qemu-guest-agent not starting

Host environment

• Operating system:
• OS/kernel version:
• Architecture:
• QEMU flavor:
• QEMU version:
• QEMU command line:

systemctl status qemu-guest-agent
● qemu-guest-agent.service - QEMU Guest Agent
     Loaded: loaded (/lib/systemd/system/qemu-guest-agent.service; static; vendor preset: enabled)
     Active: inactive (dead)

déc. 11 13:45:08 mail.jpp.fr systemd[1]: Dependency failed for QEMU Guest Agent.
déc. 11 13:45:08 mail.jpp.fr systemd[1]: qemu-guest-agent.service: Job qemu-guest-agent.service/start failed with result 'dependency'.

Description of problem

Trace found in syslog :

syslog:Dec 11 13:45:08 mail systemd[1]: dev-virtio\x2dports-org.qemu.guest_agent.0.device: Job dev-virtio\x2dports-org.qemu.guest_agent.0.device/start timed out.
syslog:Dec 11 13:45:08 mail systemd[1]: Timed out waiting for device /dev/virtio-ports/org.qemu.guest_agent.0.
syslog:Dec 11 13:45:08 mail systemd[1]: qemu-guest-agent.service: Job qemu-guest-agent.service/start failed with result 'dependency'.
syslog:Dec 11 13:45:08 mail systemd[1]: dev-virtio\x2dports-org.qemu.guest_agent.0.device: Job dev-virtio\x2dports-org.qemu.guest_agent.0.device/start failed with result 'timeout'.

Steps to reproduce

systemctl start qemu-guest-agent

Additional information

Messages when installing the systemd unit :

systemctl enable qemu-guest-agent
Synchronizing state of qemu-guest-agent.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable qemu-guest-agent
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:
• A unit may be statically enabled by being symlinked from another unit's
  .wants/ or .requires/ directory.
• A unit's purpose may be to act as a helper for some other unit which has
  a requirement dependency on it.
• A unit may be started when needed via activation (socket, path, timer,
  D-Bus, udev, scripted systemctl call, ...).
• In case of template units, the unit is meant to be enabled with some
  instance name specified.