If we remove a directory image (i.e. not a btrfs snapshot) then things might
get quite expensive, hence run this asynchronous in a forked off process, too.
Fall back to a normal copy operation when the backing file system isn't btrfs,
and hence doesn't support cheap snapshotting. Of course, this will be slow, but
given that the execution is asynchronous now, this should be OK.
Fixes: #1308
When recursively copying a directory tree, fix up the file times after having
created all contents in it, so that our changes don't end up altering any of
the directory times.
Let's make sigkill_wait() take a normal pid_t, and add sigkill_waitp() that
takes a pointer (which is useful for usage in _cleanup_), following the usual
logic we have for this.
Cloning an image can be slow, if the image is not on a btrfs subvolume, hence
let's make sure we do this asynchronously in a child process, so that machined
isn't blocked as long as we process the client request.
This adds a new, generic "Operation" object to machined, that is used to track
these kind of background processes.
This is inspired by the MachineOperation object that already exists to make
copy operations asynchronous. A later patch will rework the MachineOperation
logic to use the generic Operation instead.
A downside is that a warning about missing [Install] is printed:
$ systemctl --root=/ enable mnt-test.mount
[/etc/systemd/system/mnt-test.mount:5] Aliases are not allowed for mount units, ignoring.
The unit files have no installation config (WantedBy, RequiredBy, Also, Alias
settings in the [Install] section, and DefaultInstance for template units).
This means they are not meant to be enabled using systemctl.
Possible reasons for having this kind of units are:
1) A unit may be statically enabled by being symlinked from another unit's
.wants/ or .requires/ directory.
2) A unit's purpose may be to act as a helper for some other unit which has
a requirement dependency on it.
3) A unit may be started when needed via activation (socket, path, timer,
D-Bus, udev, scripted systemctl call, ...).
4) In case of template units, the unit is meant to be enabled with some
instance name specified.
That's a bit misleading, but I don't see an easy way to fix this. But
the situation is similar for many other parsing errors, so maybe that's
OK.
The concept of merging units exists so that we can create Unit objects for a
number of names early, and then load them only later, possibly merging units
which then turn out to be symlinked to other names. This of course only makes
sense for unit types where multiple names per unit are supported. For all
others, let's refuse the merge operation early.
We always call one after the other anyway, and this way service_set_socket_fd()
and service_close_socket_fd() nicely match each other as one undoes the effect
of the other.
There's no need to set the no_gc bit for service units that socket units
prepare, as we always keep a proper reference (as maintained by unit_ref_set())
on them, and such references are honoured by the GC logic anyway. Moreover,
explicitly setting the no_gc bit is problematic if the socket gets GC'ed for a
reason, as the service might then leak with the bit set.
In service_set_socket_fd(), let's make sure that if we can't add the requested
dependencies we take no possession of the passed connection fd.
This way, we follow the strict rule: we take possession of the passed fd on
success, but on failure we don't, and the fd remains in possession of the
caller.
