Add netboot infrastructure: custom initramfs hooks, build scripts, iPXE configuration

initramfs/hooks/netboot

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+#!/bin/sh
+#
+# Add useful binaries to initrd for netboot HTTP root mounting
+#
+
+if [ "$1" = "prereqs" ]; then
+	echo "udev"
+	exit
+fi
+
+. /usr/share/initramfs-tools/hook-functions
+
+# Essential utilities for netboot - copy_exec handles dependencies automatically
+copy_exec "/usr/bin/wget"
+copy_exec "/usr/bin/curl"
+copy_exec "/usr/bin/unsquashfs"
+copy_exec "/usr/sbin/switch_root"
+
+# Useful tools for debugging
+copy_exec "/usr/bin/awk"
+copy_exec "/usr/bin/bash"
+copy_exec "/usr/bin/chmod"
+copy_exec "/usr/bin/file"
+copy_exec "/usr/bin/free"
+copy_exec "/usr/bin/grep"
+copy_exec "/usr/bin/gunzip"
+copy_exec "/usr/bin/gzip"
+copy_exec "/usr/bin/less"
+copy_exec "/usr/bin/lsblk"
+copy_exec "/usr/bin/mount"
+copy_exec "/usr/bin/readlink"
+copy_exec "/usr/bin/sed"
+copy_exec "/usr/bin/timeout"
+copy_exec "/usr/bin/touch"
+copy_exec "/usr/bin/vi"
+
+# Note: copy_exec automatically handles all shared library dependencies via ldd()
+# No need to manually copy libc or other libraries - copy_exec handles this

initramfs/initramfs.conf

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+#
+# initramfs.conf
+# Configuration file for mkinitramfs(8). See initramfs.conf(5).
+#
+
+#
+# MODULES: [ most | netboot | dep | list ]
+#
+# most - Add most filesystem and all harddrive drivers.
+#
+# dep - Try and guess which modules to load.
+#
+# netboot - Add the base modules, network modules, but skip block devices.
+#
+# list - Only include modules from the 'additional modules' list
+#
+
+MODULES=most
+
+#
+# BUSYBOX: [ y | n | auto ]
+#
+# Use busybox shell and utilities.  If set to n, klibc utilities will be used.
+# If set to auto (or unset), busybox will be used if installed and klibc will
+# be used otherwise.
+#
+
+BUSYBOX=auto
+
+#
+# COMPRESS: [ gzip | bzip2 | lz4 | lzma | lzop | xz | zstd ]
+#
+
+COMPRESS=gzip
+
+#
+# DEVICE: ...
+#
+# Specify a specific network interface, like eth0
+# Overridden by optional ip= or BOOTIF= bootarg
+#
+
+DEVICE=
+
+#
+# NFSROOT: [ auto | HOST:MOUNT ]
+#
+
+NFSROOT=auto
+
+#
+# RUNSIZE: ...
+#
+# The size of the /run tmpfs mount point, like 256M or 10%
+# Overridden by optional initramfs.runsize= bootarg
+#
+
+RUNSIZE=10%
+
+#
+# FSTYPE: ...
+#
+# The filesystem type(s) to support, or "auto" to use the current root
+# filesystem type
+#
+
+FSTYPE=auto
+
+# Disable hibernation
+RESUME=none

initramfs/modules

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+# List of modules that you want to include in your initramfs.
+# They will be loaded at boot time in the order below.
+#
+# Syntax:  module_name [args ...]
+#
+
+# Filesystem support
+nls_iso8859-1
+isofs
+ext4
+squashfs
+overlay
+
+# Network modules
+af_packet
+
+# RTL8125 network driver for 2.5GbE
+r8125

initramfs/scripts/netboot

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+#!/bin/sh
+
+# Import standard initramfs functions
+. /scripts/functions
+
+export PATH=/usr/bin:/usr/sbin:/bin:/sbin
+MOUNTPOINT=/root
+TMPFS_MOUNT=/mnt
+
+# Parse kernel command line for HTTP root
+parse_cmdline() {
+    for x in $(cat /proc/cmdline); do
+        case $x in
+            root=http://*)
+                export ROOT_URL="${x#root=}" ;;
+            rootfstype=*)
+                export ROOTFSTYPE="${x#rootfstype=}" ;;
+            overlayroot=*)
+                export OVERLAYROOT="${x#overlayroot=}" ;;
+            ip=*)
+                export BOOTIP="${x#ip=}" ;;
+            *)
+                : ;;
+        esac
+    done
+}
+
+mountroot() {
+    rc=1
+    parse_cmdline
+
+    if test -z "${ROOT_URL}"; then
+        log_failure_msg "No root URL defined (root=http://... not found)"
+        return ${rc}
+    fi
+
+    # Configure networking before attempting downloads
+    log_begin_msg "Configuring network"
+    modprobe af_packet || log_warning_msg "af_packet load failed"
+
+    # Load RTL8125 driver (already in module list but explicit load for debugging)
+    modprobe r8125 || log_warning_msg "r8125 driver load failed, may use generic driver"
+
+    configure_networking
+    udevadm trigger
+    timeout 30 udevadm settle || log_warning_msg "udevadm settle timed out"
+    export DEVICE
+    log_end_msg
+
+    # Validate networking is up
+    INTERFACE_UP=0
+    for iface in $(ip link show | grep "^[0-9]" | awk -F: '{print $2}' | tr -d ' '); do
+        if ip addr show "$iface" | grep -q "inet "; then
+            INTERFACE_UP=1
+            log_begin_msg "Interface $iface has IP address"
+            ip addr show "$iface" | grep "inet " | awk '{print $2}'
+            break
+        fi
+    done
+
+    if [ $INTERFACE_UP -eq 0 ]; then
+        log_failure_msg "No network interface obtained an IP address"
+        return ${rc}
+    fi
+
+    # Extract filename from URL
+    FILE_NAME=$(basename "${ROOT_URL}")
+    FILE_PATH="/${FILE_NAME}"
+
+    # Download the root filesystem with retries and timeouts
+    log_begin_msg "Downloading root filesystem from ${ROOT_URL}"
+    if wget --timeout=30 --tries=3 --waitretry=5 \
+            --progress=dot:mega \
+            "${ROOT_URL}" -O "${FILE_PATH}"; then
+        log_end_msg
+    else
+        log_failure_msg "Failed to download from ${ROOT_URL} after retries"
+        rm -f "${FILE_PATH}"
+        return ${rc}
+    fi
+
+    # Verify the downloaded file is a valid SquashFS
+    if ! file "${FILE_PATH}" | grep -q "Squash"; then
+        log_failure_msg "Downloaded file is not a valid SquashFS image"
+        rm -f "${FILE_PATH}"
+        return ${rc}
+    fi
+
+    # Handle SquashFS images with overlay
+    if echo "${FILE_NAME}" | grep -q squashfs; then
+        log_begin_msg "Setting up SquashFS with overlay"
+
+        # Mount read-only SquashFS
+        if ! mount -t squashfs "${FILE_PATH}" "${MOUNTPOINT}" -o ro; then
+            log_failure_msg "Failed to mount SquashFS at ${MOUNTPOINT}"
+            rm -f "${FILE_PATH}"
+            return ${rc}
+        fi
+        log_begin_msg "SquashFS mounted at ${MOUNTPOINT}"
+        log_end_msg
+
+        # Setup overlay if requested
+        if [ -n "${OVERLAYROOT}" ]; then
+            log_begin_msg "Mounting ${OVERLAYROOT} for overlay"
+
+            # Create tmpfs for upper and work directories
+            if ! mount -o size=2G -t "${OVERLAYROOT}" tmpfs_overlay "${TMPFS_MOUNT}"; then
+                log_failure_msg "Failed to mount tmpfs for overlay"
+                umount "${MOUNTPOINT}"
+                rm -f "${FILE_PATH}"
+                return ${rc}
+            fi
+
+            # Create overlay structure
+            mkdir -p "${TMPFS_MOUNT}/upper" "${TMPFS_MOUNT}/work"
+
+            # Mount overlay combining read-only lower + writable upper
+            if ! mount -t overlay \
+                    -o "lowerdir=${MOUNTPOINT},upperdir=${TMPFS_MOUNT}/upper,workdir=${TMPFS_MOUNT}/work" \
+                    overlay_root "${MOUNTPOINT}"; then
+                log_failure_msg "Failed to mount overlay filesystem"
+                umount "${TMPFS_MOUNT}"
+                umount "${MOUNTPOINT}"
+                rm -f "${FILE_PATH}"
+                return ${rc}
+            fi
+
+            log_end_msg
+            log_begin_msg "Overlay mounted successfully"
+            log_end_msg
+
+            # Clean up downloaded image as it's now mounted
+            rm -f "${FILE_PATH}"
+            rc=0
+        else
+            # Direct SquashFS mount without overlay
+            log_begin_msg "Mounted SquashFS without overlay"
+            log_end_msg
+            rc=0
+        fi
+    else
+        log_failure_msg "Unknown filesystem type: ${FILE_NAME}"
+        rm -f "${FILE_PATH}"
+    fi
+
+    return ${rc}
+}