remove dep on udev

- remove the need to map host's /dev
- remove race issues or need to have a working `udevadm settle`

cmd/dkl-local-server/udev.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// Simulate a udev run for our needs
+func syncSysToDev() {
+	// loop devices
+	sysPaths, _ := filepath.Glob("/sys/devices/virtual/block/loop*/**/dev")
+	for _, sysPath := range sysPaths {
+		mknodBlk(sysPath)
+	}
+}
+
+func mknodBlk(sysPath string) {
+	devPath := "/dev/" + filepath.Base(filepath.Dir(sysPath))
+	if _, err := os.Stat(devPath); os.IsNotExist(err) {
+		// ok
+	} else if err != nil {
+		log.Printf("stat %s failed: %v", devPath, err)
+		return
+	} else {
+		return // exists
+	}
+
+	devBytes, err := os.ReadFile(sysPath)
+	if err != nil {
+		log.Printf("read %s failed: %v", sysPath, err)
+		return
+	}
+	devBytes = bytes.TrimSpace(devBytes)
+
+	// rust: let Some(dev) = devBytes.split_once(':').filter_map(|a,b| Some(mkdev(a.parse().ok()?, b.parse().ok()?)));
+	majorStr, minorStr, ok := strings.Cut(string(devBytes), ":")
+	if !ok {
+		log.Printf("%s: invalid dev string: %s", sysPath, string(devBytes))
+		return
+	}
+	major, err := strconv.ParseUint(majorStr, 10, 32)
+	if err != nil {
+		log.Printf("%s: invalid major: %q", sysPath, majorStr)
+		return
+	}
+	minor, err := strconv.ParseUint(minorStr, 10, 32)
+	if err != nil {
+		log.Printf("%s: invalid minor: %q", sysPath, minorStr)
+		return
+	}
+
+	devMajMin := int(unix.Mkdev(uint32(major), uint32(minor)))
+
+	log.Printf("mknod %s b %d %d", devPath, major, minor)
+	unix.Mknod(devPath, syscall.S_IFBLK|0o0600, devMajMin)
+}