[Linux-cluster] DLM user API for lock value block

[David Teigland]

On Tue, Dec 06, 2016 at 05:18:44PM +0100, Jean-Marc Saffroy wrote:
> Hi,
> 
> I am trying to use the DLM userland API (libdlm3), and while I was able to 
> do plain lock acquisitions and conversions, I am stuck trying to update 
> and then read the lock value block.
> 
> Does anyone have working examples of this? I did look at the rhdlmbook 
> doc, but couldn't fine one.

I haven't looked at your test to check if you're actually seeing this bug,
but you'll want this fix in any case:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/fs/dlm/user.c?id=b96f465035f9fae83c1d8de3e80eecfe6877608c

In the following lvmlockd code, you can see an example of working around
that bug if you don't have immediate access to a newer kernel:

https://git.fedorahosted.org/cgit/lvm2.git/tree/daemons/lvmlockd/lvmlockd-dlm.c

There are some other random userland tests here that use lvbs:

https://fedorapeople.org/cgit/teigland/public_git/dct-stuff.git/tree/dlm

Dave