We need to be able to override the service registered to be run before the guest is shut down by systemd
Just making it a configurable system-wide parameter would be enough

Thanks

+++ This bug was initially created as a clone of Bug #1334982 +++

[...]

In RHEV-M GUI, have options to manage shutdown (and maybe start) options for hosts.

-> Gracefully shutdown all VMs that are running, updating RHEV-M DB
-> Switch to maintenance mode, updating RHEV-M DB

[...]

Other information:

Well, I tried to achieve this by using API calls from the host to RHEV-M. The idea was:

A) systemd service that on shutdown would call the RHEV API to get a list of VMs it has running on it
B) Issue API calls to shutdown all these VMs
C) Put the Host into Maintenance mode
D) Continue shutdown process

Problems:

1) Scopes

My systemd service was always called AFTER the VMs were destroyed, even if it was 'After' vdsmd+libvirt and tons of targets.

This is due to libvirt. When it creates a VM, it tells systemd to assign a scope to it. To make the destruction of the scope dependent on another service, libvirt needs to specifically tell it to systemd. Current implementation is hardcoded in libvirt as 'libvirt-guests.sevice".

So in RHEV, these scopes do not depend on anything, so systemd shuts them down quite early in the shutdown process, killing all the VMs.

[  175.376302] systemd-logind[489]: Power key pressed.
[  175.376312] systemd-logind[489]: Powering Off...
...
[  175.388845] systemd[1]: systemd-machined.service changed running -> stop-sigterm
[  175.388854] systemd[1]: Stopping Virtual Machine and Container Registration Service...
[  175.389604] systemd[1]: machine-qemu\x2d2\x2dCentOS7.scope changed running -> stop-sigterm
[  175.389613] systemd[1]: Stopping Virtual Machine qemu-2-CentOS7.

Looking at libvirt code, it is hard-coded to make this scopes depend only on libvirt-guests.service.

int virSystemdCreateMachine(const char *name, ...
{
....
        if (virDBusCallMethod(conn,
                              NULL,
                              &error,
                              "org.freedesktop.machine1",
                              "/org/freedesktop/machine1",
                              "org.freedesktop.machine1.Manager",
                              "CreateMachineWithNetwork",
                              "sayssusa&ia(sv)",
                              name,
                              16,
                              uuid[0], uuid[1], uuid[2], uuid[3],
                              uuid[4], uuid[5], uuid[6], uuid[7],
                              uuid[8], uuid[9], uuid[10], uuid[11],
                              uuid[12], uuid[13], uuid[14], uuid[15],
                              creatorname,
                              iscontainer ? "container" : "vm",
                              (unsigned int)pidleader,
                              rootdir ? rootdir : "",
                              nnicindexes, nicindexes,
                              3,
                              "Slice", "s", slicename,
                              "After", "as", 1, "libvirtd.service",                  
                              "Before", "as", 1, "libvirt-guests.service") < 0)
...
}

So systemd won't care about my service depending on vdsm because the VMs are assigned to these scopes and not the vdsm service. Result: only the libvirt-guests.service is able to do something here.