[Cluster-devel] Re: [PATCH 1/2] NLM failover unlock commands

[J. Bruce Fields]

On Thu, Jan 17, 2008 at 10:48:56AM -0500, Wendy Cheng wrote:
> J. Bruce Fields wrote:
>> Remind me: why do we need both per-ip and per-filesystem methods?  In
>> practice, I assume that we'll always do *both*?
>>   
>
> Failover normally is done via virtual IP address - so per-ip base method  
> should be the core routine. However, for non-cluster filesystem such as  
> ext3/4, changing server also implies umount. If there are clients not  
> following rule and obtaining locks via different ip interfaces, umount  
> would fail that ends up aborting the failover process. That's the place  
> we need the per-filesystem method.
>
> ServerA:
> 1. Tear down the IP address
> 2. Unexport the path
> 3. Write IP to /proc/fs/nfsd/unlock_ip to unlock files
> 4. If unmount required,
> write path name to /proc/fs/nfsd/unlock_filesystem, then unmount.
> 5. Signal peer to begin take-over.
>
> Sometime ago we were looking at "export name" as the core method (so  
> per-filesystem method is a subset of that). Unfortunately, the prototype  
> efforts showed the code would be too intrusive (if filesystem sub-tree  
> is exported).
>> We're migrating clients by moving a server ip address from one node to
>> another.  And I assume we're permitting at most one node to export each
>> filesystem at a time.  So it *should* be the case that the set of locks
>> held on the filesystem(s) that are moving are the same as the set of
>> locks held by the virtual ip that is moving.
>>   
>
> This is true for non-cluster filesystem. But a cluster filesystem can be  
> exported from multiple servers.

But that last sentence:

	it *should* be the case that the set of locks held on the
	filesystem(s) that are moving are the same as the set of locks
	held by the virtual ip that is moving.

is still true in the cluster filesystem case, right?

--b.