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net/interfaces: cache "home" router lookup on big Linux routers

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This is a continuation of the earlier 2a67beaacf but more aggressive;
this now remembers that we failed to find the "home" router IP so we
don't try again later on the next call.

Updates #7621

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2023-04-17 09:40:37 -07:00 committed by Brad Fitzpatrick
parent c5150eae67
commit 162488a775
1 changed files with 16 additions and 1 deletions
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17
net/interfaces/interfaces_linux.go
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@ -98,7 +98,22 @@ func likelyHomeRouterIPLinux() (ret netip.Addr, ok bool) {
} }
log.Printf("interfaces: failed to read /proc/net/route: %v", err) log.Printf("interfaces: failed to read /proc/net/route: %v", err)
} }
return ret, ret.IsValid() if ret.IsValid() {
return ret, true
}
if lineNum >= maxProcNetRouteRead {
// If we went over our line limit without finding an answer, assume
// we're a big fancy Linux router (or at least not a home system)
// and set the error bit so we stop trying this in the future (and wasting CPU).
// See https://github.com/tailscale/tailscale/issues/7621.
//
// Remember that "likelyHomeRouterIP" exists purely to find the port
// mapping service (UPnP, PMP, PCP) often present on a home router. If we hit
// the route (line) limit without finding an answer, we're unlikely to ever
// find one in the future.
procNetRouteErr.Store(true)
}
return netip.Addr{}, false
} }
// Android apps don't have permission to read /proc/net/route, at // Android apps don't have permission to read /proc/net/route, at