[Bug 254840] NFSv4.1/4.2 client does not do a BindConnectionToSession for new TCP connections

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254840

            Bug ID: 254840
           Summary: NFSv4.1/4.2 client does not do a
                    BindConnectionToSession for new TCP connections
           Product: Base System
           Version: Unspecified
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: rmacklem at FreeBSD.org

Created attachment 223883
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=223883&action=edit
fix NFSv4.1/4.2 client to do a BindConnectionToSession to maintain the
backchannel

When the FreeBSD NFS client does a 4.1/4.2 mount
and the nfscbd(8) daemon is running, it binds the
TCP connection to both the fore (client->server RPCs)
and back (server->client callback RPCs) via CreateSession.

When the client finds the NFS server unresponsive,
it creates a new TCP connection. It then does an RPC
with a Sequence operation in it, binding the new
connection to the fore channel, but not the back
channel.
--> callback RPCs can no longer work.

The attachment patch modifies the client so that
the krpc does a BindConnectionToSession RPC as the
first RPC on the new connection, so that both the
fore and back channels are bound, as the were for
the original connection.

Loss of a back channel/ability to do callback RPCs
only affects delegations and pNFS.
--> Until patched the workaround is to not run
    the nfscbd(8) daemon on the client so that
    callbacks are never enabled and the NFSv4.n
    server should never issue delegations to the
    client.

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