[vfio-users] [iGVT-g] Proper way for systemd service to wait mdev gvt device initialization

[Jordan Glover]

On Sunday, May 19, 2019 6:45 PM, Alex Ivanov <gnidorah at ya.ru> wrote:

> Hello.
> What is the proper way to do that? I have a unit that creates gvt device in the system
>
> ExecStart = "sh -c 'echo a297db4a-f4c2-11e6-90f6-d3b88d6c9525 > /sys/bus/pci/devices/0000:00:02.0/mdev_supported_types/i915-GVTg_V5_8/create'";
> ExecStop = "sh -c 'echo 1 > /sys/bus/pci/devices/0000:00:02.0/a297db4a-f4c2-11e6-90f6-d3b88d6c9525/remove'";
>
> Ideally I would to like to start this service when 0000:00:02.0 device appears in the system, but the problem is that /sys/bus/pci/devices/0000:00:02.0/mdev_supported_types/ tree is populated later, so my service will fail.
>
> So the question what is the proper way to fix that.
>

Use systemd.path helper:
https://www.freedesktop.org/software/systemd/man/systemd.path.html

Examples:
https://blog.andrewkeech.com/posts/170809_path.html

Create gvt.path and gvt.service

gvt.path:
...
[Unit]
Description=gvt path

[Path]
PathExist=/sys/bus/pci/devices/0000:00:02.0/mdev_supported_types

[Install]
WantedBy=multi-user.target


gvt.service:
...
[Unit]
Description=gvt service

[Service]
ExecStart = "sh -c 'echo a297db4a-f4c2-11e6-90f6-d3b88d6c9525 > /sys/bus/pci/devices/0000:00:02.0/mdev_supported_types/i915-GVTg_V5_8/create'"
ExecStop = "sh -c 'echo 1 > /sys/bus/pci/devices/0000:00:02.0/a297db4a-f4c2-11e6-90f6-d3b88d6c9525/remove'"