Add USB autoboot feature to PureBoot Basic

USB autoboot automatically boots to a USB flash drive if one is present
during boot.  This is intended for headless deployments as a method to
recover the installed operating system from USB without needing to
attach a display and keyboard.

USB autoboot can be controlled in config.user and the config GUI.

Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>

initrd/bin/config-gui.sh

@@ -32,6 +32,7 @@ while true; do
     # check current Restricted Boot Mode
     RESTRICTED_BOOT="$(load_config_value CONFIG_RESTRICTED_BOOT)"
     BASIC_NO_AUTOMATIC_DEFAULT="$(load_config_value CONFIG_BASIC_NO_AUTOMATIC_DEFAULT)"
+    BASIC_USB_AUTOBOOT="$(load_config_value CONFIG_BASIC_USB_AUTOBOOT)"
 
     dynamic_config_options=()
 
@@ -39,6 +40,7 @@ while true; do
         dynamic_config_options+=( \
             'P' " $(get_config_display_action "$BASIC_MODE") PureBoot Basic Mode" \
             'A' " $(get_inverted_config_display_action "$BASIC_NO_AUTOMATIC_DEFAULT") automatic default boot" \
+            'U' " $(get_config_display_action "$BASIC_USB_AUTOBOOT") USB automatic boot" \
         )
     else
         dynamic_config_options+=( \
@@ -362,6 +364,32 @@ while true; do
         fi
       fi
     ;;
+    "U" )
+      if [ "$BASIC_USB_AUTOBOOT" = "n" ]; then
+        if (whiptail --title 'Enable USB automatic boot?' \
+             --yesno "During boot, an attached bootable USB disk will be booted
+                    \nby default instead of the installed operating system.
+                    \n\nDo you want to proceed?" 0 80) then
+
+          set_config /etc/config.user "CONFIG_BASIC_USB_AUTOBOOT" "y"
+          combine_configs
+
+          whiptail --title 'Config change successful' \
+            --msgbox "USB automatic boot enabled;\nsave the config change and reboot for it to go into effect." 0 80
+        fi
+      else
+        if (whiptail --title 'Disable USB automatic boot?' \
+             --yesno "USB disks will no longer be booted by default.
+                    \n\nDo you want to proceed?" 0 80) then
+
+          set_config /etc/config.user "CONFIG_BASIC_USB_AUTOBOOT" "n"
+          combine_configs
+
+          whiptail --title 'Config change successful' \
+            --msgbox "USB automatic boot disabled;\nsave the config change and reboot for it to go into effect." 0 80
+        fi
+      fi
+    ;;
   esac
 
 done

initrd/bin/gui-init-basic

@@ -64,20 +64,11 @@ mount_boot()
 prompt_auto_default_boot()
 {
   TRACE "Under /bin/gui-init:prompt_auto_default_boot"
-
-  # save IFS before changing, restore after read
-  IFS_DEF=$IFS
-  IFS=''
-  first_pass=false
-
   echo -e "\n\n"
-  read -t $CONFIG_AUTO_BOOT_TIMEOUT -s -n 1 -p "Automatic boot in $CONFIG_AUTO_BOOT_TIMEOUT seconds unless interrupted by keypress... "
+  if pause_automatic_boot; then
-  if [[ $? -ne 0 ]]; then
-    IFS=$IFS_DEF
     echo -e "\n\nAttempting default boot...\n\n"
     attempt_default_boot
   fi
-  IFS=$IFS_DEF
 }
 
 show_main_menu()
@@ -194,6 +185,14 @@ attempt_default_boot()
 # gui-init-basic start
 TRACE "Under /bin/gui-init, start"
 
+# USB automatic boot (if configured) occurs before mounting /boot, this should
+# work even if no OS is installed
+if [ "$CONFIG_BASIC_USB_AUTOBOOT" = "y" ] && usb-autoboot.sh; then
+  # USB autoboot was offered and interrupted.  Don't offer the default boot,
+  # go to the menu.
+  skip_to_menu=true
+fi
+
 if ! detect_boot_device ; then
   # can't determine /boot device or no OS installed, 
   # so fall back to interactive selection

initrd/bin/usb-autoboot.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+set -o pipefail
+
+. /etc/functions
+. /etc/gui_functions
+
+# Automatically boot to a bootable USB medium if present.  This is for
+# unattended boot; there is no UI.
+# There are three possible results:
+# * Automatic boot occurs - script does not return (kexec happens)
+# * User interrupted automatic boot - script returns 0.  Skip normal boot and go
+#   to the boot menu (don't prompt for two automatic boots).
+# * No automatic boot was attempted - script returns nonzero.  Continue with
+#   normal automatic boot.
+
+# These may die for failure, nonzero exit is correct (USB boot wasn't possible)
+enable_usb
+enable_usb_storage
+
+mkdir -p /media
+
+parse_boot_options()
+{
+	BOOTDIR="$1"
+	for i in $(find "$BOOTDIR" -name '*.cfg'); do
+		kexec-parse-boot "$BOOTDIR" "$i"
+	done
+}
+
+# Look for any bootable USB medium.
+list_usb_storage >/tmp/usb-autoboot-usb-storage
+while read -u 4 -r USB_BLOCK_DEVICE; do
+	mount "$USB_BLOCK_DEVICE" /media || continue
+	USB_DEFAULT_BOOT="$(parse_boot_options /media | head -1)"
+	if [ -n "$USB_DEFAULT_BOOT" ]; then
+		# Boot automatically, unless the user interrupts.
+		echo -e "\n\n"
+		echo "Found bootable USB: $(echo "$USB_DEFAULT_BOOT" | cut -d '|' -f 1)"
+		if ! pause_automatic_boot; then
+			# User interrupted, go to boot menu
+			umount /media
+			exit 0
+		fi
+		echo -e "\n\nBooting from USB...\n\n"
+		kexec-boot -b /media -e "$USB_DEFAULT_BOOT"
+		# If kexec-boot returned, the boot obviously did not occur,
+		# return nonzero below so the normal OS boot will continue.
+	fi
+	umount /media
+done 4</tmp/usb-autoboot-usb-storage
+
+# No bootable USB medium found
+exit 1