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// Copyright 2016 The Netstack Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package queue
import (
"encoding/binary"
"gvisor.googlesource.com/gvisor/pkg/log"
"gvisor.googlesource.com/gvisor/pkg/tcpip/link/sharedmem/pipe"
)
const (
// Offsets within a packet header.
packetID = 0
packetSize = 8
packetReserved = 12
sizeOfPacketHeader = 16
// Offsets with a buffer descriptor
bufferOffset = 0
bufferSize = 8
sizeOfBufferDescriptor = 12
)
// TxBuffer is the descriptor of a transmit buffer.
type TxBuffer struct {
Next *TxBuffer
Offset uint64
Size uint32
}
// Tx is a transmit queue. It is implemented with one tx and one rx pipe: the
// tx pipe is used to request the transmission of packets, while the rx pipe
// is used to receive which transmissions have completed.
//
// This struct is thread-compatible.
type Tx struct {
tx pipe.Tx
rx pipe.Rx
}
// Init initializes the transmit queue with the given pipes.
func (t *Tx) Init(tx, rx []byte) {
t.tx.Init(tx)
t.rx.Init(rx)
}
// Enqueue queues the given linked list of buffers for transmission as one
// packet. While it is queued, the caller must not modify them.
func (t *Tx) Enqueue(id uint64, totalDataLen, bufferCount uint32, buffer *TxBuffer) bool {
// Reserve room in the tx pipe.
totalLen := sizeOfPacketHeader + uint64(bufferCount)*sizeOfBufferDescriptor
b := t.tx.Push(totalLen)
if b == nil {
return false
}
// Initialize the packet and buffer descriptors.
binary.LittleEndian.PutUint64(b[packetID:], id)
binary.LittleEndian.PutUint32(b[packetSize:], totalDataLen)
binary.LittleEndian.PutUint32(b[packetReserved:], 0)
offset := sizeOfPacketHeader
for i := bufferCount; i != 0; i-- {
binary.LittleEndian.PutUint64(b[offset+bufferOffset:], buffer.Offset)
binary.LittleEndian.PutUint32(b[offset+bufferSize:], buffer.Size)
offset += sizeOfBufferDescriptor
buffer = buffer.Next
}
t.tx.Flush()
return true
}
// CompletedPacket returns the id of the last completed transmission. The
// returned id, if any, refers to a value passed on a previous call to
// Enqueue().
func (t *Tx) CompletedPacket() (id uint64, ok bool) {
for {
b := t.rx.Pull()
if b == nil {
return 0, false
}
if len(b) != 8 {
t.rx.Flush()
log.Warningf("Ignoring completed packet: size (%v) is less than expected (%v)", len(b), 8)
continue
}
v := binary.LittleEndian.Uint64(b)
t.rx.Flush()
return v, true
}
}
// Bytes returns the byte slices on which the queue operates.
func (t *Tx) Bytes() (tx, rx []byte) {
return t.tx.Bytes(), t.rx.Bytes()
}
// TxPacketInfo holds information about a packet sent on a tx queue.
type TxPacketInfo struct {
ID uint64
Size uint32
Reserved uint32
BufferCount int
}
// DecodeTxPacketHeader decodes the header of a packet sent over a tx queue.
func DecodeTxPacketHeader(b []byte) TxPacketInfo {
return TxPacketInfo{
ID: binary.LittleEndian.Uint64(b[packetID:]),
Size: binary.LittleEndian.Uint32(b[packetSize:]),
Reserved: binary.LittleEndian.Uint32(b[packetReserved:]),
BufferCount: (len(b) - sizeOfPacketHeader) / sizeOfBufferDescriptor,
}
}
// DecodeTxBufferHeader decodes the header of the i-th buffer of a packet sent
// over a tx queue.
func DecodeTxBufferHeader(b []byte, i int) TxBuffer {
b = b[sizeOfPacketHeader+i*sizeOfBufferDescriptor:]
return TxBuffer{
Offset: binary.LittleEndian.Uint64(b[bufferOffset:]),
Size: binary.LittleEndian.Uint32(b[bufferSize:]),
}
}
// EncodeTxCompletion encodes a tx completion header.
func EncodeTxCompletion(b []byte, id uint64) {
binary.LittleEndian.PutUint64(b, id)
}
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