log.h really should only include the bare minimum of other headers, as
it is really pulled into pretty much everything else and already in
itself one of the most basic pieces of code we have.
Let's hence drop inclusion of:
1. sd-id128.h because it's entirely unneeded in current log.h
2. errno.h, dito.
3. sys/signalfd.h which we can replace by a simple struct forward
declaration
4. process-util.h which was needed for getpid_cached() which we now hide
in a funciton log_emergency_level() instead, which nicely abstracts
the details away.
5. sys/socket.h which was needed for struct iovec, but a simple struct
forward declaration suffices for that too.
Ultimately this actually makes our source tree larger (since users of
the functionality above must now include it themselves, log.h won't do
that for them), but I think it helps to untangle our web of includes a
tiny bit.
(Background: I'd like to isolate the generic bits of src/basic/ enough
so that we can do a git submodule import into casync for it)
This adds support for a new kernel command line option "systemd.volatile=" that
provides the same functionality that systemd-nspawn's --volatile= switch
provides, but for host systems (i.e. systems booting with a kernel).
It takes the same parameter and has the same effect.
In order to implement systemd.volatile=yes a new service
systemd-volatile-root.service is introduced that only runs in the initrd and
rearranges the root directory as needed to become a tmpfs instance. Note that
systemd.volatile=state is implemented different: it simply generates a
var.mount unit file that is part of the normal boot and has no effect on the
initrd execution.
The way this is implemented ensures that other explicit configuration for /var
can always override the effect of these options. Specifically, the var.mount
unit is generated in the "late" generator directory, so that it only is in
effect if nothing else overrides it.
This moves the VolatileMode enum and its helper functions to src/shared/. This
is useful to then reuse them to implement systemd.volatile= in a later commit.
