Re: [nfsv4] [[e-mail]: New Version Notification for draft-hellwig-nfsv4-rdma-layout-00.txt]

[Christoph Hellwig <[e-mail]>]

On Mon, Jul 17, 2017 at 11:49:35AM +0200, Chuck Lever wrote:
> The connection model is critical, because the handles returned
> to clients can work only on one connection (QP). For example,
> you can't assume that NFS/RDMA will be used to access the MDS,
> nor can you assume that the MDS and DS's are accessed through
> the same HCA/RNIC on the same connection.

My crappy prototype wasn't even tested using NFS/RDMA, but the
way it opens this additional backchannel is a mess, so I wanted
to go back to the drawing board before writing anything down -
what I had is defintively not how I want it to look like in
the end.

> To make it work, there will have to be some way of binding a
> layout (containing handles) to a particular connection to a
> particular storage device.

My original idea was to open explicit new connections for it,
mostly so that the QP won't have to deal with any of the
NFS/RDMA issues and can be used purely for the operations of
the layout. 

> Also, if the connection to a DS is lost, more than a
> reconnect is necessary. The client will need to take steps to
> get the server to re-register the memory and send fresh
> handles.

Yes - a connection loss with this layout is an implicit CB_RECALL
with LAYOUTRECALL4_ALL scope.