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envknob,net/tstun,wgengine: use TS_DEBUG_MTU consistently

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Noted on #5915 TS_DEBUG_MTU was not used consistently everywhere.
Extract the default into a function that can apply this centrally and
use it everywhere.

Added envknob.Lookup{Int,Uint}Sized to make it easier to keep CodeQL
happy when using converted values.

Updates #5915

Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
James Tucker
2023-03-30 10:37:06 -07:00
committed by James Tucker
parent 8ed4fd1dbc
commit 40fa2a420c
7 changed files with 105 additions and 25 deletions
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5
wgengine/netstack/netstack.go
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@ -146,7 +146,6 @@ type Impl struct {
}
const nicID = 1
const mtu = tstun.DefaultMTU
// maxUDPPacketSize is the maximum size of a UDP packet we copy in startPacketCopy
// when relaying UDP packets. We don't use the 'mtu' const in anticipation of
@ -179,7 +178,7 @@ func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magi
if tcpipErr != nil {
return nil, fmt.Errorf("could not enable TCP SACK: %v", tcpipErr)
}
linkEP := channel.New(512, mtu, "")
linkEP := channel.New(512, tstun.DefaultMTU(), "")
if tcpipProblem := ipstack.CreateNIC(nicID, linkEP); tcpipProblem != nil {
return nil, fmt.Errorf("could not create netstack NIC: %v", tcpipProblem)
}
@ -1078,7 +1077,7 @@ func (ns *Impl) acceptUDP(r *udp.ForwarderRequest) {
func (ns *Impl) handleMagicDNSUDP(srcAddr netip.AddrPort, c *gonet.UDPConn) {
// In practice, implementations are advised not to exceed 512 bytes
// due to fragmenting. Just to be sure, we bump all the way to the MTU.
const maxUDPReqSize = mtu
var maxUDPReqSize = tstun.DefaultMTU()
// Packets are being generated by the local host, so there should be
// very, very little latency. 150ms was chosen as something of an upper
// bound on resource usage, while hopefully still being long enough for