Possibility to convert to exclusive active (opened) volume on clustered VG

[Zdenek Kabelac <zkabelac@redhat.com>]

Dne 6.12.2013 05:10, Raman napsal(a):
> Hello,
>
> Currently there is no way to convert opened volume from CR to EX or
> from EX to CR lock type on clustered volume group. The only way is to
> deactivate volume and activate it exclusively again. Example:
>
> Simple cman cluster:
> [root at clvmd2 ~]# cat /etc/cluster/cluster.conf
> <?xml version="1.0"?>
> <cluster config_version="1" name="clu">
>          <clusternodes>
>                  <clusternode name="clvmd1" nodeid="1"/>
>                  <clusternode name="clvmd2" nodeid="2"/>
>          </clusternodes>
>          <cman broadcast="yes" port="5501"/>
>          <totem token="60000"/>
> </cluster>
>
> Clustered volume group:
> [root at clvmd1 ~]# vgs --noheadings
>    vg     1   1   0 wz--nc 9.31g 9.21g
>
> Single volume activated on both nodes:
> [root at clvmd1 ~]# lvs --noheadings
>    lv1  vg   -wi-a----- 100.00m
> [root at clvmd2 ~]# lvs --noheadings
>    lv1  vg   -wi-a----- 100.00m
>
> Deactivating on second node and trying to acquire volume exclusively on
> the first node:
> [root at clvmd2 ~]# lvchange -aln vg/lv1
> [root at clvmd1 ~]# lvchange -ae vg/lv1
>    Error locking on node clvmd1: Device or resource busy
> [root at clvmd1 ~]#
>
> But works fine with deactivating cycle:
> [root at clvmd1 ~]# lvchange -aln vg/lv1 && lvs --noheading
>    lv1  vg   -wi------- 100.00m
> [root at clvmd1 ~]# lvchange -ae vg/lv1 && lvs --noheading
>    lv1  vg   -wi-a----- 100.00m
> [root at clvmd1 ~]#
>
> Proposed patch tries to solve this problem allowing lock conversion
> for activated volumes on clustered volume groups.


Patch looks mostly good - but has one 'tiny' problem which is unfortunately 
not so easy to resolve.

+#define LCK_CONVERT	0x00000800U	/* Try lock conversion */

I do not know how old code are you are patching - but recent upstream git has 
this bit already in use:

#define LCK_REMOTE	0x00000800U	/* Propagate to remote nodes only */


And the protocol is awkward to extend (all bits are already in use).

So the question is if we are able to find some bit combination
to use it uniquely for activate_lv_excl_local_convert()?


Zdenek