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