diff --git a/core/src/main/java/org/dcache/nfs/util/Opaque.java b/core/src/main/java/org/dcache/nfs/util/Opaque.java
index bec1ddba..41dc21f9 100644
--- a/core/src/main/java/org/dcache/nfs/util/Opaque.java
+++ b/core/src/main/java/org/dcache/nfs/util/Opaque.java
@@ -20,10 +20,13 @@
 package org.dcache.nfs.util;
 
 import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 import java.util.Arrays;
 import java.util.Base64;
 import java.util.Objects;
 
+import org.dcache.oncrpc4j.util.Bytes;
+
 /**
  * Describes something that can be used as a key for {@link java.util.HashMap} and that can be converted to a
  * {@code byte[]} and a Base64 string representation.
@@ -85,6 +88,9 @@ static Opaque forBytes(ByteBuffer buf, int length) {
      * @see #toImmutableOpaque()
      */
     static Opaque forMutableByteBuffer(ByteBuffer buf, int index, int length) {
+        if (buf.order() != ByteOrder.BIG_ENDIAN) {
+            buf = buf.duplicate();
+        }
         return new OpaqueBufferImpl(buf, index, length);
     }
 
@@ -174,7 +180,23 @@ default void putBytes(ByteBuffer buf) {
     @Override
     boolean equals(Object o);
 
-    class OpaqueImpl implements Opaque {
+    /**
+     * Returns the byte stored at the given position.
+     * 
+     * @param byteOffset The byte offset
+     * @return The byte.
+     */
+    byte byteAt(int byteOffset);
+
+    /**
+     * Returns the {@code long} stored at the given position, using big-endian byte order.
+     * 
+     * @param byteOffset The byte offset
+     * @return The long.
+     */
+    long longAt(int byteOffset);
+
+    public class OpaqueImpl implements Opaque {
         final byte[] _opaque;
 
         OpaqueImpl(byte[] opaque) {
@@ -253,6 +275,16 @@ public int numBytes() {
         public Opaque toImmutableOpaque() {
             return Opaque.forBytes(_opaque);
         }
+
+        @Override
+        public byte byteAt(int position) {
+            return _opaque[position];
+        }
+
+        @Override
+        public long longAt(int byteOffset) {
+            return Bytes.getLong(_opaque, byteOffset);
+        }
     }
 
     final class OpaqueImmutableImpl extends OpaqueImpl {
@@ -368,5 +400,15 @@ public boolean equals(Object o) {
         public String toString() {
             return super.toString() + "[" + toBase64() + "]";
         }
+
+        @Override
+        public byte byteAt(int position) {
+            return buf.get(position);
+        }
+
+        @Override
+        public long longAt(int byteOffset) {
+            return buf.getLong(byteOffset);
+        }
     }
 }
diff --git a/core/src/main/java/org/dcache/nfs/v4/FileTracker.java b/core/src/main/java/org/dcache/nfs/v4/FileTracker.java
index 1ff0b9a4..81d31558 100644
--- a/core/src/main/java/org/dcache/nfs/v4/FileTracker.java
+++ b/core/src/main/java/org/dcache/nfs/v4/FileTracker.java
@@ -315,9 +315,9 @@ public OpenRecord addOpen(NFS4Client client, StateOwner owner, Inode inode, int
                         os.shareDenySeen |= 1 << ((shareDeny & nfs4_prot.OPEN4_SHARE_ACCESS_BOTH) - 1);
                     }
 
-                    os.stateid.seqid++;
+                    os.stateid.bumpSeqid();
                     // we need to return copy to avoid modification by concurrent opens
-                    var openStateid = new stateid4(os.stateid.other, os.stateid.seqid);
+                    var openStateid = os.stateid.clone();
 
                     // yet another open from the same client. Let's check if we can delegate.
                     if (canDelegateRead && (os.shareAccess
@@ -342,10 +342,10 @@ public OpenRecord addOpen(NFS4Client client, StateOwner owner, Inode inode, int
             OpenState openState = new OpenState(client, owner, stateid, shareAccess, shareDeny);
             opens.add(openState);
             state.addDisposeListener(s -> removeOpen(inode, stateid));
-            stateid.seqid++;
+            stateid.bumpSeqid();
 
             // we need to return copy to avoid modification by concurrent opens
-            var openStateid = new stateid4(stateid.other, stateid.seqid);
+            var openStateid = stateid.clone();
 
             // REVISIT: currently only read-delegations are supported
             if (canDelegateRead && (wantReadDelegation || adlHeuristic.shouldDelegate(client, inode))) {
@@ -408,9 +408,9 @@ public stateid4 downgradeOpen(NFS4Client client, stateid4 stateid, Inode inode,
             os.shareAccess = shareAccess;
             os.shareDeny = shareDeny;
 
-            os.stateid.seqid++;
+            os.stateid.bumpSeqid();
             // we need to return copy to avoid modification by concurrent opens
-            return new stateid4(os.stateid.other, os.stateid.seqid);
+            return os.stateid.clone();
         } finally {
             lock.unlock();
         }
@@ -463,16 +463,21 @@ public void delegationReturn(NFS4Client client, stateid4 stateid, Inode inode)
      */
     public int getShareAccess(NFS4Client client, Inode inode, stateid4 stateid)
             throws ChimeraNFSException {
+        Opaque stateIdOpaque = stateid.getOpaque();
+        return getShareAccess(client, inode, stateIdOpaque);
+    }
 
+    public int getShareAccess(NFS4Client client, Inode inode, Opaque stateid)
+            throws ChimeraNFSException {
         Opaque fileId = inode.getFileIdKey();
         Lock lock = filesLock.get(fileId);
         lock.lock();
         try {
 
-            switch (stateid.other[11]) {
+            switch (stateid4.getType(stateid)) {
                 case Stateids.LOCK_STATE_ID:
                     NFS4State lockState = client.state(stateid);
-                    stateid = lockState.getOpenState().stateid();
+                    stateid = lockState.getOpenState().stateid().getOpaque();
                     // fall through
                 case Stateids.OPEN_STATE_ID: {
                     final List<OpenState> opens = files.get(fileId);
@@ -481,10 +486,10 @@ public int getShareAccess(NFS4Client client, Inode inode, stateid4 stateid)
                         throw new BadStateidException("no matching open");
                     }
 
-                    final stateid4 openStateid = stateid;
+                    final Opaque openStateid = stateid;
                     return opens.stream()
                             .filter(s -> client.getId() == s.client.getId())
-                            .filter(s -> s.stateid.equals(openStateid))
+                            .filter(s -> s.stateid.getOpaque().equals(openStateid))
                             .mapToInt(OpenState::getShareAccess)
                             .findAny()
                             .orElseThrow(BadStateidException::new);
@@ -496,11 +501,11 @@ public int getShareAccess(NFS4Client client, Inode inode, stateid4 stateid)
                         throw new BadStateidException("no delegation found");
                     }
 
-                    stateid4 delegationStateid = stateid;
+                    Opaque delegationStateid = stateid;
 
                     var delegation = fileDelegations.stream()
                             .filter(d -> d.client().getId().equals(client.getId()))
-                            .filter(d -> d.delegationStateid().stateid().equals(delegationStateid))
+                            .filter(d -> d.delegationStateid().stateid().getOpaque().equals(delegationStateid))
                             .findAny()
                             .orElseThrow(BadStateidException::new);
 
diff --git a/core/src/main/java/org/dcache/nfs/v4/NFS4Client.java b/core/src/main/java/org/dcache/nfs/v4/NFS4Client.java
index 4afbd04b..8eff70f3 100644
--- a/core/src/main/java/org/dcache/nfs/v4/NFS4Client.java
+++ b/core/src/main/java/org/dcache/nfs/v4/NFS4Client.java
@@ -117,7 +117,7 @@ public class NFS4Client {
      */
     private int _sessionSequence = 1;
 
-    private final Map<stateid4, NFS4State> _clientStates = new ConcurrentHashMap<>();
+    private final Map<Opaque, NFS4State> _clientStates = new ConcurrentHashMap<>();
 
     /**
      * sessions associated with the client
@@ -334,18 +334,20 @@ private NFS4State createState(StateOwner stateOwner, byte type, NFS4State openSt
 
         NFS4State state = new NFS4State(openState, stateOwner, _stateHandler.createStateId(this, type, _stateIdCounter
                 .incrementAndGet()));
+        stateid4 stateId = state.stateid();
+        Opaque opaque = stateId.getOpaque();
         if (openState != null) {
             openState.addDisposeListener(s -> {
                 // remove and dispose derived states.
-                NFS4State nfsState = _clientStates.get(state.stateid());
+                NFS4State nfsState = _clientStates.get(opaque);
                 if (nfsState != null) {
                     _log.debug("removing derived state {}", nfsState);
                     nfsState.tryDispose();
                 }
-                _clientStates.remove(state.stateid());
+                _clientStates.remove(opaque);
             });
         }
-        _clientStates.put(state.stateid(), state);
+        _clientStates.put(opaque, state);
         return state;
     }
 
@@ -410,29 +412,34 @@ public NFS4State createServerSideCopyState(StateOwner stateOwner, NFS4State open
     }
 
     public void releaseState(stateid4 stateid) throws ChimeraNFSException {
+        Opaque opaque = stateid.getOpaque();
 
-        NFS4State state = _clientStates.get(stateid);
+        NFS4State state = _clientStates.get(opaque);
         if (state == null) {
             throw new BadStateidException("State not known to the client: " + stateid);
         }
         state.disposeIgnoreFailures();
-        _clientStates.remove(stateid);
+        _clientStates.remove(opaque);
     }
 
     public void tryReleaseState(stateid4 stateid) throws ChimeraNFSException {
 
-        NFS4State state = _clientStates.get(stateid);
+        NFS4State state = _clientStates.get(stateid.getOpaque());
         if (state == null) {
             throw new BadStateidException("State not known to the client: " + stateid);
         }
         state.tryDispose();
-        _clientStates.remove(stateid);
+        _clientStates.remove(stateid.getOpaque());
     }
 
     public NFS4State state(stateid4 stateid) throws ChimeraNFSException {
-        NFS4State state = _clientStates.get(stateid);
+        return state(stateid.getOpaque());
+    }
+
+    public NFS4State state(Opaque stateidOpaque) throws ChimeraNFSException {
+        NFS4State state = _clientStates.get(stateidOpaque);
         if (state == null) {
-            throw new BadStateidException("State not known to the client: " + stateid);
+            throw new BadStateidException("State not known to the client: " + stateidOpaque);
         }
         return state;
     }
@@ -534,7 +541,7 @@ public boolean hasState() {
      * @param state to attach
      */
     public void attachState(NFS4State state) {
-        _clientStates.put(state.stateid(), state);
+        _clientStates.put(state.stateid().getOpaque(), state);
     }
 
     /**
@@ -543,7 +550,7 @@ public void attachState(NFS4State state) {
      * @param state to detach
      */
     public void detachState(NFS4State state) {
-        _clientStates.remove(state.stateid());
+        _clientStates.remove(state.stateid().getOpaque());
     }
 
     @GuardedBy("this")
diff --git a/core/src/main/java/org/dcache/nfs/v4/NFS4State.java b/core/src/main/java/org/dcache/nfs/v4/NFS4State.java
index fa506e13..4a7b0c4d 100644
--- a/core/src/main/java/org/dcache/nfs/v4/NFS4State.java
+++ b/core/src/main/java/org/dcache/nfs/v4/NFS4State.java
@@ -68,7 +68,7 @@ public NFS4State(NFS4State openState, StateOwner owner, stateid4 stateid) {
     }
 
     public void bumpSeqid() {
-        ++_stateid.seqid;
+        _stateid.bumpSeqid();
     }
 
     public stateid4 stateid() {
diff --git a/core/src/main/java/org/dcache/nfs/v4/NFSServerV41.java b/core/src/main/java/org/dcache/nfs/v4/NFSServerV41.java
index e1da08e6..85b6588d 100644
--- a/core/src/main/java/org/dcache/nfs/v4/NFSServerV41.java
+++ b/core/src/main/java/org/dcache/nfs/v4/NFSServerV41.java
@@ -134,7 +134,7 @@ public COMPOUND4res NFSPROC4_COMPOUND_4(RpcCall call$, COMPOUND4args arg1) {
             }
             res.resarray = new ArrayList<>(arg1.argarray.length);
 
-            VirtualFileSystem fs = new PseudoFs(_fs, call$, _exportTable);
+            VirtualFileSystem fs = new PseudoFs(_fs, call$, _exportTable, _statHandler);
 
             CompoundContextBuilder builder = new CompoundContextBuilder()
                     .withMinorversion(arg1.minorversion.value)
diff --git a/core/src/main/java/org/dcache/nfs/v4/NFSv4StateHandler.java b/core/src/main/java/org/dcache/nfs/v4/NFSv4StateHandler.java
index b7d64a4d..afc62a6a 100644
--- a/core/src/main/java/org/dcache/nfs/v4/NFSv4StateHandler.java
+++ b/core/src/main/java/org/dcache/nfs/v4/NFSv4StateHandler.java
@@ -237,13 +237,22 @@ public NFS4Client getClient(clientid4 clientid) throws StaleClientidException {
         }
     }
 
+    public NFS4Client getClientIfExists(long clientId) {
+        _readLock.lock();
+        try {
+            return _clientsByServerId.get(new clientid4(clientId));
+        } finally {
+            _readLock.unlock();
+        }
+    }
+
     public NFS4Client getClientIdByStateId(stateid4 stateId) throws ChimeraNFSException {
 
         _readLock.lock();
         try {
             checkState(_running, "NFS state handler not running");
 
-            clientid4 clientId = new clientid4(Bytes.getLong(stateId.other, 0));
+            clientid4 clientId = new clientid4(stateId.getClientId());
             NFS4Client client = _clientsByServerId.get(clientId);
             if (client == null) {
                 throw new BadStateidException("no client for stateid: " + stateId);
@@ -439,7 +448,7 @@ public int getInstanceId() {
      * @return state hander id.
      */
     public static int getInstanceId(stateid4 stateid) {
-        long clientid = Bytes.getLong(stateid.other, 0);
+        long clientid = stateid.getClientId();
         return (int) (clientid >> 16) & 0xFFFF;
     }
 
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationCLOSE.java b/core/src/main/java/org/dcache/nfs/v4/OperationCLOSE.java
index ff4e1850..82504ed8 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationCLOSE.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationCLOSE.java
@@ -29,6 +29,7 @@
 import org.dcache.nfs.v4.xdr.nfs_resop4;
 import org.dcache.nfs.v4.xdr.stateid4;
 import org.dcache.nfs.vfs.Inode;
+import org.dcache.nfs.vfs.VirtualFileSystem;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -59,6 +60,11 @@ public void process(CompoundContext context, nfs_resop4 result)
         NFS4State nfsState = client.state(stateid);
         Stateids.checkStateId(nfsState.stateid(), stateid);
 
+        VirtualFileSystem fs = context.getFs();
+        if (fs != null) {
+            fs.close(stateid.getOpaque());
+        }
+
         if (context.getMinorversion() == 0) {
             nfsState.getStateOwner().acceptAsNextSequence(_args.opclose.seqid);
             client.updateLeaseTime();
@@ -68,6 +74,5 @@ public void process(CompoundContext context, nfs_resop4 result)
 
         res.open_stateid = Stateids.invalidStateId();
         res.status = nfsstat.NFS_OK;
-
     }
 }
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationCOMMIT.java b/core/src/main/java/org/dcache/nfs/v4/OperationCOMMIT.java
index d534ab26..96b45d12 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationCOMMIT.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationCOMMIT.java
@@ -28,6 +28,7 @@
 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.dcache.nfs.v4.xdr.stateid4;
 import org.dcache.nfs.vfs.Inode;
 
 public class OperationCOMMIT extends AbstractNFSv4Operation {
@@ -42,8 +43,11 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
         final COMMIT4res res = result.opcommit;
         Inode inode = context.currentInode();
 
+        stateid4 stateid = Stateids.getCurrentStateidIfNeeded(context, _args.opwrite.stateid);
+
         _args.opcommit.offset.checkOverflow(_args.opcommit.count.value, "offset + length overflow");
-        context.getFs().commit(inode, _args.opcommit.offset.value, _args.opcommit.count.value);
+        context.getFs().commit(stateid.getOpaque(), inode, _args.opcommit.offset.value,
+                _args.opcommit.count.value);
 
         res.resok4 = new COMMIT4resok();
         res.resok4.writeverf = context.getRebootVerifier();
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationLOCK.java b/core/src/main/java/org/dcache/nfs/v4/OperationLOCK.java
index d3b9575b..dbff6f59 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationLOCK.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationLOCK.java
@@ -24,8 +24,10 @@
 import org.dcache.nfs.status.InvalException;
 import org.dcache.nfs.status.OpenModeException;
 import org.dcache.nfs.status.ServerFaultException;
+import org.dcache.nfs.util.Opaque;
 import org.dcache.nfs.v4.nlm.LockDeniedException;
 import org.dcache.nfs.v4.nlm.LockException;
+import org.dcache.nfs.v4.nlm.LockManager;
 import org.dcache.nfs.v4.nlm.NlmLock;
 import org.dcache.nfs.v4.xdr.LOCK4denied;
 import org.dcache.nfs.v4.xdr.LOCK4resok;
@@ -118,12 +120,12 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
 
             NlmLock lock = new NlmLock(lockOwner, _args.oplock.locktype, _args.oplock.offset.value,
                     _args.oplock.length.value);
-            context.getLm().lock(inode.getLockKey(), lock);
+            Opaque lockKey = inode.getLockKey();
+            LockManager lm = context.getLm();
+            lm.lock(lockKey, lock);
 
             // ensure, that on close locks will be released
-            lock_state.addDisposeListener(s -> {
-                context.getLm().unlockIfExists(inode.getLockKey(), lock);
-            });
+            lock_state.addDisposeListener(s -> lm.unlockIfExists(lockKey, lock));
 
             // FIXME: we might run into race condition, thus updating sedid must be fenced!
             lock_state.bumpSeqid();
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationOPEN.java b/core/src/main/java/org/dcache/nfs/v4/OperationOPEN.java
index 790f3b71..d250df4c 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationOPEN.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationOPEN.java
@@ -33,6 +33,7 @@
 import org.dcache.nfs.status.NotDirException;
 import org.dcache.nfs.status.SymlinkException;
 import org.dcache.nfs.status.WrongTypeException;
+import org.dcache.nfs.v4.FileTracker.OpenRecord;
 import org.dcache.nfs.v4.xdr.OPEN4res;
 import org.dcache.nfs.v4.xdr.OPEN4resok;
 import org.dcache.nfs.v4.xdr.aceflag4;
@@ -61,6 +62,8 @@
 import org.dcache.nfs.v4.xdr.why_no_delegation4;
 import org.dcache.nfs.vfs.Inode;
 import org.dcache.nfs.vfs.Stat;
+import org.dcache.nfs.vfs.VirtualFileSystem;
+import org.dcache.nfs.vfs.VirtualFileSystem.OpenMode;
 import org.dcache.oncrpc4j.rpc.OncRpcException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -101,6 +104,9 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
         res.resok4.cinfo = new change_info4();
         res.resok4.cinfo.atomic = true;
 
+        Inode inode;
+        VirtualFileSystem.OpenMode openMode;
+
         switch (_args.opopen.claim.claim) {
 
             case open_claim_type4.CLAIM_NULL:
@@ -118,7 +124,6 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
                 String name = NameFilter.convertName(_args.opopen.claim.file.value);
                 _log.debug("regular open for : {}", name);
 
-                Inode inode;
                 if (_args.opopen.openhow.opentype == opentype4.OPEN4_CREATE) {
 
                     boolean exclusive = (_args.opopen.openhow.how.mode == createmode4.EXCLUSIVE4)
@@ -205,13 +210,13 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
                         }
 
                     }
-
+                    openMode = OpenMode.READ_WRITE;
                 } else {
                     // no changes from us, old stat info is still good enough
                     res.resok4.cinfo.after = new changeid4(stat.getGeneration());
 
                     inode = context.getFs().lookup(context.currentInode(), name);
-                    checkCanAccess(context, inode, _args.opopen.share_access);
+                    openMode = checkCanAccess(context, inode, _args.opopen.share_access);
                 }
 
                 context.currentInode(inode);
@@ -238,7 +243,7 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
                 res.resok4.cinfo.after = new changeid4(0);
 
                 inode = context.currentInode();
-                checkCanAccess(context, inode, _args.opopen.share_access);
+                openMode = checkCanAccess(context, inode, _args.opopen.share_access);
                 break;
             case open_claim_type4.CLAIM_DELEGATE_CUR:
             case open_claim_type4.CLAIM_DELEGATE_PREV:
@@ -268,15 +273,19 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
          *
          * THis is a perfectly a valid situation as at the end file is created and only one writer is allowed.
          */
-        var openRecord = context
+        OpenRecord openRecord = context
                 .getStateHandler()
                 .getFileTracker()
                 .addOpen(client, owner, context.currentInode(),
                         _args.opopen.share_access.value,
                         _args.opopen.share_deny.value);
 
-        context.currentStateid(openRecord.openStateId());
-        res.resok4.stateid = openRecord.openStateId();
+        stateid4 openStateId = openRecord.openStateId();
+        context.currentStateid(openStateId);
+
+        context.getFs().open(openStateId.getOpaque(), inode, openMode);
+
+        res.resok4.stateid = openStateId;
         if (openRecord.hasDelegation()) {
             res.resok4.delegation.delegation_type = open_delegation_type4.OPEN_DELEGATE_READ;
             res.resok4.delegation.read = new open_read_delegation4();
@@ -294,19 +303,24 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
 
     }
 
-    private void checkCanAccess(CompoundContext context, Inode inode, uint32_t share_access) throws IOException {
+    private VirtualFileSystem.OpenMode checkCanAccess(CompoundContext context, Inode inode, uint32_t share_access)
+            throws IOException {
 
         int accessMode;
+        VirtualFileSystem.OpenMode openMode;
 
         switch (share_access.value & ~nfs4_prot.OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) {
             case nfs4_prot.OPEN4_SHARE_ACCESS_READ:
                 accessMode = nfs4_prot.ACCESS4_READ;
+                openMode = VirtualFileSystem.OpenMode.READ_ONLY;
                 break;
             case nfs4_prot.OPEN4_SHARE_ACCESS_WRITE:
                 accessMode = nfs4_prot.ACCESS4_MODIFY;
+                openMode = VirtualFileSystem.OpenMode.WRITE_ONLY;
                 break;
             case nfs4_prot.OPEN4_SHARE_ACCESS_BOTH:
                 accessMode = nfs4_prot.ACCESS4_READ | nfs4_prot.ACCESS4_MODIFY;
+                openMode = VirtualFileSystem.OpenMode.READ_WRITE;
                 break;
             default:
                 throw new InvalException("Invalid share_access mode: " + share_access.value);
@@ -328,5 +342,7 @@ private void checkCanAccess(CompoundContext context, Inode inode, uint32_t share
             default:
                 throw context.getMinorversion() == 0 ? new SymlinkException() : new WrongTypeException();
         }
+
+        return openMode;
     }
 }
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationREAD.java b/core/src/main/java/org/dcache/nfs/v4/OperationREAD.java
index 649fe457..748b8c9a 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationREAD.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationREAD.java
@@ -73,7 +73,7 @@ public void process(CompoundContext context, nfs_resop4 result) throws IOExcepti
         ByteBuffer buf = ByteBuffer.allocate(count);
 
         res.resok4 = new READ4resok();
-        int bytesRead = context.getFs().read(inode, buf, offset, res.resok4::setEOF);
+        int bytesRead = context.getFs().read(stateid.getOpaque(), inode, buf, offset, res.resok4::setEOF);
 
         if (bytesRead < 0) {
             buf.clear();
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationTEST_STATEID.java b/core/src/main/java/org/dcache/nfs/v4/OperationTEST_STATEID.java
index 09feca96..44f74da2 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationTEST_STATEID.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationTEST_STATEID.java
@@ -53,7 +53,7 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
             stateid4 statid = _args.optest_stateid.ts_stateids[i];
             try {
                 NFS4State state = client.state(statid);
-                if (state.stateid().seqid < statid.seqid) {
+                if (state.stateid().getSeqId() < statid.getSeqId()) {
                     res.tsr_resok4.tsr_status_codes[i] = nfsstat.NFSERR_OLD_STATEID;
                 } else {
                     res.tsr_resok4.tsr_status_codes[i] = nfsstat.NFS_OK;
diff --git a/core/src/main/java/org/dcache/nfs/v4/OperationWRITE.java b/core/src/main/java/org/dcache/nfs/v4/OperationWRITE.java
index 27690b02..d1b8237e 100644
--- a/core/src/main/java/org/dcache/nfs/v4/OperationWRITE.java
+++ b/core/src/main/java/org/dcache/nfs/v4/OperationWRITE.java
@@ -87,7 +87,8 @@ public void process(CompoundContext context, nfs_resop4 result) throws ChimeraNF
         }
 
         long offset = _args.opwrite.offset.value;
-        VirtualFileSystem.WriteResult writeResult = context.getFs().write(context.currentInode(),
+        VirtualFileSystem.WriteResult writeResult = context.getFs().write(
+                stateid.getOpaque(), context.currentInode(),
                 _args.opwrite.data, offset, VirtualFileSystem.StabilityLevel.fromStableHow(_args.opwrite.stable));
 
         if (writeResult.getBytesWritten() < 0) {
diff --git a/core/src/main/java/org/dcache/nfs/v4/Stateids.java b/core/src/main/java/org/dcache/nfs/v4/Stateids.java
index 01349320..51e8fa07 100644
--- a/core/src/main/java/org/dcache/nfs/v4/Stateids.java
+++ b/core/src/main/java/org/dcache/nfs/v4/Stateids.java
@@ -67,7 +67,7 @@ private Stateids() {
             (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff}, nfs4_prot.NFS4_UINT32_MAX);
 
     public static stateid4 uptodateOf(stateid4 stateid) {
-        return new stateid4(stateid.other, 0);
+        return new stateid4(stateid.getOpaque().toBytes(), 0);
     }
 
     public static stateid4 currentStateId() {
@@ -91,16 +91,17 @@ public static boolean isStateLess(stateid4 stateid) {
     }
 
     public static void checkStateId(stateid4 expected, stateid4 stateid) throws ChimeraNFSException {
-        if (stateid.seqid == 0) {
+        int seq = stateid.getSeqId();
+        if (seq == 0) {
             // so called 'most up-to-date seqid', see https://tools.ietf.org/html/rfc5661#section-8.2.2
             return;
         }
 
-        if (expected.seqid > stateid.seqid) {
-            throw new OldStateidException();
-        }
+        int expectedSeq = expected.getSeqId();
 
-        if (expected.seqid < stateid.seqid) {
+        if (expectedSeq > seq) {
+            throw new OldStateidException();
+        } else if (expectedSeq != seq) {
             throw new BadStateidException();
         }
     }
@@ -114,37 +115,37 @@ public static stateid4 getCurrentStateidIfNeeded(CompoundContext context, statei
     }
 
     public static void checkOpenStateid(stateid4 stateid) throws BadStateidException {
-        if (stateid.other[11] != OPEN_STATE_ID) {
+        if (stateid.getType() != OPEN_STATE_ID) {
             throw new BadStateidException("Not an open stateid");
         }
     }
 
     public static void checkLockStateid(stateid4 stateid) throws BadStateidException {
-        if (stateid.other[11] != LOCK_STATE_ID) {
+        if (stateid.getType() != LOCK_STATE_ID) {
             throw new BadStateidException("Not a lock stateid");
         }
     }
 
     public static void checkDelegationStateid(stateid4 stateid) throws BadStateidException {
-        if (stateid.other[11] != DELEGATION_STATE_ID) {
+        if (stateid.getType() != DELEGATION_STATE_ID) {
             throw new BadStateidException("Not a delegation stateid");
         }
     }
 
     public static void checkDirDelegationStateid(stateid4 stateid) throws BadStateidException {
-        if (stateid.other[11] != DIR_DELEGATION_STATE_ID) {
+        if (stateid.getType() != DIR_DELEGATION_STATE_ID) {
             throw new BadStateidException("Not a directory delegation stateid");
         }
     }
 
     public static void checkServerSiderCopyStateid(stateid4 stateid) throws BadStateidException {
-        if (stateid.other[11] != SSC_STATE_ID) {
+        if (stateid.getType() != SSC_STATE_ID) {
             throw new BadStateidException("Not a server-side copy stateid");
         }
     }
 
     public static void checkLayoutStateid(stateid4 stateid) throws BadStateidException {
-        if (stateid.other[11] != LAYOUT_STATE_ID) {
+        if (stateid.getType() != LAYOUT_STATE_ID) {
             throw new BadStateidException("Not a layout stateid");
         }
     }
diff --git a/core/src/main/java/org/dcache/nfs/v4/xdr/stateid4.java b/core/src/main/java/org/dcache/nfs/v4/xdr/stateid4.java
index 701775fe..90422848 100644
--- a/core/src/main/java/org/dcache/nfs/v4/xdr/stateid4.java
+++ b/core/src/main/java/org/dcache/nfs/v4/xdr/stateid4.java
@@ -20,46 +20,78 @@
 package org.dcache.nfs.v4.xdr;
 
 import java.io.IOException;
+import java.io.ObjectInputStream.GetField;
+import java.io.ObjectOutputStream.PutField;
 import java.io.Serializable;
-import java.util.Arrays;
 
+import org.dcache.nfs.util.Opaque;
 import org.dcache.oncrpc4j.rpc.OncRpcException;
 import org.dcache.oncrpc4j.xdr.XdrAble;
 import org.dcache.oncrpc4j.xdr.XdrDecodingStream;
 import org.dcache.oncrpc4j.xdr.XdrEncodingStream;
 
-import com.google.common.io.BaseEncoding;
-
-public class stateid4 implements XdrAble, Serializable {
+public class stateid4 implements XdrAble, Serializable, Cloneable {
 
     static final long serialVersionUID = -6677150504723505919L;
 
-    public int seqid;
-    public byte[] other;
+    private int seqid;
+    @SuppressWarnings("unused")
+    private byte[] other; // only declared for Java Serialization
+    private transient Opaque opaque;
 
-    public stateid4() {
+    public stateid4(XdrDecodingStream xdr) throws OncRpcException, IOException {
+        this.seqid = xdr.xdrDecodeInt();
+        this.opaque = Opaque.forBytes(xdr.xdrDecodeOpaque(12));
     }
 
-    public stateid4(byte[] other, int seq) {
-        this.other = other;
-        seqid = seq;
+    public stateid4(byte[] bytes, int seqid) {
+        this(seqid, Opaque.forBytes(bytes));
     }
 
-    public stateid4(XdrDecodingStream xdr)
-            throws OncRpcException, IOException {
-        xdrDecode(xdr);
+    private stateid4(int seqid, Opaque other) {
+        this.seqid = seqid;
+        this.opaque = other.toImmutableOpaque();
+    }
+
+    public Opaque getOpaque() {
+        return opaque;
+    }
+
+    public int getSeqId() {
+        return seqid;
+    }
+
+    public long getClientId() {
+        return opaque.longAt(0);
+    }
+
+    public static long getClientId(Opaque stateIdOther) {
+        return stateIdOther.longAt(0);
+    }
+
+    public int getType() {
+        return opaque.byteAt(11);
+    }
+
+    public static int getType(Opaque stateIdOther) {
+        return stateIdOther.byteAt(11);
+    }
+
+    @Override
+    public stateid4 clone() {
+        return new stateid4(seqid, opaque);
     }
 
     public void xdrEncode(XdrEncodingStream xdr)
             throws OncRpcException, IOException {
         xdr.xdrEncodeInt(seqid);
-        xdr.xdrEncodeOpaque(other, 12);
+        xdr.xdrEncodeOpaque(opaque.toBytes(), 12);
     }
 
     public void xdrDecode(XdrDecodingStream xdr)
             throws OncRpcException, IOException {
         seqid = xdr.xdrDecodeInt();
-        other = xdr.xdrDecodeOpaque(12);
+        opaque = Opaque.forBytes(xdr.xdrDecodeOpaque(12));
     }
 
     @Override
@@ -72,7 +104,7 @@ public boolean equals(Object obj) {
 
         final stateid4 other_id = (stateid4) obj;
 
-        return Arrays.equals(this.other, other_id.other);
+        return this.opaque.equals(other_id.opaque);
     }
 
     /**
@@ -87,12 +119,12 @@ public boolean equalsWithSeq(stateid4 otherState) {
             return true;
         }
 
-        return otherState.seqid == this.seqid && Arrays.equals(this.other, otherState.other);
+        return otherState.seqid == this.seqid && this.opaque.equals(otherState.opaque);
     }
 
     @Override
     public int hashCode() {
-        return Arrays.hashCode(other);
+        return this.opaque.hashCode();
     }
 
     @Override
@@ -100,10 +132,28 @@ public String toString() {
         StringBuilder sb = new StringBuilder();
 
         sb.append("[");
-        sb.append(BaseEncoding.base16().lowerCase().encode(other));
+        sb.append(opaque);
         sb.append(", seq: ").append(seqid).append("]");
         return sb.toString();
     }
 
+    public void bumpSeqid() {
+        ++seqid;
+    }
+
+    private void writeObject(java.io.ObjectOutputStream out)
+            throws IOException {
+        PutField pf = out.putFields();
+        pf.put("seqid", this.seqid);
+        pf.put("other", this.opaque.toBytes());
+        out.writeFields();
+    }
+
+    private void readObject(java.io.ObjectInputStream in)
+            throws IOException, ClassNotFoundException {
+        GetField gf = in.readFields();
+        this.seqid = gf.get("seqid", 0);
+        this.opaque = Opaque.forBytes((byte[]) gf.get("other", new byte[0]));
+    }
 }
 // End of stateid4.java
diff --git a/core/src/main/java/org/dcache/nfs/vfs/ForwardingFileSystem.java b/core/src/main/java/org/dcache/nfs/vfs/ForwardingFileSystem.java
index c22e1108..00c1767b 100644
--- a/core/src/main/java/org/dcache/nfs/vfs/ForwardingFileSystem.java
+++ b/core/src/main/java/org/dcache/nfs/vfs/ForwardingFileSystem.java
@@ -26,6 +26,7 @@
 
 import javax.security.auth.Subject;
 
+import org.dcache.nfs.util.Opaque;
 import org.dcache.nfs.v4.NfsIdMapping;
 import org.dcache.nfs.v4.xdr.nfsace4;
 import org.dcache.nfs.vfs.Stat.StatAttribute;
@@ -107,8 +108,8 @@ public int read(Inode inode, ByteBuffer data, long offset) throws IOException {
     }
 
     @Override
-    public int read(Inode inode, ByteBuffer data, long offset, Runnable eofReached) throws IOException {
-        return delegate().read(inode, data, offset, eofReached);
+    public int read(Opaque stateId, Inode inode, ByteBuffer data, long offset, Runnable eofReached) throws IOException {
+        return delegate().read(stateId, inode, data, offset, eofReached);
     }
 
     @Override
@@ -138,11 +139,22 @@ public WriteResult write(Inode inode, ByteBuffer data, long offset, StabilityLev
         return delegate().write(inode, data, offset, stabilityLevel);
     }
 
+    @Override
+    public WriteResult write(Opaque stateId, Inode inode, ByteBuffer data, long offset, StabilityLevel stabilityLevel)
+            throws IOException {
+        return delegate().write(stateId, inode, data, offset, stabilityLevel);
+    }
+
     @Override
     public void commit(Inode inode, long offset, int count) throws IOException {
         delegate().commit(inode, offset, count);
     }
 
+    @Override
+    public void commit(Opaque stateId, Inode inode, long offset, int count) throws IOException {
+        delegate().commit(stateId, inode, offset, count);
+    }
+
     @Override
     public Stat getattr(Inode inode) throws IOException {
         return delegate().getattr(inode);
@@ -222,4 +234,14 @@ public void removeXattr(Inode inode, String attr) throws IOException {
     public CompletableFuture<Long> copyFileRange(Inode src, long srcPos, Inode dst, long dstPos, long len) {
         return delegate().copyFileRange(src, srcPos, dst, dstPos, len);
     }
+
+    @Override
+    public void open(Opaque stateId, Inode inode, OpenMode openMode) {
+        delegate().open(stateId, inode, openMode);
+    }
+
+    @Override
+    public void close(Opaque stateId) {
+        delegate().close(stateId);
+    }
 }
diff --git a/core/src/main/java/org/dcache/nfs/vfs/PseudoFs.java b/core/src/main/java/org/dcache/nfs/vfs/PseudoFs.java
index e5e26478..697e3f7f 100644
--- a/core/src/main/java/org/dcache/nfs/vfs/PseudoFs.java
+++ b/core/src/main/java/org/dcache/nfs/vfs/PseudoFs.java
@@ -71,10 +71,15 @@
 import org.dcache.nfs.status.NoEntException;
 import org.dcache.nfs.status.PermException;
 import org.dcache.nfs.status.RoFsException;
+import org.dcache.nfs.util.Opaque;
 import org.dcache.nfs.util.SubjectHolder;
+import org.dcache.nfs.v4.NFS4Client;
+import org.dcache.nfs.v4.NFSv4StateHandler;
 import org.dcache.nfs.v4.acl.Acls;
 import org.dcache.nfs.v4.xdr.acemask4;
+import org.dcache.nfs.v4.xdr.nfs4_prot;
 import org.dcache.nfs.v4.xdr.nfsace4;
+import org.dcache.nfs.v4.xdr.stateid4;
 import org.dcache.nfs.vfs.AclCheckable.Access;
 import org.dcache.nfs.vfs.Stat.StatAttribute;
 import org.dcache.oncrpc4j.rpc.RpcAuth;
@@ -105,6 +110,7 @@ public class PseudoFs extends ForwardingFileSystem {
     private final VirtualFileSystem _inner;
     private final ExportTable _exportTable;
     private final RpcAuth _auth;
+    private final NFSv4StateHandler _stateHandler;
 
     private final static int ACCESS4_MASK =
             ACCESS4_DELETE | ACCESS4_EXECUTE | ACCESS4_EXTEND
@@ -112,11 +118,16 @@ public class PseudoFs extends ForwardingFileSystem {
                     | ACCESS4_XAREAD | ACCESS4_XAWRITE | ACCESS4_XALIST;
 
     public PseudoFs(VirtualFileSystem inner, RpcCall call, ExportTable exportTable) {
+        this(inner, call, exportTable, null);
+    }
+
+    public PseudoFs(VirtualFileSystem inner, RpcCall call, ExportTable exportTable, NFSv4StateHandler stateHandler) {
         _inner = inner;
         _subject = call.getCredential().getSubject();
         _auth = call.getCredential();
         _inetAddress = call.getTransport().getRemoteSocketAddress();
         _exportTable = exportTable;
+        _stateHandler = stateHandler;
     }
 
     @Override
@@ -329,10 +340,29 @@ public int read(Inode inode, ByteBuffer data, long offset) throws IOException {
         return _inner.read(innerInode(inode), data, offset);
     }
 
+    private void checkAccessReadWriteData(Opaque stateId, Inode inode, boolean write) throws IOException {
+        if (_stateHandler != null) {
+            NFS4Client client = _stateHandler.getClientIfExists(stateid4.getClientId(stateId));
+            if (client != null) {
+                int shareAccess;
+                try {
+                    shareAccess = _stateHandler.getFileTracker().getShareAccess(client, inode, stateId);
+                    if ((shareAccess & (write ? nfs4_prot.OPEN4_SHARE_ACCESS_WRITE
+                            : nfs4_prot.OPEN4_SHARE_ACCESS_READ)) != 0) {
+                        return; // permit
+                    }
+                } catch (ChimeraNFSException e) {
+                    // ignore; check below and throw proper exception
+                }
+            }
+        }
+        checkAccess(inode, write ? ACE4_WRITE_DATA : ACE4_READ_DATA);
+    }
+
     @Override
-    public int read(Inode inode, ByteBuffer data, long offset, Runnable eofReached) throws IOException {
-        checkAccess(inode, ACE4_READ_DATA);
-        return _inner.read(innerInode(inode), data, offset, eofReached);
+    public int read(Opaque stateId, Inode inode, ByteBuffer data, long offset, Runnable eofReached) throws IOException {
+        checkAccessReadWriteData(stateId, inode, false);
+        return _inner.read(stateId, innerInode(inode), data, offset, eofReached);
     }
 
     @Override
@@ -383,6 +413,13 @@ public WriteResult write(Inode inode, ByteBuffer data, long offset, StabilityLev
         return _inner.write(innerInode(inode), data, offset, stabilityLevel);
     }
 
+    @Override
+    public WriteResult write(Opaque stateId, Inode inode, ByteBuffer data, long offset, StabilityLevel stabilityLevel)
+            throws IOException {
+        checkAccessReadWriteData(stateId, inode, true);
+        return _inner.write(stateId, innerInode(inode), data, offset, stabilityLevel);
+    }
+
     @Override
     public Stat getattr(Inode inode) throws IOException {
         checkAccess(inode, ACE4_READ_ATTRIBUTES);
diff --git a/core/src/main/java/org/dcache/nfs/vfs/VirtualFileSystem.java b/core/src/main/java/org/dcache/nfs/vfs/VirtualFileSystem.java
index fd1e778d..229e1880 100644
--- a/core/src/main/java/org/dcache/nfs/vfs/VirtualFileSystem.java
+++ b/core/src/main/java/org/dcache/nfs/vfs/VirtualFileSystem.java
@@ -29,6 +29,7 @@
 import org.dcache.nfs.status.InvalException;
 import org.dcache.nfs.status.IsDirException;
 import org.dcache.nfs.status.NotSuppException;
+import org.dcache.nfs.util.Opaque;
 import org.dcache.nfs.v4.NfsIdMapping;
 import org.dcache.nfs.v4.xdr.nfsace4;
 import org.dcache.nfs.v4.xdr.stable_how4;
@@ -226,6 +227,7 @@ default int read(Inode inode, ByteBuffer data, long offset) throws IOException {
      * information via {@link #getattr(Inode)}), which may incur a higher, recurring cost than the inconvenience of a
      * single additional client roundtrip at the end of the file.
      *
+     * @param stateId The stateId as obtained via an {@code open} command via NFSv4, or {@code null}.
      * @param inode inode of the file to read from.
      * @param data byte array for writing.
      * @param offset file's position to read from.
@@ -234,7 +236,8 @@ default int read(Inode inode, ByteBuffer data, long offset) throws IOException {
      * @return number of bytes read from the file, possibly zero. -1 if EOF is reached.
      * @throws IOException
      */
-    default int read(Inode inode, ByteBuffer data, long offset, Runnable eofReached) throws IOException {
+    default int read(Opaque stateId, Inode inode, ByteBuffer data, long offset, Runnable eofReached)
+            throws IOException {
         Stat stat = getattr(inode);
 
         Stat.Type statType = stat.type();
@@ -317,6 +320,22 @@ default WriteResult write(Inode inode, ByteBuffer data, long offset, StabilityLe
         return write(inode, bytes, offset, count, stabilityLevel);
     }
 
+    /**
+     * Write provided {@code data} into inode with a given stability level.
+     *
+     * @param stateId The stateId as obtained via an {@code open} command via NFSv4, or {@code null}.
+     * @param inode inode of the file to write.
+     * @param data data to be written.
+     * @param offset the file position to begin writing at.
+     * @param stabilityLevel data stability level.
+     * @return write result.
+     * @throws IOException
+     */
+    default WriteResult write(Opaque stateId, Inode inode, ByteBuffer data, long offset, StabilityLevel stabilityLevel)
+            throws IOException {
+        return write(inode, data, offset, stabilityLevel);
+    }
+
     /**
      * Flush data in {@code dirty} state to the stable storage. Typically follows
      * {@link #write(Inode, ByteBuffer, long, StabilityLevel)} operation.
@@ -328,6 +347,20 @@ default WriteResult write(Inode inode, ByteBuffer data, long offset, StabilityLe
      */
     void commit(Inode inode, long offset, int count) throws IOException;
 
+    /**
+     * Flush data in {@code dirty} state to the stable storage. Typically follows
+     * {@link #write(Inode, ByteBuffer, long, StabilityLevel)} operation.
+     *
+     * @param stateId The stateId as obtained via an {@code open} command via NFSv4, or {@code null}.
+     * @param inode inode of the file to commit.
+     * @param offset the file position to start commit at.
+     * @param count number of bytes to commit.
+     * @throws IOException
+     */
+    default void commit(Opaque stateId, Inode inode, long offset, int count) throws IOException {
+        commit(inode, offset, count);
+    }
+
     /**
      * Get file system object's attributes.
      *
@@ -444,6 +477,18 @@ public StabilityLevel getStabilityLevel() {
         }
     }
 
+    enum OpenMode {
+        READ_ONLY, WRITE_ONLY, READ_WRITE;
+
+        boolean canRead() {
+            return this == READ_ONLY || this == READ_WRITE;
+        }
+
+        boolean canWrite() {
+            return this == WRITE_ONLY || this == READ_WRITE;
+        }
+    }
+
     // NOTE - stability values and ordinals are the same for nfs 3 and 4
     /**
      * Write stability level.
@@ -588,4 +633,25 @@ default CompletableFuture<Long> copyFileRange(Inode src, long srcPos, Inode dst,
     default Inode inodeForNfsHandle(byte[] bytes) throws IOException {
         return Inode.forNfsHandle(bytes);
     }
+
+    /**
+     * Notifies the filing system about an explicit open operation to an {@link Inode}, using the given open mode and
+     * the specified stateId as a reference for {@link #read(Opaque, Inode, ByteBuffer, long, Runnable)},
+     * {@link #write(Opaque, Inode, ByteBuffer, long, StabilityLevel)} and {@link #commit(Opaque, Inode, long, int)}.
+     * 
+     * @param stateId The stateId.
+     * @param inode The {@link Inode}.
+     * @param openMode The open mode.
+     */
+    default void open(Opaque stateId, Inode inode, OpenMode openMode) {
+    }
+
+    /**
+     * Notifies the filing system about an explicit close operation corresponding to the given stateId.
+     * 
+     * @param stateId The stateId.
+     * @see #open(Opaque, Inode, OpenMode)
+     */
+    default void close(Opaque stateId) {
+    }
 }
diff --git a/core/src/test/java/org/dcache/nfs/v4/OperationREADTest.java b/core/src/test/java/org/dcache/nfs/v4/OperationREADTest.java
index 7d4f47fd..5c8cd101 100644
--- a/core/src/test/java/org/dcache/nfs/v4/OperationREADTest.java
+++ b/core/src/test/java/org/dcache/nfs/v4/OperationREADTest.java
@@ -54,7 +54,7 @@ public void testLeaseUpdateForV40Client() throws UnknownHostException, ChimeraNF
         FileTracker fileTracker = mock(FileTracker.class);
 
         when(stateHandler.getFileTracker()).thenReturn(fileTracker);
-        when(fileTracker.getShareAccess(any(), any(), any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_READ);
+        when(fileTracker.getShareAccess(any(), any(), (stateid4) any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_READ);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
         when(session.getClient()).thenReturn(client);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
@@ -90,7 +90,7 @@ public void testNoLeaseUpdateForV41Client() throws UnknownHostException, Chimera
         FileTracker fileTracker = mock(FileTracker.class);
 
         when(stateHandler.getFileTracker()).thenReturn(fileTracker);
-        when(fileTracker.getShareAccess(any(), any(), any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_READ);
+        when(fileTracker.getShareAccess(any(), any(), (stateid4) any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_READ);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
         when(session.getClient()).thenReturn(client);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
diff --git a/core/src/test/java/org/dcache/nfs/v4/OperationWRITETest.java b/core/src/test/java/org/dcache/nfs/v4/OperationWRITETest.java
index b02bfa48..90d07b77 100644
--- a/core/src/test/java/org/dcache/nfs/v4/OperationWRITETest.java
+++ b/core/src/test/java/org/dcache/nfs/v4/OperationWRITETest.java
@@ -57,14 +57,14 @@ public void testLeaseUpdateForV40Client() throws UnknownHostException, ChimeraNF
         FileTracker fileTracker = mock(FileTracker.class);
 
         when(stateHandler.getFileTracker()).thenReturn(fileTracker);
-        when(fileTracker.getShareAccess(any(), any(), any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_WRITE);
+        when(fileTracker.getShareAccess(any(), any(), (stateid4) any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_WRITE);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
         when(session.getClient()).thenReturn(client);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
 
         when(vfs.getattr(any())).thenReturn(fileStat);
         when(vfs.getattr(any(), any())).thenCallRealMethod();
-        when(vfs.write(any(), any(), anyLong(), any()))
+        when(vfs.write(any(), any(), any(), anyLong(), any()))
                 .thenReturn(new VirtualFileSystem.WriteResult(VirtualFileSystem.StabilityLevel.UNSTABLE, 1));
 
         COMPOUND4args writeArgs = new CompoundBuilder()
@@ -94,14 +94,14 @@ public void testNoLeaseUpdateForV41Client() throws UnknownHostException, Chimera
         FileTracker fileTracker = mock(FileTracker.class);
 
         when(stateHandler.getFileTracker()).thenReturn(fileTracker);
-        when(fileTracker.getShareAccess(any(), any(), any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_WRITE);
+        when(fileTracker.getShareAccess(any(), any(), (stateid4) any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_WRITE);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
         when(session.getClient()).thenReturn(client);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
 
         when(vfs.getattr(any())).thenReturn(fileStat);
         when(vfs.getattr(any(), any())).thenCallRealMethod();
-        when(vfs.write(any(), any(), anyLong(), any()))
+        when(vfs.write(any(), any(), any(), anyLong(), any()))
                 .thenReturn(new VirtualFileSystem.WriteResult(VirtualFileSystem.StabilityLevel.UNSTABLE, 1));
 
         COMPOUND4args writeArgs = new CompoundBuilder()
@@ -131,7 +131,7 @@ public void testReturnWriteVerifier() throws UnknownHostException, ChimeraNFSExc
         FileTracker fileTracker = mock(FileTracker.class);
 
         when(stateHandler.getFileTracker()).thenReturn(fileTracker);
-        when(fileTracker.getShareAccess(any(), any(), any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_WRITE);
+        when(fileTracker.getShareAccess(any(), any(), (stateid4) any())).thenReturn(nfs4_prot.OPEN4_SHARE_ACCESS_WRITE);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
         when(session.getClient()).thenReturn(client);
         when(stateHandler.getClientIdByStateId(any())).thenReturn(client);
@@ -140,7 +140,7 @@ public void testReturnWriteVerifier() throws UnknownHostException, ChimeraNFSExc
 
         when(vfs.getattr(any())).thenReturn(fileStat);
         when(vfs.getattr(any(), any())).thenCallRealMethod();
-        when(vfs.write(any(), any(), anyLong(), any()))
+        when(vfs.write(any(), any(), any(), anyLong(), any()))
                 .thenReturn(new VirtualFileSystem.WriteResult(VirtualFileSystem.StabilityLevel.UNSTABLE, 1));
 
         COMPOUND4args writeArgs = new CompoundBuilder()
diff --git a/core/src/test/java/org/dcache/nfs/v4/xdr/stateid4Test.java b/core/src/test/java/org/dcache/nfs/v4/xdr/stateid4Test.java
index 61e0bd05..b8989e3f 100644
--- a/core/src/test/java/org/dcache/nfs/v4/xdr/stateid4Test.java
+++ b/core/src/test/java/org/dcache/nfs/v4/xdr/stateid4Test.java
@@ -21,8 +21,6 @@
 
 import static org.junit.Assert.*;
 
-import org.dcache.nfs.v4.xdr.stateid4;
-import org.dcache.nfs.v4.xdr.uint32_t;
 import org.junit.Test;
 
 public class stateid4Test {
@@ -30,13 +28,9 @@ public class stateid4Test {
     @Test
     public void testEqualsTrue() {
 
-        stateid4 stateidA = new stateid4();
-        stateidA.seqid = 1;
-        stateidA.other = "state".getBytes();
+        stateid4 stateidA = new stateid4("state".getBytes(), 1);
 
-        stateid4 stateidB = new stateid4();
-        stateidB.seqid = 1;
-        stateidB.other = "state".getBytes();
+        stateid4 stateidB = new stateid4("state".getBytes(), 1);
 
         assertTrue("equal keys not equal", stateidA.equals(stateidB));
         assertTrue("equal, but different hashCode", stateidA.hashCode() == stateidB.hashCode());
@@ -46,9 +40,7 @@ public void testEqualsTrue() {
     @Test
     public void testEqualsSame() {
 
-        stateid4 stateidA = new stateid4();
-        stateidA.seqid = 1;
-        stateidA.other = "state".getBytes();
+        stateid4 stateidA = new stateid4("state".getBytes(), 1);
 
         assertTrue("equal keys not equal", stateidA.equals(stateidA));
     }
@@ -56,13 +48,9 @@ public void testEqualsSame() {
     @Test
     public void testDifferSequence() {
 
-        stateid4 stateidA = new stateid4();
-        stateidA.seqid = 1;
-        stateidA.other = "state".getBytes();
+        stateid4 stateidA = new stateid4("state".getBytes(), 1);
 
-        stateid4 stateidB = new stateid4();
-        stateidB.seqid = 2;
-        stateidB.other = "state".getBytes();
+        stateid4 stateidB = new stateid4("state".getBytes(), 2);
 
         assertTrue("differ by sequence should still be equal", stateidA.equals(stateidB));
         assertFalse("differ by sequence can't be equal", stateidA.equalsWithSeq(stateidB));
@@ -71,13 +59,9 @@ public void testDifferSequence() {
     @Test
     public void testDifferOther() {
 
-        stateid4 stateidA = new stateid4();
-        stateidA.seqid = 1;
-        stateidA.other = "stateA".getBytes();
+        stateid4 stateidA = new stateid4("stateA".getBytes(), 1);
 
-        stateid4 stateidB = new stateid4();
-        stateidB.seqid = 1;
-        stateidB.other = "stateB".getBytes();
+        stateid4 stateidB = new stateid4("stateB".getBytes(), 1);
 
         assertFalse("differ by other not detected", stateidA.equals(stateidB));
     }