[libvirt] Use flock() instead of fcntl()

[Jim Fehlig]

Daniel P. Berrange wrote:
> On Thu, Jul 25, 2013 at 12:07:44PM +0200, David Weber wrote:
>   
>> SUSE advises to use indirect leases which we also want to avoid:
>> https://www.suse.com/documentation//sled11/book_kvm/?page=/documentation//sled11/book_kvm/data/sec_libvirt_storage_locking.html
>>
>> "virtlockd's default configuration does not allow you to lock disk files placed 
>> on a shared file system (for example NFS or OCFS2). Locking on these file 
>> systems requires you to specify a lockspace directory on the VM Host Server by 
>> setting"
>>
>> Although that's not completely correct because NFS supports fcntl()
>>     
>
> That's just badly written explanation for that config setting. It should
> really be saying that the default configuration does not provide protection
> across multiple hosts for file paths which are not visible via a shared
> filesystem. eg a SAN LUN in /dev/sdNNN won't be protected in the default
> config.
>   

Agreed, poorly worded.  I've submitted feedback to the doc team with
suggested text improvement.

Regards,
Jim