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net/sockopts,wgengine/magicsock: export socket buffer sizing logic (#16909)

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For eventual use by net/udprelay.Server

Updates tailscale/corp#31164

Signed-off-by: Jordan Whited <jordan@tailscale.com>
This commit is contained in:
Jordan Whited
2025-08-20 16:24:00 -07:00
committed by GitHub
parent b48d2de6ab
commit 641a90ea33
11 changed files with 119 additions and 52 deletions
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26
wgengine/magicsock/magicsock.go
View File

@@ -45,6 +45,7 @@ import (
"tailscale.com/net/packet"
"tailscale.com/net/ping"
"tailscale.com/net/portmapper"
"tailscale.com/net/sockopts"
"tailscale.com/net/sockstats"
"tailscale.com/net/stun"
"tailscale.com/net/tstun"
@@ -3857,20 +3858,19 @@ func (c *Conn) DebugForcePreferDERP(n int) {
c.netChecker.SetForcePreferredDERP(n)
}
// portableTrySetSocketBuffer sets SO_SNDBUF and SO_RECVBUF on pconn to socketBufferSize,
// logging an error if it occurs.
func portableTrySetSocketBuffer(pconn nettype.PacketConn, logf logger.Logf) {
if runtime.GOOS == "plan9" {
// Not supported. Don't try. Avoid logspam.
return
}
if c, ok := pconn.(*net.UDPConn); ok {
// Attempt to increase the buffer size, and allow failures.
if err := c.SetReadBuffer(socketBufferSize); err != nil {
logf("magicsock: failed to set UDP read buffer size to %d: %v", socketBufferSize, err)
// trySetSocketBuffer attempts to set SO_SNDBUFFORCE and SO_RECVBUFFORCE which
// can overcome the limit of net.core.{r,w}mem_max, but require CAP_NET_ADMIN.
// It falls back to the portable implementation if that fails, which may be
// silently capped to net.core.{r,w}mem_max.
func trySetSocketBuffer(pconn nettype.PacketConn, logf logger.Logf) {
directions := []sockopts.BufferDirection{sockopts.ReadDirection, sockopts.WriteDirection}
for _, direction := range directions {
forceErr, portableErr := sockopts.SetBufferSize(pconn, direction, socketBufferSize)
if forceErr != nil {
logf("magicsock: [warning] failed to force-set UDP %v buffer size to %d: %v; using kernel default values (impacts throughput only)", direction, socketBufferSize, forceErr)
}
if err := c.SetWriteBuffer(socketBufferSize); err != nil {
logf("magicsock: failed to set UDP write buffer size to %d: %v", socketBufferSize, err)
if portableErr != nil {
logf("magicsock: failed to set UDP %v buffer size to %d: %v", direction, socketBufferSize, portableErr)
}
}
}

7
wgengine/magicsock/magicsock_default.go
View File

@@ -9,15 +9,8 @@ import (
"errors"
"fmt"
"io"
"tailscale.com/types/logger"
"tailscale.com/types/nettype"
)
func (c *Conn) listenRawDisco(family string) (io.Closer, error) {
return nil, fmt.Errorf("raw disco listening not supported on this OS: %w", errors.ErrUnsupported)
}
func trySetSocketBuffer(pconn nettype.PacketConn, logf logger.Logf) {
portableTrySetSocketBuffer(pconn, logf)
}

29
wgengine/magicsock/magicsock_linux.go
View File

@@ -13,7 +13,6 @@ import (
"net"
"net/netip"
"strings"
"syscall"
"time"
"github.com/mdlayher/socket"
@@ -28,7 +27,6 @@ import (
"tailscale.com/types/ipproto"
"tailscale.com/types/key"
"tailscale.com/types/logger"
"tailscale.com/types/nettype"
)
const (
@@ -489,30 +487,3 @@ func printSockaddr(sa unix.Sockaddr) string {
return fmt.Sprintf("unknown(%T)", sa)
}
}
// trySetSocketBuffer attempts to set SO_SNDBUFFORCE and SO_RECVBUFFORCE which
// can overcome the limit of net.core.{r,w}mem_max, but require CAP_NET_ADMIN.
// It falls back to the portable implementation if that fails, which may be
// silently capped to net.core.{r,w}mem_max.
func trySetSocketBuffer(pconn nettype.PacketConn, logf logger.Logf) {
if c, ok := pconn.(*net.UDPConn); ok {
var errRcv, errSnd error
rc, err := c.SyscallConn()
if err == nil {
rc.Control(func(fd uintptr) {
errRcv = syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_RCVBUFFORCE, socketBufferSize)
if errRcv != nil {
logf("magicsock: [warning] failed to force-set UDP read buffer size to %d: %v; using kernel default values (impacts throughput only)", socketBufferSize, errRcv)
}
errSnd = syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_SNDBUFFORCE, socketBufferSize)
if errSnd != nil {
logf("magicsock: [warning] failed to force-set UDP write buffer size to %d: %v; using kernel default values (impacts throughput only)", socketBufferSize, errSnd)
}
})
}
if err != nil || errRcv != nil || errSnd != nil {
portableTrySetSocketBuffer(pconn, logf)
}
}
}

60
wgengine/magicsock/magicsock_unix_test.go
View File

@@ -1,60 +0,0 @@
// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
//go:build unix
package magicsock
import (
"net"
"syscall"
"testing"
"tailscale.com/types/nettype"
)
func TestTrySetSocketBuffer(t *testing.T) {
c, err := net.ListenPacket("udp", ":0")
if err != nil {
t.Fatal(err)
}
defer c.Close()
rc, err := c.(*net.UDPConn).SyscallConn()
if err != nil {
t.Fatal(err)
}
getBufs := func() (int, int) {
var rcv, snd int
rc.Control(func(fd uintptr) {
rcv, err = syscall.GetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
if err != nil {
t.Errorf("getsockopt(SO_RCVBUF): %v", err)
}
snd, err = syscall.GetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_SNDBUF)
if err != nil {
t.Errorf("getsockopt(SO_SNDBUF): %v", err)
}
})
return rcv, snd
}
curRcv, curSnd := getBufs()
trySetSocketBuffer(c.(nettype.PacketConn), t.Logf)
newRcv, newSnd := getBufs()
if curRcv > newRcv {
t.Errorf("SO_RCVBUF decreased: %v -> %v", curRcv, newRcv)
}
if curSnd > newSnd {
t.Errorf("SO_SNDBUF decreased: %v -> %v", curSnd, newSnd)
}
// On many systems we may not increase the value, particularly running as a
// regular user, so log the information for manual verification.
t.Logf("SO_RCVBUF: %v -> %v", curRcv, newRcv)
t.Logf("SO_SNDBUF: %v -> %v", curRcv, newRcv)
}