node logic is only done for being
able to autoload modules with it, and if we can't do that there's no
point in doing it.
Without this, tmpfiles-setpu-dev would be re-run if any other service,
which pulls in basic.target, was started after setup-dev was finished
and before basic.target was active.
As of kmod v14, it is possible to export the static node information from
/lib/modules/`uname -r`/modules.devname in tmpfiles.d(5) format.
Use this functionality to let systemd-tmpfilesd create the static device nodes
at boot, and drop the functionality from systemd-udevd.
As an effect of this we can move from systemd-udevd to systemd-tmpfiles-setup-dev:
* the conditional CAP_MKNOD (replaced by checking if /sys is mounted rw)
* ordering before local-fs-pre.target (see 89d09e1b5c)
