Re: State of NFSv4 VolatileFilehandles

[Christoph Hellwig <hch@infradead.org>]

On Fri, Aug 05, 2011 at 03:16:10PM -0400, J. Bruce Fields wrote:
> > Another scheme is to disconnect the file handles from the inode number.
> > I implemented this a couple years ago for a customer.  Basically add
> > an extended attribute into each inode that contains the nfs file handle,
> > and that handle stays the same independent of the inode number.  The
> > added complexity is that you need a new lookup data structure mapping
> 
> And that data structure should be persistent--how were you storing it?

In this case it was in a clustered database in userspace, which I didn't
really touch directly.  If doing outside of such an appliance I would
add a btree to XFS to do the mapping. 

> > from your nfs handle to something that can be used to find the inode
> > (inode number typically).
> 
> Interesting, I've wondered before how well that would work.  Any lessons
> learned?

Don't store the data in userspace, it just makes life hard :)  The
basic idea actually was pretty straight forward, and if doing it using
the xfs btree I mentioned above fairly easy.  Other filesystems might or
might not heave similar easily reusable persistant lookup data structures.