init+dhcp changes for Squashfs root file systems

We can do away with a bunch of hacks now, but we’ll keep them around for a
little while to make updates easier (i.e. to boot with old and new gokr-packer
versions, just in case people don’t update both at the same time).

cmd/dhcp/dhcp.go

@@ -235,8 +235,12 @@ func main() {
 		}
 
 		if b, ok := opts[dhcp4.OptionDomainNameServer]; ok {
+			resolvConf := "/etc/resolv.conf"
+			if dest, err := os.Readlink("/etc/resolv.conf"); err == nil && dest == "/tmp/resolv.conf" {
+				resolvConf = "/tmp/resolv.conf"
+			}
 			// Get the symlink out of the way, if any.
-			if err := os.Remove("/etc/resolv.conf"); err != nil && !os.IsNotExist(err) {
+			if err := os.Remove(resolvConf); err != nil && !os.IsNotExist(err) {
 				log.Fatalf("resolv.conf: %v", err)
 			}
 			var lines []string
@@ -245,7 +249,7 @@ func main() {
 				lines = append(lines, fmt.Sprintf("search %s", string(domain)))
 			}
 			lines = append(lines, fmt.Sprintf("nameserver %v", net.IP(b)))
-			if err := ioutil.WriteFile("/etc/resolv.conf", []byte(strings.Join(lines, "\n")+"\n"), 0644); err != nil {
+			if err := ioutil.WriteFile(resolvConf, []byte(strings.Join(lines, "\n")+"\n"), 0644); err != nil {
 				log.Fatalf("resolv.conf: %v", err)
 			}
 		}

gokrazy.go

@@ -68,7 +68,7 @@ func watchdog() {
 //
 //   - mounts /dev, /tmp, /proc, /sys and /perm file systems
 //   - mounts and populate /etc tmpfs overlay
-//   - sets hostname from the /hostname file
+//   - sets hostname from the /etc/hostname file
 //   - sets HTTP password from the gokr-pw.txt file
 //   - configures the loopback network interface
 //
@@ -87,7 +87,10 @@ func Boot(userBuildTimestamp string) error {
 		return err
 	}
 
-	hostnameb, err := ioutil.ReadFile("/hostname")
+	hostnameb, err := ioutil.ReadFile("/etc/hostname")
+	if err != nil && os.IsNotExist(err) {
+		hostnameb, err = ioutil.ReadFile("/hostname")
+	}
 	if err != nil {
 		return err
 	}
@@ -98,10 +101,13 @@ func Boot(userBuildTimestamp string) error {
 
 	pw, err := ioutil.ReadFile("/perm/gokr-pw.txt")
 	if err != nil {
-		pw, err = ioutil.ReadFile("/gokr-pw.txt")
+		pw, err = ioutil.ReadFile("/etc/gokr-pw.txt")
-		if err != nil {
-			return fmt.Errorf("could read neither /perm/gokr-pw.txt nor /gokr-pw.txt: %v", err)
 	}
+	if err != nil && os.IsNotExist(err) {
+		pw, err = ioutil.ReadFile("/gokr-pw.txt")
+	}
+	if err != nil {
+		return fmt.Errorf("could read neither /perm/gokr-pw.txt, nor /etc/gokr-pw.txt, nor /gokr-pw.txt: %v", err)
 	}
 
 	httpPassword = strings.TrimSpace(string(pw))

mount.go

@@ -8,11 +8,9 @@ import (
 	"syscall"
 )
 
-func mountfs() error {
+// mountCompat deals with old FAT root file systems, to cover the case where
-	if err := syscall.Mount("tmpfs", "/tmp", "tmpfs", syscall.MS_NOSUID|syscall.MS_NODEV|syscall.MS_RELATIME, "size=50M"); err != nil {
+// users use an old gokr-packer with a new github.com/gokrazy/gokrazy package.
-		return fmt.Errorf("tmpfs on /tmp: %v", err)
+func mountCompat() error {
-	}
-
 	// Symlink /etc/resolv.conf. We cannot do this in the root file
 	// system itself, as FAT does not support symlinks.
 	if err := syscall.Mount("tmpfs", "/etc", "tmpfs", syscall.MS_NOSUID|syscall.MS_NODEV|syscall.MS_RELATIME, "size=1M"); err != nil {
@@ -40,6 +38,23 @@ func mountfs() error {
 	if err := ioutil.WriteFile("/etc/hosts", []byte("127.0.0.1 localhost\n::1 localhost\n"), 0644); err != nil {
 		return fmt.Errorf("/etc/hosts: %v", err)
 	}
+	return nil
+}
+
+func mountfs() error {
+	if err := syscall.Mount("tmpfs", "/tmp", "tmpfs", syscall.MS_NOSUID|syscall.MS_NODEV|syscall.MS_RELATIME, "size=50M"); err != nil {
+		return fmt.Errorf("tmpfs on /tmp: %v", err)
+	}
+
+	if err := os.Symlink("/proc/net/pnp", "/tmp/resolv.conf"); err != nil {
+		return fmt.Errorf("etc: %v", err)
+	}
+
+	if _, err := os.Lstat("/etc/resolv.conf"); err != nil && os.IsNotExist(err) {
+		if err := mountCompat(); err != nil {
+			return err
+		}
+	}
 
 	if err := syscall.Mount("devtmpfs", "/dev", "devtmpfs", 0, ""); err != nil {
 		if sce, ok := err.(syscall.Errno); ok && sce == syscall.EBUSY {