Re: + knfsd-exportfs-add-exportfsh-header-fix.patch added to -mm tree

[Neil Brown <neilb@suse.de>]

On Wednesday May 16, sfrench@us.ibm.com wrote:
> Any ideas what are the minimum export operation(s) that cifs would need to 
> add to export under nfsd?  It was not clear to me after reading the 
> Exporting document in Documentation directory.

You need to be able to map a dentry to a filehandle (you get about 20
bytes) and back again.
If CIFS provides some fix-length identifier for files, then you might
be able to do it.  If not, cannot really do it at all.  And I suspect
the later.  (There are other requirements, like get_parent, but we
could probably work around those if we really needed to).

Theoretically, you could make it work with NFSv4 and volatile file
handles, but I doubt it would really work in practice.  I don't think
the "volatile" concept quite stretch as far as you would need.

Probably the best way to nfs-export a CIFS filesystem is to use the
user-space nfs server.  It caches recently used filenames and uses a
filehandle which is a hash of the name.  It works on a best-effort
basis, and if, for example, the server restarts, you will lose
connections to open files.  While it is not perfect, it can be very
useful in some situations.

NeilBrown