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>

internal/image/cpio.go

@@ -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)
+}

internal/image/service.go

@@ -53,8 +53,24 @@ func (s *Service) Upload(ctx context.Context, p UploadParams) (*model.Image, err
 		return nil, fmt.Errorf("extract ISO: %w", err)
 	}
 
+	report := func(stage, detail string) {
+		if p.OnProgress != nil {
+			p.OnProgress(stage, detail)
+		}
+	}
+	report("packaging", "Creating PXE boot image (embedding ISO in initrd)...")
+
+	origInitrdPath := filepath.Join(destDir, result.InitrdFilename)
+	origISOPath := filepath.Join(destDir, result.ISOFilename)
+	pxeInitrdFile := "initrd-pxe.img"
+	pxeInitrdPath := filepath.Join(destDir, pxeInitrdFile)
+	if err := CreatePXEInitrd(origInitrdPath, origISOPath, pxeInitrdPath); err != nil {
+		os.RemoveAll(destDir)
+		return nil, fmt.Errorf("create PXE initrd: %w", err)
+	}
+
 	kernelPath := filepath.Join(p.Name, result.KernelFilename)
-	initrdPath := filepath.Join(p.Name, result.InitrdFilename)
+	initrdPath := filepath.Join(p.Name, pxeInitrdFile)
 	isoPath := filepath.Join(p.Name, result.ISOFilename)
 
 	id, err := s.Store.Create(ctx, model.Image{

internal/pxe/ipxe.go

@@ -7,11 +7,16 @@ import (
 )
 
 func BuildIPXEScript(publicURL string, img *model.Image, mac string) string {
-	isoURL := fmt.Sprintf("%s/images/boot/%s", publicURL, img.ISOPath)
+	kernelURL := fmt.Sprintf("%s/images/boot/%s", publicURL, img.KernelPath)
+	initrdURL := fmt.Sprintf("%s/images/boot/%s", publicURL, img.InitrdPath)
 
 	return fmt.Sprintf(`#!ipxe
 echo Provisioning: booting %s on ${mac}
-echo Booting ISO via HTTP SAN...
+echo Loading kernel...
-sanboot %s
+kernel %s ramdisk_size=16777216 vga=791 video=vesafb:lfb:on rw quiet splash=verbose rdinit=/pxe-init initrd=initrd
-`, img.Name, isoURL)
+echo Loading initrd (this may take a few minutes)...
+initrd --name initrd %s
+echo Booting...
+boot
+`, img.Name, kernelURL, initrdURL)
 }