Make every failed check and unreadable counter fatal instead of degrading

main.go

@@ -211,11 +211,14 @@ func lookupEndpoint(name string) (endpoint, error) {
 	}
 	var mac [6]byte
 	copy(mac[:], ifi.HardwareAddr)
-	e := endpoint{name: name, idx: ifi.Index, mac: mac, mtu: ifi.MTU}
-	if v, ok := readUint("/sys/class/net/" + name + "/speed"); ok {
-		e.speed = float64(v) / 1000
+	// The rate columns are graded against this, so a guessed speed would silently
+	// grade every reading against the wrong target.
+	v, ok := readUint("/sys/class/net/" + name + "/speed")
+	if !ok || v == 0 {
+		return endpoint{}, fmt.Errorf("%s: cannot read link speed", name)
 	}
-	return e, nil
+	return endpoint{name: name, idx: ifi.Index, mac: mac, mtu: ifi.MTU,
+		speed: float64(v) / 1000}, nil
 }
 
 func parseSizes(s string) ([]int, error) {
@@ -707,9 +710,6 @@ func run(aName, bName, sizesArg string,
 		[]bool{false, false, false, true, true}, linkRows))
 
 	target := a.speed
-	if target <= 0 {
-		target = 10
-	}
 	sizeStrs := make([]string, len(sizes))
 	for i, s := range sizes {
 		sizeStrs[i] = fmt.Sprintf("%d", s)

sock.go

@@ -25,7 +25,7 @@ func setBufForce(fd, forceOpt, opt, size int) error {
 func sockBufSize(fd, opt int) int {
 	v, err := unix.GetsockoptInt(fd, unix.SOL_SOCKET, opt)
 	if err != nil {
-		return -1
+		panic(fmt.Sprintf("reading socket buffer size: %v", err))
 	}
 	return v
 }
@@ -117,7 +117,7 @@ func newMmsghdrs(bufs [][]byte) ([]mmsghdr, []unix.Iovec) {
 func packetDrops(fd int) uint64 {
 	st, err := unix.GetsockoptTpacketStats(fd, unix.SOL_PACKET, unix.PACKET_STATISTICS)
 	if err != nil {
-		return 0
+		panic(fmt.Sprintf("reading packet drop statistics: %v", err))
 	}
 	return uint64(st.Drops)
 }

system.go

@@ -462,6 +462,7 @@ func checkGovernor(want string) checkResult {
 	paths, err := filepath.Glob("/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor")
 	if err != nil || len(paths) == 0 {
 		res.err = fmt.Errorf("no cpufreq governors found")
+		res.fatal = true
 		return res
 	}
 	var wrong []string
@@ -470,6 +471,7 @@ func checkGovernor(want string) checkResult {
 		b, err := os.ReadFile(p)
 		if err != nil {
 			res.err = err
+			res.fatal = true
 			return res
 		}
 		got := strings.TrimSpace(string(b))
@@ -490,6 +492,7 @@ func checkGovernor(want string) checkResult {
 		if err := os.WriteFile(p, []byte(want), 0o644); err != nil {
 			res.err = err
 			res.state = fmt.Sprintf("could not set %s", p)
+			res.fatal = true
 			return res
 		}
 	}
@@ -532,6 +535,7 @@ func checkCoalesce(fd int, ifname string, rxUsecs, txUsecs uint32) checkResult {
 	ec, err := getCoalesce(fd, ifname)
 	if err != nil {
 		res.err = err
+		res.fatal = true
 		return res
 	}
 	desc := func(e ethtoolCoalesce) string {
@@ -552,6 +556,7 @@ func checkCoalesce(fd int, ifname string, rxUsecs, txUsecs uint32) checkResult {
 	if err := ethtoolCall(fd, ifname, unsafe.Pointer(&ec)); err != nil {
 		res.err = err
 		res.state = "could not set"
+		res.fatal = true
 		return res
 	}
 	res.fixed = true
@@ -564,6 +569,7 @@ func checkRings(fd int, ifname string, rxWant, txWant uint32) checkResult {
 	rp, err := getRings(fd, ifname)
 	if err != nil {
 		res.err = err
+		res.fatal = true
 		return res
 	}
 	rx := min(rxWant, rp.rxMaxPending)
@@ -579,6 +585,7 @@ func checkRings(fd int, ifname string, rxWant, txWant uint32) checkResult {
 	if err := ethtoolCall(fd, ifname, unsafe.Pointer(&rp)); err != nil {
 		res.err = err
 		res.state = "could not set"
+		res.fatal = true
 		return res
 	}
 	res.fixed = true