[Linux-cluster] CMAN and qdiskd (limited?) online reconfig capabilities

[Patrick Caulfield]

Pena, Francisco Javier wrote:
> Hello everyone,
> 
> While checking some strange cman startup behavior (it always assigns 1 vote to each cluster node, no matter what I set in the cluster.conf file), I have spent some time digging through the cluster code to understand how it manages online reconfigurations.

I think that's a bug introduced in U4 - it's fixed in U5.

> In the Red Hat docs (and also at the RH436 course) we are told that the following command sequence is required to update the cluster config:
> 
> - ccs_tool update /etc/cluster/cluster.conf
> - cman_tool version -r <new version>
> 
> However, following the cman_tool code down to the kernel module part, all it does is to update the internal config_version variable to be the new version on all nodes. From the cman-kernel source (RHEL4 U4 SRPMS), file membership.c:
> 
> static int do_process_reconfig(struct msghdr *msg, char *buf, int len)
> {
> 	...
> 
>         case RECONFIG_PARAM_CONFIG_VERSION:
>                 config_version = val;
>                 break;
> 	...
> }
> 
> No configuration is reread, so it does not matter what you change in the configuration file, CMAN will never know about it until it is restarted. Similarly, I found out that qdiskd never updates the configuration, in fact it is listed as TODO ( 2) Poll ccsd for configuration changes. ).
> 
> It looks like the RHEL5 branch of the CMAN code does reread the configuration (calling read_ccs_nodes), so any change is updated. The qdisk code still shows the ccsd poll in the TODO list.
> 
> So, straight to the questions: are there any plans to change the RHEL4 code to make CMAN and qdisk get the configuration changes without needing to restart? Should I file a bugzilla against this?
> 

No, there are no plans to change this behaviour in RHEL4. if you want to change
the votes of a node you will need to use cman_tool votes -v<n>

-- 

patrick