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net/netmon, wgengine/userspace: purge ChangeDelta.Major and address TODOs (#17823)

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updates tailscale/corp#33891

Addresses several older the TODO's in netmon.  This removes the 
Major flag precomputes the ChangeDelta state, rather than making
consumers of ChangeDeltas sort that out themselves.   We're also seeing
a lot of ChangeDelta's being flagged as "Major" when they are
not interesting, triggering rebinds in wgengine that are not needed.  This
cleans that up and adds a host of additional tests.

The dependencies are cleaned, notably removing dependency on netmon
itself for calculating what is interesting, and what is not.  This includes letting
individual platforms set a bespoke global "IsInterestingInterface"
function.  This is only used on Darwin.

RebindRequired now roughly follows how "Major" was historically
calculated but includes some additional checks for various
uninteresting events such as changes in interface addresses that
shouldn't trigger a rebind.  This significantly reduces thrashing (by
roughly half on Darwin clients which switching between nics).   The individual
values that we roll  into RebindRequired are also exposed so that
components consuming netmap.ChangeDelta can ask more
targeted questions.

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>
This commit is contained in:
Jonathan Nobels
2025-12-17 12:32:40 -05:00
committed by GitHub
parent 0fd1670a59
commit 3e89068792
19 changed files with 754 additions and 273 deletions
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net/netmon/loghelper.go
+22 -17
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@@ -6,38 +6,43 @@ package netmon
import (
"context"
"sync"
"time"
"tailscale.com/types/logger"
"tailscale.com/util/eventbus"
)
const cooldownSeconds = 300
// LinkChangeLogLimiter returns a new [logger.Logf] that logs each unique
// format string to the underlying logger only once per major LinkChange event.
// format string to the underlying logger only once per major LinkChange event
// with a cooldownSeconds second cooldown.
//
// The logger stops tracking seen format strings when the provided context is
// done.
func LinkChangeLogLimiter(ctx context.Context, logf logger.Logf, nm *Monitor) logger.Logf {
var formatSeen sync.Map // map[string]bool
sub := eventbus.SubscribeFunc(nm.b, func(cd ChangeDelta) {
// If we're in a major change or a time jump, clear the seen map.
if cd.Major || cd.TimeJumped {
formatSeen.Clear()
var formatLastSeen sync.Map // map[string]int64
sub := eventbus.SubscribeFunc(nm.b, func(cd *ChangeDelta) {
// Any link changes that are flagged as likely require a rebind are
// interesting enough that we should log them.
if cd.RebindLikelyRequired {
formatLastSeen.Clear()
}
})
context.AfterFunc(ctx, sub.Close)
return func(format string, args ...any) {
// We only store 'true' in the map, so if it's present then it
// means we've already logged this format string.
_, loaded := formatSeen.LoadOrStore(format, true)
if loaded {
// TODO(andrew-d): we may still want to log this
// message every N minutes (1x/hour?) even if it's been
// seen, so that debugging doesn't require searching
// back in the logs for an unbounded amount of time.
//
// See: https://github.com/tailscale/tailscale/issues/13145
return
// get the current timestamp
now := time.Now().Unix()
lastSeen, ok := formatLastSeen.Load(format)
if ok {
// if we've seen this format string within the last cooldownSeconds, skip logging
if now-lastSeen.(int64) < cooldownSeconds {
return
}
}
// update the last seen timestamp for this format string
formatLastSeen.Store(format, now)
logf(format, args...)
}