diff --git a/genode/dagfs_genode/dagfs_genode.nimble b/genode/dagfs_genode/dagfs_genode.nimble
index 5215ef5..041ee14 100644
--- a/genode/dagfs_genode/dagfs_genode.nimble
+++ b/genode/dagfs_genode/dagfs_genode.nimble
@@ -20,4 +20,4 @@ backend       = "cpp"
 requires "nim >= 0.18.1", "dagfs", "genode"
 
 task genode, "Build for Genode":
-  exec "nimble build --os:genode -d:posix -d:tcpdebug"
+  exec "nimble build --os:genode -d:posix"
diff --git a/genode/dagfs_genode/src/dagfs_client.nim b/genode/dagfs_genode/src/dagfs_client.nim
index fc6d514..64f0317 100644
--- a/genode/dagfs_genode/src/dagfs_client.nim
+++ b/genode/dagfs_genode/src/dagfs_client.nim
@@ -119,7 +119,7 @@ proc fendGetBuffer(s: DagfsStore; cid: Cid; buf: pointer; len: Natural): int =
     let pktBuf = fend.cpp.packetContent ack
     assert(not pktBuf.isNil, "ack packet has nil content")
     assert(ack.len <= len)
-    assert(ack.len > 0)
+    assert(0 < ack.len)
     result = ack.len
     copyMem(buf, pktBuf, result)
   if pkt.size > 0:
@@ -189,12 +189,13 @@ proc newDagfsBackend*(env: GenodeEnv; store: DagfsStore; label = ""; bufferSize
       let
         buf = bend.cpp.packetContent(pkt)
         cid = pkt.cid
-      case pkt.operation
+      case pkt.op
       of GET:
+        pkt.setOp(PUT)
         try:
           let n = store.getBuffer(cid, buf, pkt.size)
           pkt.setLen(n)
-          bend.cpp.submitPacket(pkt, cid.toHex, PUT)
+          bend.cpp.submitPacket(pkt)
         except MissingChunk:
           pkt.setError(MISSING)
           bend.cpp.submitPacket(pkt)
diff --git a/genode/dagfs_genode/src/dagfs_server.nim b/genode/dagfs_genode/src/dagfs_server.nim
index 27fecac..7d6e97a 100644
--- a/genode/dagfs_genode/src/dagfs_server.nim
+++ b/genode/dagfs_genode/src/dagfs_server.nim
@@ -94,7 +94,7 @@ proc isPending(fend: Frontend; cid: Cid): bool =
 proc isPending(fend: Session; cid: Cid; op: DagfsOpcode): bool =
   if fend.cpp.packetAvail and fend.cpp.readyToAck:
     let pkt = fend.cpp.peekPacket()
-    result = (pkt.operation == op and cid == pkt.cid)
+    result = (pkt.op == op and cid == pkt.cid)
 
 proc processPacket(backends: Backends; fend: Frontend): bool =
   if backends.len < 1:
@@ -106,7 +106,7 @@ proc processPacket(backends: Backends; fend: Frontend): bool =
   let
     pkt = fend.cpp.peekPacket
     cid = pkt.cid
-    op = pkt.operation
+    op = pkt.op
   case op
   of GET:
     for bend in backends.values:
@@ -129,13 +129,13 @@ proc processPacket(frontends: Frontends; bend: Backend): bool =
   let
     pkt = bend.cpp.getPacket
     cid = pkt.cid
-    op = pkt.operation
+    op = pkt.op
   case op
   of PUT:
-    assert(0 < pkt.len)
     for fend in frontends.values:
       if fend.isPending(cid, GET):
         var ack = fend.cpp.getPacket
+        ack.setError(pkt.error)
         if ack.size < pkt.len:
           ack.setError(OVERSIZE)
           fend.cpp.acknowledgePacket(ack)
@@ -148,7 +148,7 @@ proc processPacket(frontends: Frontends; bend: Backend): bool =
       if fend.isPending(cid, PUT):
         fend.cpp.acknowledgePacket(fend.cpp.getPacket, cid, IDLE)
   else:
-    echo "invalid backend packet operation from ", bend.label
+    echo "invalid ", op, " packet from backend ", bend.label
   bend.idle.addLast pkt
   true
 
diff --git a/genode/dagfs_genode/src/dagfs_session.nim b/genode/dagfs_genode/src/dagfs_session.nim
index f112144..88e0c17 100644
--- a/genode/dagfs_genode/src/dagfs_session.nim
+++ b/genode/dagfs_genode/src/dagfs_session.nim
@@ -38,7 +38,12 @@ proc cid*(p: DagfsPacket): Cid = parseCid $p.cidStr
 proc setCid*(p: var DagfsPacket; cid: cstring) {.importcpp: "#.cid(@)".}
 proc setCid*(p: var DagfsPacket; cid: Cid) = p.setCid(cid.toHex())
 
-proc operation*(pkt: DagfsPacket): DagfsOpcode {.importcpp.}
+
+
+proc op*(pkt: DagfsPacket): DagfsOpcode {.importcpp.}
+
+proc setOp*(p: var DagfsPacket; op: DagfsOpcode) {.importcpp: "op".}
+
 proc len*(pkt: DagfsPacket): csize {.importcpp: "length".}
   ## Logical packet length.
 proc setLen*(pkt: var DagfsPacket; len: int) {.importcpp: "length".}
diff --git a/genode/include/dagfs_session/dagfs_session.h b/genode/include/dagfs_session/dagfs_session.h
index 1433ac3..9a3670f 100644
--- a/genode/include/dagfs_session/dagfs_session.h
+++ b/genode/include/dagfs_session/dagfs_session.h
@@ -71,13 +71,14 @@ struct Dagfs::Packet final : Genode::Packet_descriptor
 	{ }
 
 	Cid   const &cid() const { return _cid;    }
-	Opcode operation() const { return _op;     }
+	Opcode        op() const { return _op;     }
 	size_t    length() const { return _length; }
 	Error      error() const { return _err;    }
 
 	void cid(char const *hex)  { _cid = Cid(hex); }
+	void       op(Opcode o) {     _op = o;   }
 	void length(size_t len) { _length = len; }
-	void  error(Error err)  {    _err = err; }
+	void   error(Error err) {    _err = err; }
 };
 
 
diff --git a/src/dagfs/stores.nim b/src/dagfs/stores.nim
index 386e5c6..6dcdb02 100644
--- a/src/dagfs/stores.nim
+++ b/src/dagfs/stores.nim
@@ -44,7 +44,7 @@ proc getBuffer*(s: DagfsStore; cid: Cid; buf: pointer; len: Natural): int =
   assert(0 < len)
   assert(not s.getBufferImpl.isNil)
   result = s.getBufferImpl(s, cid, buf, len)
-  assert(result > 0)
+  assert(0 < result)
 
 proc get*(s: DagfsStore; cid: Cid; result: var string) =
   ## Retrieve a raw block from the store.