feat(extensions): add netboot extension for TFTP+NFS diskless boot

config/templates/nfs-boot.cmd.template

@@ -7,27 +7,71 @@
 setenv net_setup "ip=dhcp"
 
 # for static configuration see documentation
-# https://github.com/torvalds/linux/blob/master/Documentation/admin-guide/nfs/nfsroot.rst
+# https://www.kernel.org/doc/Documentation/admin-guide/nfs/nfsroot.rst
 # setenv net_setup "ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns0-ip>:<dns1-ip>"
 
-# you may need to add extra kernel arguments specific to your device
-setenv bootargs "console=tty1 console=ttyS0,115200 root=/dev/nfs ${net_setup} rw rootflags=noatime disp.screen0_output_mode=1920x1080p60 panic=10 consoleblank=0 enforcing=0 loglevel=6"
+# No hardcoded `console=`: kernels resolve the console from the DTB's
+# /chosen/stdout-path. Hardcoding a baud rate here breaks boards whose
+# UART runs at non-115200 speeds (e.g. helios64 @ 1500000).
+setenv bootargs "root=/dev/nfs ${net_setup} rw rootwait earlycon panic=10 loglevel=6"
 
-if test -n ${nfs_root}; then
+if test -n "${nfs_root}"; then
 	setenv bootargs "${bootargs} nfsroot=${nfs_root}"
 fi
 
-if ext4load mmc 0 0x00000000 .next || fatload mmc 0 0x00000000 .next; then
-	ext4load mmc 0 ${fdt_addr_r} /dtb/${fdtfile} || fatload mmc 0 ${fdt_addr_r} /dtb/${fdtfile}
-	ext4load mmc 0 ${kernel_addr_r} zImage || fatload mmc 0 ${kernel_addr_r} zImage
-	ext4load mmc 0 ${ramdisk_addr_r} uInitrd || fatload mmc 0 ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
-	setenv fdt_high ffffffff
-	bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}
+# Load kernel + DTB + initrd from the active distro boot partition.
+# devtype/devnum/distro_bootpart are set by U-Boot's bootflow scanner
+# before this script runs. Boards that source boot.scr directly (legacy
+# sunxi without distro_bootcmd, etc.) have these unset — fall back to
+# the historical "mmc 0:1" so the existing ROOTFS_TYPE=nfs path keeps
+# working there.
+test -n "${devtype}" || setenv devtype mmc
+test -n "${devnum}" || setenv devnum 0
+test -n "${distro_bootpart}" || setenv distro_bootpart 1
+setenv boot_dev "${devtype} ${devnum}:${distro_bootpart}"
+
+# Probe mainline marker: mainline rootfs has /boot/.next, legacy sunxi (pre-DT)
+# does not — it ships script.bin in place of a DTB.
+if load ${boot_dev} ${fdt_addr_r} .next; then
+	# Mainline: real DTB, arm64 flat Image or compressed zImage.
+	# Some boards (TI K3, BeagleBone) keep fdtfile with a .dts suffix; the
+	# tree installs the compiled .dtb, so we need to normalize before loading.
+	setenv dtb_name "${fdtfile}"
+	# U-Boot setexpr.s sub takes `<regex> <substitute>` — the target is implicit
+	# (the named variable itself), which is both read and written in place.
+	setexpr.s dtb_name sub "\\.dts\$" ".dtb"
+	if load ${boot_dev} ${fdt_addr_r} dtb/${dtb_name}; then
+		true
+	else
+		echo "FATAL: failed to load DTB dtb/${dtb_name} (fdtfile=${fdtfile})"
+		reset
+	fi
+	load ${boot_dev} ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
+	if load ${boot_dev} ${kernel_addr_r} Image; then
+		booti ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}
+	elif load ${boot_dev} ${kernel_addr_r} zImage; then
+		setenv fdt_high ffffffff
+		bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}
+	else
+		echo "FATAL: failed to load kernel (neither Image nor zImage)"
+		reset
+	fi
 else
-	ext4load mmc 0 ${fdt_addr_r} script.bin || fatload mmc 0 ${fdt_addr_r} script.bin
-	ext4load mmc 0 ${kernel_addr_r} zImage || fatload mmc 0 ${kernel_addr_r} zImage
-	ext4load mmc 0 ${ramdisk_addr_r} uInitrd || fatload mmc 0 ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
-	bootz ${kernel_addr_r} ${ramdisk_addr_r}
+	# Legacy sunxi (pre-mainline): script.bin substitutes for DTB, zImage only,
+	# bootz is called without the fdt argument.
+	if load ${boot_dev} ${fdt_addr_r} script.bin; then
+		true
+	else
+		echo "FATAL: no mainline (.next) and no legacy script.bin"
+		reset
+	fi
+	load ${boot_dev} ${ramdisk_addr_r} uInitrd || setenv ramdisk_addr_r "-"
+	if load ${boot_dev} ${kernel_addr_r} zImage; then
+		bootz ${kernel_addr_r} ${ramdisk_addr_r}
+	else
+		echo "FATAL: failed to load zImage (legacy)"
+		reset
+	fi
 fi
 
 # Recompile with:

extensions/netboot/files/dhcpcd-hooks/71-netboot-rootpath

@@ -0,0 +1,27 @@
+#!/bin/sh
+# Fix ROOTSERVER in /run/net-${interface}.conf for nfsroot=<path> (path-only) boots.
+#
+# The standard 70-net-conf hook sets ROOTSERVER='${new_routers}' (default
+# gateway).  The kernel's own IP-Config (ip=dhcp) correctly resolves the boot
+# server from DHCP siaddr and records it as "bootserver" in /proc/net/pnp.
+# Appending ROOTSERVER from there overrides the gateway value; shell-source
+# semantics in /scripts/nfs pick the last assignment.
+#
+# Installed by the Armbian `netboot` extension.
+
+if ${if_configured?} && ${if_up?} && [ "${protocol-}" = dhcp ] \
+	&& [ -f "/run/net-${interface?}.conf" ]; then
+
+	# Read boot server from kernel IP-Config — set from DHCP siaddr.
+	# /proc/net/pnp is only populated when the kernel handles DHCP itself
+	# (ip=dhcp in cmdline); if it is absent or has no valid bootserver entry
+	# we clear ROOTSERVER explicitly so nfs-mount fails fast rather than
+	# silently trying the default gateway written by 70-net-conf.
+	bootserver=$(grep '^bootserver ' /proc/net/pnp 2>/dev/null | cut -d' ' -f2)
+	if [ -n "$bootserver" ] && [ "$bootserver" != "0.0.0.0" ]; then
+		printf "ROOTSERVER='%s'\n" "$bootserver" >> "/run/net-${interface}.conf"
+	else
+		printf '71-netboot-rootpath: bootserver not found in /proc/net/pnp, clearing ROOTSERVER\n' >&2
+		printf "ROOTSERVER=''\n" >> "/run/net-${interface}.conf"
+	fi
+fi

extensions/netboot/files/initramfs-hooks/netboot-rootpath

@@ -0,0 +1,26 @@
+#!/bin/sh
+# Initramfs hook: include 71-netboot-rootpath in the dhcpcd hooks dir of the
+# generated initramfs. That hook overrides ROOTSERVER in
+# /run/net-${interface}.conf with the boot server from /proc/net/pnp so the
+# initramfs nfs-mount script does not fall back to the default gateway.
+# Companion of the Armbian `netboot` extension.
+
+set -e
+
+PREREQ=""
+case "$1" in
+	prereqs) echo "$PREREQ"; exit 0 ;;
+esac
+
+. /usr/share/initramfs-tools/hook-functions
+
+# Mirror the destination directory choice from the upstream `dhcpcd` hook
+# (depends on whether dhcpcd ships its hooks in /usr/lib/dhcpcd or /usr/libexec).
+if [ -e /usr/lib/dhcpcd/dhcpcd-run-hooks ]; then
+	dhcpcd_dir=/usr/lib/dhcpcd
+else
+	dhcpcd_dir=/usr/libexec
+fi
+
+copy_file config /usr/share/initramfs-tools/dhcpcd-hooks/71-netboot-rootpath \
+	"${dhcpcd_dir}/dhcpcd-hooks/71-netboot-rootpath"

extensions/netboot/files/initramfs-scripts/init-premount/zz-netboot-watchdog

@@ -0,0 +1,24 @@
+#!/bin/sh
+PREREQ=""
+prereqs() { echo "$PREREQ"; }
+case $1 in
+    prereqs) prereqs; exit 0 ;;
+esac
+
+# Only arm on NFS root boots.
+grep -q "root=/dev/nfs" /proc/cmdline || exit 0
+
+# Trigger SysRq-B (immediate reboot, not a kernel panic — different kernel path,
+# reboot via PSCI on arm64) after 10 min if NFS root mount hangs.
+# nfs-bottom/zz-netboot-watchdog-cancel kills this on successful mount.
+(
+    sleep 600
+    echo "netboot-watchdog: 10 min elapsed, forcing reboot" > /dev/kmsg 2>/dev/null
+    # Force-enable SysRq before triggering. If kernel.sysrq is 0 at runtime
+    # (hardened image, sysctl override, etc.), `echo b` writes succeed at the
+    # shell level but are no-ops in the kernel — the watchdog would log its
+    # message and then hang. Setting `1` enables the full command set.
+    echo 1 > /proc/sys/kernel/sysrq 2>/dev/null || true
+    echo b > /proc/sysrq-trigger
+) &
+echo $! > /run/netboot-watchdog.pid

extensions/netboot/files/initramfs-scripts/nfs-bottom/zz-netboot-watchdog-cancel

@@ -0,0 +1,21 @@
+#!/bin/sh
+PREREQ=""
+prereqs() { echo "$PREREQ"; }
+case $1 in
+    prereqs) prereqs; exit 0 ;;
+esac
+
+# Cancel the NFS watchdog started by init-premount/zz-netboot-watchdog.
+# Validate the pidfile content before signalling: a stale or corrupted file
+# (truncated, non-numeric, or PID 1 from kernel/init) must not produce an
+# unintended kill. Only proceed for a numeric PID strictly greater than 1.
+if [ -f /run/netboot-watchdog.pid ]; then
+    read -r watchdog_pid < /run/netboot-watchdog.pid 2>/dev/null || watchdog_pid=""
+    case "${watchdog_pid}" in
+        '' | *[!0-9]*) ;;
+        *)
+            [ "${watchdog_pid}" -gt 1 ] && kill "${watchdog_pid}" 2> /dev/null
+            ;;
+    esac
+    rm -f /run/netboot-watchdog.pid
+fi