Re: [PATCH/RFC 0/7] Volatile Filehandle Client-side Support

["J. Bruce Fields" <bfields@fieldses.org>]

On Fri, Jan 13, 2012 at 11:09:14AM -0600, Malahal Naineni wrote:
> Trond Myklebust [Trond.Myklebust@netapp.com] wrote:
> > On Mon, 2011-11-14 at 08:07 +1100, NeilBrown wrote:
> > 
> > > If a server has objects that are never renamed, it can easily use volatile
> > > file handles.
> > > If a server has objects which can be renamed and wants to use volatile file
> > > handles, then if such an object is open and is about to be renamed, it must
> > > first log to stable storage some mapping to allow it to access the file from
> > > the old volatile file handle.  And of course it cannot allow renames during
> > > the grace period, but I think we already have that.
> > > Also, if the VFH is such that it will be  lost on a reboot, the server must
> > > log it to stable storage before allowing an open.
> > 
> > BTW: If the namespace is stable, then the server can easily implement
> > permanent filehandles. Use a hash of the pathname as the filehandle, and
> > set up a hidden directory ('/.filehandles') containing symlinks that map
> > said hash back to the correct pathname. No need for volatile
> > filehandles.
> 
> Neil and Trond, one of our use cases is for a read only file system. The
> name space is stable and Volatile File Handle support should not have
> any issues under those conditions, correct?

Dumb question: remind me which filesystem your exporting that can't
already generate stable filehandles?

--b.

> 
> Trond, trying to understand how we can make file handles permanent at
> the servers with your ideas. We do use linux NFS server. Looks like the
> server needs a new config parameter to hide '/.filehandles' and use it
> for storing permanent file handles. Also, the solution needs a tool
> that generates/populates './filehandles' directory. I don't know how
> best we should handle hash collisions at this point (shouldn't be an
> issue once we agree to a method though). Anything else I am missing?
> 
> Any thoughts from linux NFS server community? Is this approach
> acceptable?
> 
> Regards, Malahal.
>