gomemif: introduce gomemif

golang native memif driver

Type: feature

Signed-off-by: Jakub Grajciar <jgrajcia@cisco.com>
Change-Id: I693156a44011c80025245d25134f5bf5db6eba82
Signed-off-by: Jakub Grajciar <jgrajcia@cisco.com>

extras/gomemif/memif/packet_reader.go

@@ -0,0 +1,91 @@
+/*
+ *------------------------------------------------------------------
+ * Copyright (c) 2020 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *------------------------------------------------------------------
+ */
+
+package memif
+
+import "fmt"
+
+// ReadPacket reads one packet form the shared memory and
+// returns the number of bytes read
+func (q *Queue) ReadPacket(pkt []byte) (int, error) {
+	var mask int = q.ring.size - 1
+	var slot int
+	var lastSlot int
+	var length int
+	var offset int
+	var pktOffset int = 0
+	var nSlots uint16
+	var desc descBuf = newDescBuf()
+
+	if q.i.args.IsMaster {
+		slot = int(q.lastHead)
+		lastSlot = q.readHead()
+	} else {
+		slot = int(q.lastTail)
+		lastSlot = q.readTail()
+	}
+
+	nSlots = uint16(lastSlot - slot)
+	if nSlots == 0 {
+		goto refill
+	}
+
+	// copy descriptor from shm
+	q.getDescBuf(slot&mask, desc)
+	length = desc.getLength()
+	offset = desc.getOffset()
+
+	copy(pkt[:], q.i.regions[desc.getRegion()].data[offset:offset+length])
+	pktOffset += length
+
+	slot++
+	nSlots--
+
+	for (desc.getFlags() & descFlagNext) == descFlagNext {
+		if nSlots == 0 {
+			return 0, fmt.Errorf("Incomplete chained buffer, may suggest peer error.")
+		}
+
+		q.getDescBuf(slot&mask, desc)
+		length = desc.getLength()
+		offset = desc.getOffset()
+
+		copy(pkt[pktOffset:], q.i.regions[desc.getRegion()].data[offset:offset+length])
+		pktOffset += length
+
+		slot++
+		nSlots--
+	}
+
+refill:
+	if q.i.args.IsMaster {
+		q.lastHead = uint16(slot)
+		q.writeTail(slot)
+	} else {
+		q.lastTail = uint16(slot)
+
+		head := q.readHead()
+
+		for nSlots := uint16(q.ring.size - head + int(q.lastTail)); nSlots > 0; nSlots-- {
+			q.setDescLength(head&mask, int(q.i.run.PacketBufferSize))
+			head++
+		}
+		q.writeHead(head)
+	}
+
+	return pktOffset, nil
+}