[systemd-devel] Start and stop actions of device units

[Zbigniew Jędrzejewski-Szmek]

On Sat, Apr 13, 2013 at 12:30:33PM +0100, Colin Guthrie wrote:
> 'Twas brillig, and Léo Gillot-Lamure at 13/04/13 11:11 did gyre and gimble:
> > Hi.
> > Would it be possible to bind something to the start and stop actions of
> > a device unit ?
> > I've got a device (a hard drive) that I can programmatically plug/unplug
> > using commands such as "echo '0 0 0' > /sys/class/scsi_host/host1/
> > scan"
> > and "echo 1
> >>
> > /sys/devices/pci0000:00/0000:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/delete".
> > The goal is reducing noise.
> > It would be nice to bind these commands in the device unit itself so
> > that other units needing it can start it by themselves, etc.
> 
> So I think this should just be a matter of creating a .service unit with
> appropriate ExecStart/Stop directives and then add a BindTo= directive
> to bind it to the device.

BindTo= would give the opposite ordering than the one required. I
think that RequiredBy=...device, Before=....device,
StopWhenUnneeded=true (in the plug-unplug.unit) should give you what
you need. It might make sense to make the plug-unplug.unit a template,
so that you can enable it for a device by saying 'systemctl enable
plug-unplug at ...device.service'.

Zbyszek