[linux-lvm] clvmd interface question

[Patrick Caulfield]

John DeFranco wrote:
> Hi, I'm looking for some information. I'm interested in learning more
> about the clvmd daemon. I've search and found various pieces of info in
> addition to looking at the code. Specifically I looking to for
> information (a spec) on how one might be able to add a new cluster
> manager plugin if you will (if that is even possible). I know that clvmd
> interfaces with a couple of different cluster managers now but I'd like
> to expland this if possible.

clvmd supports cman and gulm, it has it's own internal function switch that
determines what to do for each cluster manager.

To be honest it's not a good API as it was originally only designed to work with
cman and the gulm support was bolted on later - so adding a new cluster manager
might be a bit of work.

Have a look at the bottom of LVM2/daemons/clvmd/clvmd-cman for the function switch.

You'll also need to be aware that CMAN provides its own messaging system, which
gulm does not. If your cluster manager provides a messaging system then I
recommend you use it - otherwise you should be able to use the tcp-comms.c file
with clvmd (that gulm support uses).

Another way, that might be easier, is to patch clvmd with the libcman patch in
head of cluster CVS (cluster/cman/lib/clvmd-libcman.diff) and write a library
for your cluster manager that emulates libcman - that one is a nice simple API
and it will be supported by future versions of cman too.

-- 

patrick