[systemd-devel] "primary" Condition for drbd?

[Harald Dunkel]

I missed to mention, drbdadm does know:

	# drbdadm role space
	Primary/Secondary

meaning "space" is primary on this host. You can also look
at /proc/drbd:

	# cat /proc/drbd
	version: 8.4.11 (api:1/proto:86-101)
	srcversion: 19D914EA50F713FCCE48607

	 1: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
	    ns:4044664 nr:0 dw:4044664 dr:726481 al:188 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
	 2: cs:Connected ro:Secondary/Primary ds:UpToDate/UpToDate C r-----
	    ns:0 nr:2228224 dw:2228224 dr:0 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
	 3: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
	    ns:699492 nr:0 dw:699492 dr:266197 al:75 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0

Problem is, it doesn't say "/dev/drbd1". "space" and "1" are
defined in drbd's config files, mapping it to "/dev/drbd1". To
evaluate the condition you have to perform a pretty complex
task.

Does systemd allow to run a program to evaluate a custom
condition in a unit file? Maybe I am too blind to see, but
I haven't found it mentioned on https://www.freedesktop.org/\
software/systemd/man/latest/systemd.unit.html.

The context is: I want to mount/activate /dev/drbd1, if it is
primary. (If it is not, then /dev/drbd1 should be silently
ignored.) Next I want to start the LXC containers provided by
the virtual block device, and setup networking and storage
accordingly. The same should happen for /dev/dbrd{2..n}.

Maybe this is beyond the scope of systemd.


Regards

Harri