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65dc711c76
Add a nodeAttr to enable/disable peer path MTU discovery. Updates #311 Signed-off-by: Val <valerie@tailscale.com>
108 lines
3.7 KiB
Go
108 lines
3.7 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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//go:build (darwin && !ios) || (linux && !android)
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package magicsock
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// Peer path MTU routines shared by platforms that implement it.
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// DontFragSetting returns true if at least one of the underlying sockets of
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// this connection is a UDP socket with the don't fragment bit set, otherwise it
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// returns false. It also returns an error if either connection returned an error
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// other than errUnsupportedConnType.
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func (c *Conn) DontFragSetting() (bool, error) {
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df4, err4 := c.getDontFragment("udp4")
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df6, err6 := c.getDontFragment("udp6")
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df := df4 || df6
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err := err4
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if err4 != nil && err4 != errUnsupportedConnType {
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err = err6
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}
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if err == errUnsupportedConnType {
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err = nil
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}
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return df, err
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}
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// ShouldPMTUD returns true if this client should try to enable peer MTU
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// discovery, false otherwise.
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func (c *Conn) ShouldPMTUD() bool {
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if v, ok := debugEnablePMTUD().Get(); ok {
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if debugPMTUD() {
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c.logf("magicsock: peermtu: peer path MTU discovery set via envknob to %v", v)
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}
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return v
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}
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if c.controlKnobs != nil {
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if v := c.controlKnobs.PeerMTUEnable.Load(); v {
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if debugPMTUD() {
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c.logf("magicsock: peermtu: peer path MTU discovery enabled by control")
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}
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return v
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}
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}
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if debugPMTUD() {
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c.logf("magicsock: peermtu: peer path MTU discovery set by default to false")
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}
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return false // Until we feel confident PMTUD is solid.
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}
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// PeerMTUEnabled returns true if this Conn is has peer path MTU discovery enabled.
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func (c *Conn) PeerMTUEnabled() bool {
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return c.peerMTUEnabled.Load()
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}
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// UpdatePMTUD configures underlying sockets of this Conn to enable or disable
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// peer path MTU discovery according to the current configuration.
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//
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// Enabling or disabling peer path MTU discovery requires setting the don't
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// fragment bit on its two underlying pconns. There are three distinct results
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// for this operation on each pconn:
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//
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// 1. Success
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// 2. Failure (not supported on this platform, or supported but failed)
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// 3. Not a UDP socket (most likely one of IPv4 or IPv6 couldn't be used)
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//
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// To simplify the fast path for the most common case, we set the PMTUD status
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// of the overall Conn according to the results of setting the sockopt on pconn
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// as follows:
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//
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// 1. Both setsockopts succeed: PMTUD status update succeeds
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// 2. One succeeds, one returns not a UDP socket: PMTUD status update succeeds
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// 4. Neither setsockopt succeeds: PMTUD disabled
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// 3. Either setsockopt fails: PMTUD disabled
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//
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// If the PMTUD settings changed, it resets the endpoint state so that it will
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// re-probe path MTUs to this peer.
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func (c *Conn) UpdatePMTUD() {
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if debugPMTUD() {
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df4, err4 := c.getDontFragment("udp4")
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df6, err6 := c.getDontFragment("udp6")
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c.logf("magicsock: peermtu: peer MTU status %v DF bit status: v4: %v (%v) v6: %v (%v)", c.peerMTUEnabled.Load(), df4, err4, df6, err6)
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}
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enable := c.ShouldPMTUD()
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if c.peerMTUEnabled.Load() == enable {
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c.logf("magicsock: peermtu: peer MTU status is %v", enable)
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return
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}
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newStatus := enable
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err4 := c.setDontFragment("udp4", enable)
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err6 := c.setDontFragment("udp6", enable)
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anySuccess := err4 == nil || err6 == nil
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noFailures := (err4 == nil || err4 == errUnsupportedConnType) && (err6 == nil || err6 == errUnsupportedConnType)
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if anySuccess && noFailures {
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c.logf("magicsock: peermtu: peer MTU status updated to %v", newStatus)
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} else {
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c.logf("[unexpected] magicsock: peermtu: updating peer MTU status to %v failed (v4: %v, v6: %v), disabling", enable, err4, err6)
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_ = c.setDontFragment("udp4", false)
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_ = c.setDontFragment("udp6", false)
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newStatus = false
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}
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c.peerMTUEnabled.Store(newStatus)
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c.resetEndpointStates()
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}
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