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//go:build linux
/* SPDX-License-Identifier: MIT
*
* Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
*/
package conn
import (
"fmt"
"unsafe"
"golang.org/x/sys/unix"
)
const (
sizeOfGSOData = 2
)
// getGSOSize parses control for UDP_GRO and if found returns its GSO size data.
func getGSOSize(control []byte) (int, error) {
var (
hdr unix.Cmsghdr
data []byte
rem = control
err error
)
for len(rem) > unix.SizeofCmsghdr {
hdr, data, rem, err = unix.ParseOneSocketControlMessage(rem)
if err != nil {
return 0, fmt.Errorf("error parsing socket control message: %w", err)
}
if hdr.Level == unix.SOL_UDP && hdr.Type == unix.UDP_GRO && len(data) >= sizeOfGSOData {
var gso uint16
copy(unsafe.Slice((*byte)(unsafe.Pointer(&gso)), sizeOfGSOData), data[:sizeOfGSOData])
return int(gso), nil
}
}
return 0, nil
}
// setGSOSize sets a UDP_SEGMENT in control based on gsoSize. It leaves existing
// data in control untouched.
func setGSOSize(control *[]byte, gsoSize uint16) {
existingLen := len(*control)
avail := cap(*control) - existingLen
space := unix.CmsgSpace(sizeOfGSOData)
if avail < space {
return
}
*control = (*control)[:cap(*control)]
gsoControl := (*control)[existingLen:]
hdr := (*unix.Cmsghdr)(unsafe.Pointer(&(gsoControl)[0]))
hdr.Level = unix.SOL_UDP
hdr.Type = unix.UDP_SEGMENT
hdr.SetLen(unix.CmsgLen(sizeOfGSOData))
copy((gsoControl)[unix.SizeofCmsghdr:], unsafe.Slice((*byte)(unsafe.Pointer(&gsoSize)), sizeOfGSOData))
*control = (*control)[:existingLen+space]
}
// gsoControlSize returns the recommended buffer size for pooling UDP
// offloading control data.
var gsoControlSize = unix.CmsgSpace(sizeOfGSOData)
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