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Switch from sanboot to kernel/initrd boot with PXE overlay for ISO download
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sanboot makes the ISO visible to UEFI but invisible to the Linux kernel
after ExitBootServices(). Switch to direct kernel/initrd boot with a small
CPIO overlay containing /pxe-init — a shell script that loads NIC drivers,
configures DHCP, downloads the ISO via wget, and creates a loop device
before handing off to the Proxmox installer init.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Josh Wright
2026-05-14 18:57:43 -04:00
parent 1bb6a44fc6
commit b1eab33b78
3 changed files with 68 additions and 53 deletions
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internal/image/cpio.go
+42 -44
View File
@@ -7,47 +7,60 @@ import (
)
const pxeInitScript = `#!/bin/sh
mkdir -p /dev
mount -t devtmpfs devtmpfs /dev 2>/dev/null
losetup /dev/loop0 /proxmox.iso 2>/dev/null
mount -t proc proc /proc 2>/dev/null
mount -t sysfs sys /sys 2>/dev/null
mount -t devtmpfs dev /dev 2>/dev/null
mkdir -p /tmp
ISO_URL=""
for param in $(cat /proc/cmdline); do
case $param in
prov.iso=*) ISO_URL="${param#prov.iso=}" ;;
esac
done
if [ -n "$ISO_URL" ]; then
echo "=== PXE: Setting up network ==="
for mod in e1000 e1000e igb ixgbe i40e ice tg3 bnxt_en r8169 virtio_net; do
modprobe $mod 2>/dev/null
done
sleep 2
for iface in $(ls /sys/class/net/ 2>/dev/null | grep -v lo); do
ip link set "$iface" up 2>/dev/null
if udhcpc -i "$iface" -n -q -t 5 2>/dev/null; then
echo "PXE: Network up on $iface"
break
fi
done
echo "=== PXE: Downloading ISO ==="
wget -O /tmp/proxmox.iso "$ISO_URL" 2>&1
if [ -s /tmp/proxmox.iso ]; then
losetup /dev/loop0 /tmp/proxmox.iso
echo "PXE: ISO on /dev/loop0"
else
echo "PXE: ERROR - download failed"
fi
fi
umount /dev 2>/dev/null
umount /sys 2>/dev/null
umount /proc 2>/dev/null
exec /init "$@"
`
func CreatePXEInitrd(origInitrdPath, isoPath, outputPath string) error {
func CreatePXEOverlay(outputPath string) error {
out, err := os.Create(outputPath)
if err != nil {
return fmt.Errorf("create output: %w", err)
return fmt.Errorf("create overlay: %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)
}
@@ -66,21 +79,6 @@ func writeCPIOEntry(w io.Writer, name string, data []byte, mode uint32, ino uint
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",