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// Copyright 2021 The gVisor Authors.
//
// 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.
//go:build linux
// +build linux
package sharedmem
import (
"fmt"
"io/ioutil"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/eventfd"
)
const (
// defaultQueueDataSize is the size of the shared memory data region that
// holds the scatter/gather buffers.
defaultQueueDataSize = 1 << 20 // 1MiB
// defaultQueuePipeSize is the size of the pipe that holds the packet descriptors.
//
// Assuming each packet data is approximately 1280 bytes (IPv6 Minimum MTU)
// then we can hold approximately 1024*1024/1280 ~ 819 packets in the data
// area. Which means the pipe needs to be big enough to hold 819
// descriptors.
//
// Each descriptor is approximately 8 (slot descriptor in pipe) +
// 16 (packet descriptor) + 12 (for buffer descriptor) assuming each packet is
// stored in exactly 1 buffer descriptor (see queue/tx.go and pipe/tx.go.)
//
// Which means we need approximately 36*819 ~ 29 KiB to store all packet
// descriptors. We could go with a 32 KiB pipe but to give it some slack in
// how the upper layer may make use of the scatter gather buffers we double
// this to hold enough descriptors.
defaultQueuePipeSize = 64 << 10 // 64KiB
// defaultSharedDataSize is the size of the sharedData region used to
// enable/disable notifications.
defaultSharedDataSize = 4 << 10 // 4KiB
)
// A QueuePair represents a pair of TX/RX queues.
type QueuePair struct {
// txCfg is the QueueConfig to be used for transmit queue.
txCfg QueueConfig
// rxCfg is the QueueConfig to be used for receive queue.
rxCfg QueueConfig
}
// NewQueuePair creates a shared memory QueuePair.
func NewQueuePair() (*QueuePair, error) {
txCfg, err := createQueueFDs(queueSizes{
dataSize: defaultQueueDataSize,
txPipeSize: defaultQueuePipeSize,
rxPipeSize: defaultQueuePipeSize,
sharedDataSize: defaultSharedDataSize,
})
if err != nil {
return nil, fmt.Errorf("failed to create tx queue: %s", err)
}
rxCfg, err := createQueueFDs(queueSizes{
dataSize: defaultQueueDataSize,
txPipeSize: defaultQueuePipeSize,
rxPipeSize: defaultQueuePipeSize,
sharedDataSize: defaultSharedDataSize,
})
if err != nil {
closeFDs(txCfg)
return nil, fmt.Errorf("failed to create rx queue: %s", err)
}
return &QueuePair{
txCfg: txCfg,
rxCfg: rxCfg,
}, nil
}
// Close closes underlying tx/rx queue fds.
func (q *QueuePair) Close() {
closeFDs(q.txCfg)
closeFDs(q.rxCfg)
}
// TXQueueConfig returns the QueueConfig for the receive queue.
func (q *QueuePair) TXQueueConfig() QueueConfig {
return q.txCfg
}
// RXQueueConfig returns the QueueConfig for the transmit queue.
func (q *QueuePair) RXQueueConfig() QueueConfig {
return q.rxCfg
}
type queueSizes struct {
dataSize int64
txPipeSize int64
rxPipeSize int64
sharedDataSize int64
}
func createQueueFDs(s queueSizes) (QueueConfig, error) {
success := false
var eventFD eventfd.Eventfd
var dataFD, txPipeFD, rxPipeFD, sharedDataFD int
defer func() {
if success {
return
}
closeFDs(QueueConfig{
EventFD: eventFD,
DataFD: dataFD,
TxPipeFD: txPipeFD,
RxPipeFD: rxPipeFD,
SharedDataFD: sharedDataFD,
})
}()
eventFD, err := eventfd.Create()
if err != nil {
return QueueConfig{}, fmt.Errorf("eventfd failed: %v", err)
}
dataFD, err = createFile(s.dataSize, false)
if err != nil {
return QueueConfig{}, fmt.Errorf("failed to create dataFD: %s", err)
}
txPipeFD, err = createFile(s.txPipeSize, true)
if err != nil {
return QueueConfig{}, fmt.Errorf("failed to create txPipeFD: %s", err)
}
rxPipeFD, err = createFile(s.rxPipeSize, true)
if err != nil {
return QueueConfig{}, fmt.Errorf("failed to create rxPipeFD: %s", err)
}
sharedDataFD, err = createFile(s.sharedDataSize, false)
if err != nil {
return QueueConfig{}, fmt.Errorf("failed to create sharedDataFD: %s", err)
}
success = true
return QueueConfig{
EventFD: eventFD,
DataFD: dataFD,
TxPipeFD: txPipeFD,
RxPipeFD: rxPipeFD,
SharedDataFD: sharedDataFD,
}, nil
}
func createFile(size int64, initQueue bool) (fd int, err error) {
const tmpDir = "/dev/shm/"
f, err := ioutil.TempFile(tmpDir, "sharedmem_test")
if err != nil {
return -1, fmt.Errorf("TempFile failed: %v", err)
}
defer f.Close()
unix.Unlink(f.Name())
if initQueue {
// Write the "slot-free" flag in the initial queue.
if _, err := f.WriteAt([]byte{0, 0, 0, 0, 0, 0, 0, 0x80}, 0); err != nil {
return -1, fmt.Errorf("WriteAt failed: %v", err)
}
}
fd, err = unix.Dup(int(f.Fd()))
if err != nil {
return -1, fmt.Errorf("unix.Dup(%d) failed: %v", f.Fd(), err)
}
if err := unix.Ftruncate(fd, size); err != nil {
unix.Close(fd)
return -1, fmt.Errorf("ftruncate(%d, %d) failed: %v", fd, size, err)
}
return fd, nil
}
func closeFDs(c QueueConfig) {
unix.Close(c.DataFD)
c.EventFD.Close()
unix.Close(c.TxPipeFD)
unix.Close(c.RxPipeFD)
unix.Close(c.SharedDataFD)
}
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