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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 (
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/atomicbitops"
"gvisor.dev/gvisor/pkg/buffer"
"gvisor.dev/gvisor/pkg/cleanup"
"gvisor.dev/gvisor/pkg/eventfd"
"gvisor.dev/gvisor/pkg/tcpip/link/sharedmem/pipe"
"gvisor.dev/gvisor/pkg/tcpip/link/sharedmem/queue"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
// serverTx represents the server end of the sharedmem queue and is used to send
// packets to the peer in the buffers posted by the peer in the fillPipe.
type serverTx struct {
// fillPipe represents the receive end of the pipe that carries the RxBuffers
// posted by the peer.
fillPipe pipe.Rx
// completionPipe represents the transmit end of the pipe that carries the
// descriptors for filled RxBuffers.
completionPipe pipe.Tx
// data represents the buffer area where the packet payload is held.
data []byte
// eventFD is used to notify the peer when fill requests are fulfilled.
eventFD eventfd.Eventfd
// sharedData the memory region to use to enable/disable notifications.
sharedData []byte
// sharedEventFDState is the memory region in sharedData used to enable/disable
// notifications on eventFD.
sharedEventFDState *atomicbitops.Uint32
}
// init initializes all tstate needed by the serverTx queue based on the
// information provided.
//
// The caller always retains ownership of all file descriptors passed in. The
// queue implementation will duplicate any that it may need in the future.
func (s *serverTx) init(c *QueueConfig) error {
// Map in all buffers.
fillPipeMem, err := getBuffer(c.TxPipeFD)
if err != nil {
return err
}
cu := cleanup.Make(func() { unix.Munmap(fillPipeMem) })
defer cu.Clean()
completionPipeMem, err := getBuffer(c.RxPipeFD)
if err != nil {
return err
}
cu.Add(func() { unix.Munmap(completionPipeMem) })
data, err := getBuffer(c.DataFD)
if err != nil {
return err
}
cu.Add(func() { unix.Munmap(data) })
sharedData, err := getBuffer(c.SharedDataFD)
if err != nil {
return err
}
cu.Add(func() { unix.Munmap(sharedData) })
// Duplicate the eventFD so that caller can close it but we can still
// use it.
efd, err := c.EventFD.Dup()
if err != nil {
return err
}
cu.Add(func() { efd.Close() })
cu.Release()
s.fillPipe.Init(fillPipeMem)
s.completionPipe.Init(completionPipeMem)
s.data = data
s.eventFD = efd
s.sharedData = sharedData
s.sharedEventFDState = sharedDataPointer(sharedData)
return nil
}
func (s *serverTx) cleanup() {
unix.Munmap(s.fillPipe.Bytes())
unix.Munmap(s.completionPipe.Bytes())
unix.Munmap(s.data)
unix.Munmap(s.sharedData)
s.eventFD.Close()
}
// acquireBuffers acquires enough buffers to hold all the data in views or
// returns nil if not enough buffers are currently available.
func (s *serverTx) acquireBuffers(pktBuffer buffer.Buffer, buffers []queue.RxBuffer) (acquiredBuffers []queue.RxBuffer) {
acquiredBuffers = buffers[:0]
wantBytes := int(pktBuffer.Size())
for wantBytes > 0 {
var b []byte
if b = s.fillPipe.Pull(); b == nil {
s.fillPipe.Abort()
return nil
}
rxBuffer := queue.DecodeRxBufferHeader(b)
acquiredBuffers = append(acquiredBuffers, rxBuffer)
wantBytes -= int(rxBuffer.Size)
}
return acquiredBuffers
}
// fillPacket copies the data in the provided views into buffers pulled from the
// fillPipe and returns a slice of RxBuffers that contain the copied data as
// well as the total number of bytes copied.
//
// To avoid allocations the filledBuffers are appended to the buffers slice
// which will be grown as required. This method takes ownership of pktBuffer.
func (s *serverTx) fillPacket(pktBuffer buffer.Buffer, buffers []queue.RxBuffer) (filledBuffers []queue.RxBuffer, totalCopied uint32) {
bufs := s.acquireBuffers(pktBuffer, buffers)
if bufs == nil {
pktBuffer.Release()
return nil, 0
}
br := pktBuffer.AsBufferReader()
defer br.Close()
for i := 0; br.Len() > 0 && i < len(bufs); i++ {
buf := bufs[i]
copied, err := br.Read(s.data[buf.Offset:][:buf.Size])
buf.Size = uint32(copied)
// Copy the packet into the posted buffer.
totalCopied += bufs[i].Size
if err != nil {
return bufs, totalCopied
}
}
return bufs, totalCopied
}
func (s *serverTx) transmit(pkt *stack.PacketBuffer) bool {
buffers := make([]queue.RxBuffer, 8)
buffers, totalCopied := s.fillPacket(pkt.ToBuffer(), buffers)
if totalCopied == 0 {
// drop the packet as not enough buffers were probably available
// to send.
return false
}
b := s.completionPipe.Push(queue.RxCompletionSize(len(buffers)))
if b == nil {
return false
}
queue.EncodeRxCompletion(b, totalCopied, 0 /* reserved */)
for i := 0; i < len(buffers); i++ {
queue.EncodeRxCompletionBuffer(b, i, buffers[i])
}
s.completionPipe.Flush()
s.fillPipe.Flush()
return true
}
func (s *serverTx) notificationsEnabled() bool {
// notifications are considered to be enabled unless explicitly disabled.
return s.sharedEventFDState.Load() != queue.EventFDDisabled
}
func (s *serverTx) notify() {
if s.notificationsEnabled() {
s.eventFD.Notify()
}
}
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