Embed ISO in initrd for PXE boot with loop-mount wrapper

Instead of sanboot (which can't pass kernel params for automation), switch back to kernel/initrd boot. The ISO is embedded in the initrd as a CPIO append. A pxe-init wrapper script loop-mounts the ISO before handing off to the original init, so the installer finds it as a block device. Uses rdinit=/pxe-init kernel parameter. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-05-14 12:11:18 -04:00
parent a8f8801a90
commit e2dd78d8f9
3 changed files with 147 additions and 5 deletions
@@ -0,0 +1,121 @@
+package image
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+const pxeInitScript = `#!/bin/sh
+mkdir -p /dev
+mount -t devtmpfs devtmpfs /dev 2>/dev/null
+losetup /dev/loop0 /proxmox.iso 2>/dev/null
+umount /dev 2>/dev/null
+exec /init "$@"
+`
+
+func CreatePXEInitrd(origInitrdPath, isoPath, outputPath string) error {
+	out, err := os.Create(outputPath)
+	if err != nil {
+		return fmt.Errorf("create output: %w", err)
+	}
+	defer out.Close()
+
+	orig, err := os.Open(origInitrdPath)
+	if err != nil {
+		return fmt.Errorf("open initrd: %w", err)
+	}
+	if _, err := io.Copy(out, orig); err != nil {
+		orig.Close()
+		return fmt.Errorf("copy initrd: %w", err)
+	}
+	orig.Close()
+
+	if err := writeCPIOEntry(out, "pxe-init", []byte(pxeInitScript), 0o100755, 1); err != nil {
+		return err
+	}
+
+	isoStat, err := os.Stat(isoPath)
+	if err != nil {
+		return fmt.Errorf("stat iso: %w", err)
+	}
+	isoFile, err := os.Open(isoPath)
+	if err != nil {
+		return fmt.Errorf("open iso: %w", err)
+	}
+	defer isoFile.Close()
+	if err := writeCPIOEntryFromReader(out, "proxmox.iso", isoFile, isoStat.Size(), 0o100644, 2); err != nil {
+		return err
+	}
+
+	return writeCPIOTrailer(out)
+}
+
+func writeCPIOEntry(w io.Writer, name string, data []byte, mode uint32, ino uint32) error {
+	if err := writeCPIOHeader(w, name, int64(len(data)), mode, ino); err != nil {
+		return err
+	}
+	if _, err := w.Write(data); err != nil {
+		return err
+	}
+	if pad := (4 - len(data)%4) % 4; pad > 0 {
+		if _, err := w.Write(make([]byte, pad)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func writeCPIOEntryFromReader(w io.Writer, name string, r io.Reader, size int64, mode uint32, ino uint32) error {
+	if err := writeCPIOHeader(w, name, size, mode, ino); err != nil {
+		return err
+	}
+	if _, err := io.Copy(w, r); err != nil {
+		return err
+	}
+	if pad := (4 - int(size%4)) % 4; pad > 0 {
+		if _, err := w.Write(make([]byte, pad)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func writeCPIOHeader(w io.Writer, name string, fileSize int64, mode uint32, ino uint32) error {
+	nameLen := len(name) + 1
+	hdr := fmt.Sprintf("070701%08X%08X%08X%08X%08X%08X%08X%08X%08X%08X%08X%08X%08X",
+		ino,      // ino
+		mode,     // mode
+		0,        // uid
+		0,        // gid
+		1,        // nlink
+		0,        // mtime
+		fileSize, // filesize
+		0,        // devmajor
+		0,        // devminor
+		0,        // rdevmajor
+		0,        // rdevminor
+		nameLen,  // namesize
+		0,        // check
+	)
+	if _, err := io.WriteString(w, hdr); err != nil {
+		return err
+	}
+	if _, err := io.WriteString(w, name); err != nil {
+		return err
+	}
+	if _, err := w.Write([]byte{0}); err != nil {
+		return err
+	}
+	totalHeader := 110 + nameLen
+	if pad := (4 - totalHeader%4) % 4; pad > 0 {
+		if _, err := w.Write(make([]byte, pad)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func writeCPIOTrailer(w io.Writer) error {
+	return writeCPIOHeader(w, "TRAILER!!!", 0, 0, 0)
+}