nfs4.1: implement BACKCHANNEL_CTL operation

Motivation:
BACKCHANNEL_CTL allows clients to replace security flavor of callback
channel. Up to now, nfs4j doesn't support it.

Modification:
Add OperationBACKCHANNEL_CTL that will replace security flavor of
backchannel for nfsv4.1 clients.

Result:
better spec support.

Acked-by: Marina Sahakyan
Target: master

Author: kofemann

core/src/main/java/org/dcache/nfs/v4/MDSOperationExecutor.java

@@ -107,6 +107,8 @@ protected AbstractNFSv4Operation getOperation(nfs_argop4 op) {
                 return new OperationWRITE(op);
             case nfs_opnum4.OP_RELEASE_LOCKOWNER:
                 return new OperationRELEASE_LOCKOWNER(op);
+            case nfs_opnum4.OP_BACKCHANNEL_CTL:
+                return new OperationBACKCHANNEL_CTL(op);
             /**
              *  NFSv4.1 (pNFS)
              */

core/src/main/java/org/dcache/nfs/v4/OperationBACKCHANNEL_CTL.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2025 Deutsches Elektronen-Synchroton,
+ * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this program (see the file COPYING.LIB for more
+ * details); if not, write to the Free Software Foundation, Inc.,
+ * 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+package org.dcache.nfs.v4;
+
+import org.dcache.nfs.ChimeraNFSException;
+import org.dcache.nfs.nfsstat;
+import org.dcache.nfs.status.InvalException;
+import org.dcache.nfs.status.NfsIoException;
+import org.dcache.nfs.status.NotSuppException;
+import org.dcache.nfs.v4.xdr.nfs4_prot;
+import org.dcache.nfs.v4.xdr.nfs_argop4;
+import org.dcache.nfs.v4.xdr.nfs_opnum4;
+import org.dcache.nfs.v4.xdr.nfs_resop4;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.concurrent.TimeoutException;
+
+public class OperationBACKCHANNEL_CTL extends AbstractNFSv4Operation {
+
+    public static final Logger LOG = LoggerFactory.getLogger(OperationBACKCHANNEL_CTL.class);
+
+
+    public OperationBACKCHANNEL_CTL(nfs_argop4 op) {
+        super(op, nfs_opnum4.OP_BACKCHANNEL_CTL);
+    }
+
+    @Override
+    public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNFSException {
+
+        if( context.getMinorversion() == 0) {
+            throw new NotSuppException("Backchannel update for minor version " + context.getMinorversion() + " not supported");
+        }
+
+        var session = context.getSession();
+        var cb = new ClientCB(
+                context.getRpcCall().getTransport().getPeerTransport(),
+                _args.opbackchannel_ctl.bca_cb_program.value,
+                context.getMinorversion(),
+                session.id(),
+                session.getMaxCbOps(),
+                _args.opbackchannel_ctl.bca_sec_parms);
+
+        try {
+            cb.cbPing();
+            session.getClient().setCB(cb);
+        } catch (IOException | TimeoutException e) {
+            LOG.warn("Failed to to replace backchannel for {} : {}", session.getClient(), e.getMessage());
+            throw new NfsIoException(e.getMessage());
+        }
+
+        result.opbackchannel_ctl.bcr_status = nfsstat.NFS_OK;
+    }
+}