[linux-lvm] A couple of questions on locking library

[Zdenek Kabelac]

Dne 31. 05. 19 v 9:13 Shawn Guo napsal(a):
> Hi David, Zdenek,
> 
> Comparing to stable-2.02 branch, I noticed that there are significant
> changes around locking infrastructure on master branch.  I have a
> couple of questions regarding to these changes.
> 
> 1. I see External Locking support was removed as part of clvmd
> removal. What's the reason for dropping External Locking support?  I'm
> asking because we are investigating the possibility to use hardware
> assisted locking for cluster, in form of External Locking extension.
> 
> 2. It seems there have never been real support for LV (Logic Volume)
> locking.  On stable-2.02 branch, the LV locking interface is used as
> activation path instead of real locking on LV.  And on master branch,
> activation path gets separated off from locking infrastructure.  As
> the result, the LV interface is dropped completely from locking
> infrastructure.  My question is why there have never been LV locking
> support.  Is the LV locking support an invalid requirement at all?  Or
> it's just because no one cares about it enough to add the support?
> 
> Thanks for your time, and appreciate any comment you would give here.

With stable-2.02 branch - there was always per-LV locking.
The 'state' of the LV was matching state of lock.

http://people.redhat.com/agk/talks/CLVM-UKUUG2007/

See the 'DLM – Distributed Lock Manager'

The lock however was always took only for top-level LV - never for those 
component LVs.

--

There is however believe, that users no longer use volumes with shared 
activation (active at one time on multiple hosts) - so lvm2 is now being moved
transformed to theoretically less complex locking scheme...

Regards

Zdenek