On Wed, 2011-10-05 at 19:21 -0400, Matt W. Benjamin wrote:
> Hi,
>
> There seem to be legitimate reasons for an (NFSv4.1) client and/or server to prefer a dedicated callback channel.
That would be an assertion that is missing a lot of context and
explanation. Why should my client bother to support such a server?
> If a server wants this result, it seems from the language of 18.36.3 that it should indicate it by not setting CREATE_SESSION4_FLAG_CONN_BACK_CHAN in csr_flags in the CREATE_SESSION response, presuming the flag is set in the corresponding csa_flags argument (it's not allowed to set it otherwise). The client may respond with BIND_CONN_TO_SESSION on a new channel, setting bctsa_dir to CDFC4_BACK.
Nope. The exact wording is:
If CREATE_SESSION4_FLAG_CONN_BACK_CHAN is set in csa_flags, the
client is requesting that the connection over which the
CREATE_SESSION operation arrived be associated with the
session's backchannel in addition to its fore channel. If the
server agrees, it sets CREATE_SESSION4_FLAG_CONN_BACK_CHAN in
the result field csr_flags. If
CREATE_SESSION4_FLAG_CONN_BACK_CHAN is not set in csa_flags,
then CREATE_SESSION4_FLAG_CONN_BACK_CHAN MUST NOT be set in
csr_flags.
I see nothing there to indicate that the server is able to request a
dedicated backchannel. All it says is that the server may refuse a
backchannel on this particular connection.
> Currently, the Linux and I believe also the CITI Windows client always propose channels in both directions. The Linux mainline Linux client doesn't know how to BIND_CONN_TO_SESSION, so trivially it won't negotiate any back channel if a server didn't agree to both directions today, either. I've experimentally implemented a "fallback" model in a Linux client and (partly in a) Ganesha server. I'd appreciate any feedback on the idea.
Yep. As I said, why should we bother adding support for servers that
don't? I can function perfectly well without pNFS support or delegation
support in such a case. Performance will suck, but why do I care?
Trond
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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