NFS: Use NFSv4.2's OFFLOAD_STATUS operation

We've found that there are cases where a transport disconnection
results in the loss of callback RPCs. NFS servers typically do not
retransmit callback operations after a disconnect.

This can be a problem for the Linux NFS client's current
implementation of asynchronous COPY, which waits indefinitely for a
CB_OFFLOAD callback. If a transport disconnect occurs while an async
COPY is running, there's a good chance the client will never get the
completing CB_OFFLOAD.

Fix this by implementing the OFFLOAD_STATUS operation so that the
Linux NFS client can probe the NFS server if it doesn't see a
CB_OFFLOAD in a reasonable amount of time.

This patch implements a simplistic check. As future work, the client
might also be able to detect whether there is no forward progress on
the request asynchronous COPY operation, and CANCEL it.

Suggested-by: Olga Kornievskaia <kolga@netapp.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218735


Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Link: https://lore.kernel.org/r/20250113153235.48706-15-cel@kernel.org


Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>