Detect mounts by mount root, wait for the touchscreen, and default to eth0/eth1

init.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"time"
 
 	"golang.org/x/sys/unix"
 )
@@ -21,11 +22,26 @@ type mountSpec struct {
 var wantMounts = []mountSpec{
 	{"/proc", "proc", unix.PROC_SUPER_MAGIC, unix.MS_NOSUID | unix.MS_NODEV | unix.MS_NOEXEC},
 	{"/sys", "sysfs", unix.SYSFS_MAGIC, unix.MS_NOSUID | unix.MS_NODEV | unix.MS_NOEXEC},
-	// devtmpfs reports itself as tmpfs, so an existing tmpfs on /dev is taken
-	// as good enough; the kernel populates the nodes either way.
+	// devtmpfs reports itself as tmpfs, which is why the magic alone is not
+	// enough to tell it apart from the directory it would be mounted over.
 	{"/dev", "devtmpfs", unix.TMPFS_MAGIC, unix.MS_NOSUID},
 }
 
+// Whether something is mounted here, as opposed to this being a plain
+// directory on whatever filesystem contains it. The type alone cannot answer
+// that: booted from an initramfs the root is itself tmpfs, so an empty /dev
+// directory on it is indistinguishable by magic from a mounted devtmpfs.
+func isMountRoot(dir string) (bool, error) {
+	var stx unix.Statx_t
+	if err := unix.Statx(unix.AT_FDCWD, dir, 0, unix.STATX_BASIC_STATS, &stx); err != nil {
+		return false, err
+	}
+	if stx.Attributes_mask&unix.STATX_ATTR_MOUNT_ROOT == 0 {
+		return false, fmt.Errorf("kernel does not report STATX_ATTR_MOUNT_ROOT")
+	}
+	return stx.Attributes&unix.STATX_ATTR_MOUNT_ROOT != 0, nil
+}
+
 func checkMount(m mountSpec) checkResult {
 	res := checkResult{item: "mount " + m.dir}
 	var st unix.Statfs_t
@@ -43,7 +59,13 @@ func checkMount(m mountSpec) checkResult {
 		res.fatal = true
 		return res
 	}
-	if int64(st.Type) == m.magic {
+	mounted, err := isMountRoot(m.dir)
+	if err != nil {
+		res.err = err
+		res.fatal = true
+		return res
+	}
+	if mounted && int64(st.Type) == m.magic {
 		res.state = m.fstype + " already mounted"
 		return res
 	}
@@ -69,3 +91,45 @@ func mountFilesystems() []checkResult {
 	}
 	return out
 }
+
+const (
+	touchTimeout = 30 * time.Second
+	touchPoll    = 100 * time.Millisecond
+)
+
+// USB enumerates asynchronously and the kernel hands us control long before the
+// bus has settled, so unlike everything else here the touchscreen is genuinely
+// not there yet rather than absent. It is the only device we wait for.
+func waitForTouchscreen() checkResult {
+	res := checkResult{item: "touchscreen"}
+	start := time.Now()
+	for {
+		f, err := findTouchscreen()
+		if err == nil {
+			f.Close()
+			waited := time.Since(start)
+			if waited < touchPoll {
+				res.state = "ready"
+				return res
+			}
+			res.fixed = true
+			res.state = fmt.Sprintf("ready after %.1fs", waited.Seconds())
+			return res
+		}
+		if time.Since(start) >= touchTimeout {
+			res.err = fmt.Errorf("%w after %s", err, touchTimeout)
+			res.fatal = true
+			return res
+		}
+		time.Sleep(touchPoll)
+	}
+}
+
+func bootstrap() []checkResult {
+	out := mountFilesystems()
+	// /dev/input/event* only exists once devtmpfs is mounted above.
+	if out[len(out)-1].fatal {
+		return out
+	}
+	return append(out, waitForTouchscreen())
+}

main.go

@@ -627,8 +627,10 @@ type config struct {
 
 func main() {
 	var (
-		aName    = flag.String("a", "", "first interface")
-		bName    = flag.String("b", "", "second interface")
+		// The names the kernel gives the only two ports built into it, since as
+		// PID 1 there is no udev to rename them and no command line to pass.
+		aName    = flag.String("a", "eth0", "first interface")
+		bName    = flag.String("b", "eth1", "second interface")
 		sizesArg = flag.String("sizes", "64,128,256,512,1024,1280,1514", "frame sizes in bytes, excluding FCS, cycled per packet")
 		streams  = flag.Int("streams", 7, "independent streams per direction, capped by rx rings; each gets its own ethertype, steered by a flow rule to its own rx queue")
 		batch    = flag.Int("batch", 64, "frames per sendmmsg/recvmmsg call")
@@ -659,15 +661,12 @@ const (
 func run(aName, bName, sizesArg string,
 	nStreams, batch int, nsPerM float64) error {
 
-	if aName == "" || bName == "" {
-		return fmt.Errorf("both -a and -b are required")
-	}
 	sizes, err := parseSizes(sizesArg)
 	if err != nil {
 		return err
 	}
 
-	if err := reportChecks("MOUNTS", mountFilesystems()); err != nil {
+	if err := reportChecks("BOOT", bootstrap()); err != nil {
 		return err
 	}