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/* SPDX-License-Identifier: MIT
*
* Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
*/
package wintun
import (
"runtime"
"unsafe"
"golang.org/x/sys/windows"
)
const (
PacketAlignment = 4 // Number of bytes packets are aligned to in rings
PacketSizeMax = 0xffff // Maximum packet size
PacketCapacity = 0x800000 // Ring capacity, 8MiB
PacketTrailingSize = uint32(unsafe.Sizeof(PacketHeader{})) + ((PacketSizeMax + (PacketAlignment - 1)) &^ (PacketAlignment - 1)) - PacketAlignment
ioctlRegisterRings = (51820 << 16) | (0x970 << 2) | 0 /*METHOD_BUFFERED*/ | (0x3 /*FILE_READ_DATA | FILE_WRITE_DATA*/ << 14)
)
type PacketHeader struct {
Size uint32
}
type Packet struct {
PacketHeader
Data [PacketSizeMax]byte
}
type Ring struct {
Head uint32
Tail uint32
Alertable int32
Data [PacketCapacity + PacketTrailingSize]byte
}
type RingDescriptor struct {
Send, Receive struct {
Size uint32
Ring *Ring
TailMoved windows.Handle
}
}
// Wrap returns value modulo ring capacity
func (rb *Ring) Wrap(value uint32) uint32 {
return value & (PacketCapacity - 1)
}
// Aligns a packet size to PacketAlignment
func PacketAlign(size uint32) uint32 {
return (size + (PacketAlignment - 1)) &^ (PacketAlignment - 1)
}
func NewRingDescriptor() (descriptor *RingDescriptor, err error) {
descriptor = new(RingDescriptor)
allocatedRegion, err := windows.VirtualAlloc(0, unsafe.Sizeof(Ring{})*2, windows.MEM_COMMIT|windows.MEM_RESERVE, windows.PAGE_READWRITE)
if err != nil {
return
}
defer func() {
if err != nil {
descriptor.free()
descriptor = nil
}
}()
descriptor.Send.Size = uint32(unsafe.Sizeof(Ring{}))
descriptor.Send.Ring = (*Ring)(unsafe.Pointer(allocatedRegion))
descriptor.Send.TailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
if err != nil {
return
}
descriptor.Receive.Size = uint32(unsafe.Sizeof(Ring{}))
descriptor.Receive.Ring = (*Ring)(unsafe.Pointer(allocatedRegion + unsafe.Sizeof(Ring{})))
descriptor.Receive.TailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
if err != nil {
windows.CloseHandle(descriptor.Send.TailMoved)
return
}
runtime.SetFinalizer(descriptor, func(d *RingDescriptor) { d.free() })
return
}
func (descriptor *RingDescriptor) free() {
if descriptor.Send.Ring != nil {
windows.VirtualFree(uintptr(unsafe.Pointer(descriptor.Send.Ring)), 0, windows.MEM_RELEASE)
descriptor.Send.Ring = nil
descriptor.Receive.Ring = nil
}
}
func (descriptor *RingDescriptor) Close() {
if descriptor.Send.TailMoved != 0 {
windows.CloseHandle(descriptor.Send.TailMoved)
descriptor.Send.TailMoved = 0
}
if descriptor.Send.TailMoved != 0 {
windows.CloseHandle(descriptor.Receive.TailMoved)
descriptor.Receive.TailMoved = 0
}
}
func (wintun *Interface) Register(descriptor *RingDescriptor) (windows.Handle, error) {
handle, err := wintun.handle()
if err != nil {
return 0, err
}
var bytesReturned uint32
err = windows.DeviceIoControl(handle, ioctlRegisterRings, (*byte)(unsafe.Pointer(descriptor)), uint32(unsafe.Sizeof(*descriptor)), nil, 0, &bytesReturned, nil)
if err != nil {
return 0, err
}
return handle, nil
}
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