Noise ripped out after the bench verdict (tightly-wrapped unshielded cables move victim SNR only 0.2-0.3 dB, recorded in measurement.md dead ends): noise.go deleted with the noiser, phase clock and panel lane; configureNoise/checkPrivFlag gone so the X710 pair is untouched; console noise column, NOISE links rows and lane colors removed; driverPair rehomed to system.go, carrierUp to phy.go; history anchors to run start (frame-rate sampling and draw-clock roll kept — they fix display latency for every lane); goals/hardware/state/nics docs updated; verified on hardware (20.00G, zero errors, ECD 41m, SNR +7.6)

system.go

@@ -6,12 +6,39 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
 
+// Kernel names shift with which drivers are built in, since ethN is handed out
+// in link order rather than by slot. The driver name is the one label a port
+// keeps across kernel configs, so pairs are found by it rather than named.
+func driverPair(driver string) (string, string, error) {
+	ents, err := os.ReadDir("/sys/class/net")
+	if err != nil {
+		return "", "", err
+	}
+	var names []string
+	for _, e := range ents {
+		link, err := os.Readlink("/sys/class/net/" + e.Name() + "/device/driver")
+		if err != nil {
+			continue
+		}
+		if filepath.Base(link) == driver {
+			names = append(names, e.Name())
+		}
+	}
+	if len(names) != 2 {
+		return "", "", fmt.Errorf("want 2 %s interfaces, found %d [%s]",
+			driver, len(names), strings.Join(names, " "))
+	}
+	sort.Strings(names)
+	return names[0], names[1], nil
+}
+
 const (
 	ethtoolGRXRINGS    = 0x2d
 	ethtoolGRXCLSRLCNT = 0x2e
@@ -366,9 +393,8 @@ func getCoalesce(fd int, ifname string) (ethtoolCoalesce, error) {
 }
 
 const (
-	ethSSStats     = 1
-	ethSSPrivFlags = 2
-	ethGstringLen  = 32
+	ethSSStats    = 1
+	ethGstringLen = 32
 )
 
 // Each of these has a __u32 or __u8 tail the kernel fills past the end of the
@@ -660,67 +686,6 @@ func withIoctlSocket(fn func(fd int) []checkResult) []checkResult {
 	return fn(fd)
 }
 
-type ethtoolValue struct {
-	cmd  uint32
-	data uint32
-}
-
-// i40e leaves the module transmitting when a port is closed, so the peer never
-// sees anything happen and the copper stays trained. This flag is what makes
-// an administrative down reach the wire, and the noise cycle is switched
-// entirely through it.
-func checkPrivFlag(fd int, ifname, flag string) checkResult {
-	res := checkResult{item: ifname + " " + flag}
-	names, err := stringSetNames(fd, ifname, ethSSPrivFlags)
-	if err != nil {
-		res.err = err
-		return res
-	}
-	bit := -1
-	for i, s := range names {
-		if s == flag {
-			bit = i
-			break
-		}
-	}
-	if bit < 0 {
-		res.err = fmt.Errorf("driver has no private flag %q", flag)
-		return res
-	}
-	v := ethtoolValue{cmd: unix.ETHTOOL_GPFLAGS}
-	if err := ethtoolCall(fd, ifname, unsafe.Pointer(&v)); err != nil {
-		res.err = err
-		return res
-	}
-	if v.data&(1<<bit) != 0 {
-		res.state = "on"
-		return res
-	}
-	v.cmd = unix.ETHTOOL_SPFLAGS
-	v.data |= 1 << bit
-	if err := ethtoolCall(fd, ifname, unsafe.Pointer(&v)); err != nil {
-		res.err = err
-		res.state = "could not set"
-		return res
-	}
-	res.fixed = true
-	res.state = "was off, now on"
-	return res
-}
-
-// The noise ports get none of the test pair's tuning: nothing is measured on
-// them, so rings, coalescing and steering are all beside the point. All they
-// need is for a closed port to really drop the link.
-func configureNoise(ifnames []string) []checkResult {
-	return withIoctlSocket(func(fd int) []checkResult {
-		var out []checkResult
-		for _, ifname := range ifnames {
-			out = append(out, checkPrivFlag(fd, ifname, "link-down-on-close"))
-		}
-		return out
-	})
-}
-
 // Nothing here waits for a carrier: the two ports are the two ends of the cable
 // under test, so with no cable there is never going to be one.
 func configureSystem(ifnames []string, ethertypes []uint16) []checkResult {