firmware/2lib/2ui.c - mirrors/cros/chromiumos/platform/vboot_reference - Git at Google

 /* Copyright 2020 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * User interfaces for developer and recovery mode menus.
  */

 #include "2api.h"
 #include "2common.h"
 #include "2misc.h"
 #include "2nvstorage.h"
 #include "2return_codes.h"
 #include "2secdata.h"
 #include "2ui.h"
 #include "2ui_private.h"
 #include "vboot_api.h"  /* For VB_SHUTDOWN_REQUEST_POWER_BUTTON */
 #include "vboot_kernel.h"
 #include "vboot_ui_legacy.h"  /* TODO(b/144969088): VbDisplayDebugInfo */

 #define KEY_DELAY_MS 20  /* Delay between key scans in UI loops */

 /*****************************************************************************/
 /* Utility functions */

 /**
  * Check GBB flags against VbExIsShutdownRequested() shutdown request,
  * and check for VB_BUTTON_POWER_SHORT_PRESS key, to determine if a
  * shutdown is required.
  *
  * @param ui		UI context pointer
  * @return VB2_REQUEST_SHUTDOWN if shutdown needed, or VB2_REQUEST_UI_CONTINUE
  */
 vb2_error_t check_shutdown_request(struct vb2_ui_context *ui)
 {
 	struct vb2_gbb_header *gbb = vb2_get_gbb(ui->ctx);
 	uint32_t shutdown_request = VbExIsShutdownRequested();

 	/*
 	 * Ignore power button push until after we have seen it released.
 	 * This avoids shutting down immediately if the power button is still
 	 * being held on startup. After we've recognized a valid power button
 	 * push then don't report the event until after the button is released.
 	 */
 	if (shutdown_request & VB_SHUTDOWN_REQUEST_POWER_BUTTON) {
 		shutdown_request &= ~VB_SHUTDOWN_REQUEST_POWER_BUTTON;
 		if (ui->power_button == VB2_POWER_BUTTON_RELEASED)
 			ui->power_button = VB2_POWER_BUTTON_PRESSED;
 	} else {
 		if (ui->power_button == VB2_POWER_BUTTON_PRESSED)
 			shutdown_request |= VB_SHUTDOWN_REQUEST_POWER_BUTTON;
 		ui->power_button = VB2_POWER_BUTTON_RELEASED;
 	}

 	if (ui->key == VB_BUTTON_POWER_SHORT_PRESS)
 		shutdown_request |= VB_SHUTDOWN_REQUEST_POWER_BUTTON;

 	/* If desired, ignore shutdown request due to lid closure. */
 	if (gbb->flags & VB2_GBB_FLAG_DISABLE_LID_SHUTDOWN)
 		shutdown_request &= ~VB_SHUTDOWN_REQUEST_LID_CLOSED;

 	/*
 	 * In detachables, disable shutdown due to power button.
 	 * It is used for menu selection instead.
 	 */
 	if (DETACHABLE)
 		shutdown_request &= ~VB_SHUTDOWN_REQUEST_POWER_BUTTON;

 	if (shutdown_request)
 		return VB2_REQUEST_SHUTDOWN;

 	return VB2_REQUEST_UI_CONTINUE;
 }

 /*****************************************************************************/
 /* Error action functions */

 vb2_error_t error_exit_action(struct vb2_ui_context *ui)
 {
 	/*
 	 * If an error message is currently shown on the screen, any
 	 * key press clears that error.  Unset the key so that it is
 	 * not processed by other action functions.
 	 */
 	if (ui->key && ui->error_code != VB2_UI_ERROR_NONE) {
 		ui->error_code = VB2_UI_ERROR_NONE;
 		ui->key = 0;
 	}
 	return VB2_REQUEST_UI_CONTINUE;
 }

 /*****************************************************************************/
 /* Menu navigation functions */

 const struct vb2_menu *get_menu(struct vb2_ui_context *ui)
 {
 	const struct vb2_menu *menu;
 	static const struct vb2_menu empty_menu = {
 		.num_items = 0,
 		.items = NULL,
 	};
 	if (ui->state->screen->get_menu) {
 		menu = ui->state->screen->get_menu(ui);
 		return menu ? menu : &empty_menu;
 	} else {
 		return &ui->state->screen->menu;
 	}
 }

 vb2_error_t menu_navigation_action(struct vb2_ui_context *ui)
 {
 	uint32_t key = ui->key;

 	/* Map detachable button presses for simplicity. */
 	if (DETACHABLE) {
 		if (key == VB_BUTTON_VOL_UP_SHORT_PRESS)
 			key = VB_KEY_UP;
 		else if (key == VB_BUTTON_VOL_DOWN_SHORT_PRESS)
 			key = VB_KEY_DOWN;
 		else if (key == VB_BUTTON_POWER_SHORT_PRESS)
 			key = VB_KEY_ENTER;
 	}

 	switch (key) {
 	case VB_KEY_UP:
 		return vb2_ui_menu_prev(ui);
 	case VB_KEY_DOWN:
 		return vb2_ui_menu_next(ui);
 	case VB_KEY_ENTER:
 		return vb2_ui_menu_select(ui);
 	case VB_KEY_ESC:
 		return vb2_ui_screen_back(ui);
 	default:
 		if (key != 0)
 			VB2_DEBUG("Pressed key %#x, trusted? %d\n",
 				  ui->key, ui->key_trusted);
 	}

 	return VB2_REQUEST_UI_CONTINUE;
 }

 vb2_error_t vb2_ui_menu_prev(struct vb2_ui_context *ui)
 {
 	int item;

 	if (!DETACHABLE && ui->key == VB_BUTTON_VOL_UP_SHORT_PRESS)
 		return VB2_REQUEST_UI_CONTINUE;

 	item = ui->state->selected_item - 1;
 	while (item >= 0 &&
 	       ((1 << item) & ui->state->disabled_item_mask))
 		item--;
 	/* Only update if item is valid */
 	if (item >= 0)
 		ui->state->selected_item = item;

 	return VB2_REQUEST_UI_CONTINUE;
 }

 vb2_error_t vb2_ui_menu_next(struct vb2_ui_context *ui)
 {
 	int item;
 	const struct vb2_menu *menu;

 	if (!DETACHABLE && ui->key == VB_BUTTON_VOL_DOWN_SHORT_PRESS)
 		return VB2_REQUEST_UI_CONTINUE;

 	menu = get_menu(ui);
 	item = ui->state->selected_item + 1;
 	while (item < menu->num_items &&
 	       ((1 << item) & ui->state->disabled_item_mask))
 		item++;
 	/* Only update if item is valid */
 	if (item < menu->num_items)
 		ui->state->selected_item = item;

 	return VB2_REQUEST_UI_CONTINUE;
 }

 vb2_error_t vb2_ui_menu_select(struct vb2_ui_context *ui)
 {
 	const struct vb2_menu *menu;
 	const struct vb2_menu_item *menu_item;

 	if (!DETACHABLE && ui->key == VB_BUTTON_POWER_SHORT_PRESS)
 		return VB2_REQUEST_UI_CONTINUE;

 	menu = get_menu(ui);
 	if (menu->num_items == 0)
 		return VB2_REQUEST_UI_CONTINUE;

 	menu_item = &menu->items[ui->state->selected_item];

 	if (menu_item->action) {
 		VB2_DEBUG("Menu item <%s> run action\n", menu_item->text);
 		return menu_item->action(ui);
 	} else if (menu_item->target) {
 		VB2_DEBUG("Menu item <%s> to target screen %#x\n",
 			  menu_item->text, menu_item->target);
 		return vb2_ui_screen_change(ui, menu_item->target);
 	}

 	VB2_DEBUG("Menu item <%s> no action or target screen\n",
 		  menu_item->text);
 	return VB2_REQUEST_UI_CONTINUE;
 }

 /*****************************************************************************/
 /* Screen navigation functions */

 vb2_error_t vb2_ui_screen_back(struct vb2_ui_context *ui)
 {
 	struct vb2_screen_state *tmp;

 	if (ui->state && ui->state->prev) {
 		tmp = ui->state->prev;
 		free(ui->state);
 		ui->state = tmp;
 	} else {
 		VB2_DEBUG("ERROR: No previous screen; ignoring\n");
 	}

 	return VB2_REQUEST_UI_CONTINUE;
 }

 static vb2_error_t default_screen_init(struct vb2_ui_context *ui)
 {
 	const struct vb2_menu *menu = get_menu(ui);
 	ui->state->selected_item = 0;
 	if (menu->num_items > 1 && menu->items[0].is_language_select)
 		ui->state->selected_item = 1;
 	return VB2_REQUEST_UI_CONTINUE;
 }

 vb2_error_t vb2_ui_screen_change(struct vb2_ui_context *ui, enum vb2_screen id)
 {
 	const struct vb2_screen_info *new_screen_info;
 	struct vb2_screen_state *cur_state;
 	int state_exists = 0;

 	new_screen_info = vb2_get_screen_info(id);
 	if (new_screen_info == NULL) {
 		VB2_DEBUG("ERROR: Screen entry %#x not found; ignoring\n", id);
 		return VB2_REQUEST_UI_CONTINUE;
 	}

 	/* Check to see if the screen state already exists in our stack. */
 	cur_state = ui->state;
 	while (cur_state != NULL) {
 		if (cur_state->screen->id == id) {
 			state_exists = 1;
 			break;
 		}
 		cur_state = cur_state->prev;
 	}

 	if (state_exists) {
 		/* Pop until the requested screen is at the top of stack. */
 		while (ui->state->screen->id != id) {
 			cur_state = ui->state;
 			ui->state = cur_state->prev;
 			free(cur_state);
 		}
 	} else {
 		/* Allocate the requested screen on top of the stack. */
 		cur_state = malloc(sizeof(*ui->state));
 		memset(cur_state, 0, sizeof(*ui->state));
 		if (cur_state == NULL) {
 			VB2_DEBUG("WARNING: malloc failed; ignoring\n");
 			return VB2_REQUEST_UI_CONTINUE;
 		}
 		cur_state->prev = ui->state;
 		cur_state->screen = new_screen_info;
 		ui->state = cur_state;
 		if (ui->state->screen->init)
 			return ui->state->screen->init(ui);
 		else
 			return default_screen_init(ui);
 	}

 	return VB2_REQUEST_UI_CONTINUE;
 }

 /*****************************************************************************/
 /* Core UI loop */

 vb2_error_t ui_loop(struct vb2_context *ctx, enum vb2_screen root_screen_id,
 		    vb2_error_t (*global_action)(struct vb2_ui_context *ui))
 {
 	struct vb2_ui_context ui;
 	struct vb2_screen_state prev_state;
 	int prev_disable_timer;
 	enum vb2_ui_error prev_error_code;
 	const struct vb2_menu *menu;
 	const struct vb2_screen_info *root_info;
 	uint32_t key_flags;
 	vb2_error_t rv;

 	memset(&ui, 0, sizeof(ui));
 	ui.ctx = ctx;
 	root_info = vb2_get_screen_info(root_screen_id);
 	if (root_info == NULL)
 		VB2_DIE("Root screen not found.\n");
 	ui.locale_id = vb2_nv_get(ctx, VB2_NV_LOCALIZATION_INDEX);
 	rv = vb2_ui_screen_change(&ui, root_screen_id);
 	if (rv != VB2_REQUEST_UI_CONTINUE)
 		return rv;
 	memset(&prev_state, 0, sizeof(prev_state));
 	prev_disable_timer = 0;
 	prev_error_code = VB2_UI_ERROR_NONE;

 	while (1) {
 		/* Draw if there are state changes. */
 		if (memcmp(&prev_state, ui.state, sizeof(*ui.state)) ||
 		    /* We want to redraw when timer is disabled. */
 		    prev_disable_timer != ui.disable_timer ||
 		    /* We want to redraw/beep on a transition. */
 		    prev_error_code != ui.error_code) {

 			menu = get_menu(&ui);
 			VB2_DEBUG("<%s> menu item <%s>\n",
 				  ui.state->screen->name,
 				  menu->num_items ?
 				  menu->items[ui.state->selected_item].text :
 				  "null");
 			vb2ex_display_ui(ui.state->screen->id, ui.locale_id,
 					 ui.state->selected_item,
 					 ui.state->disabled_item_mask,
 					 ui.disable_timer,
 					 ui.error_code);
 			if (ui.error_beep) {
 				vb2ex_beep(250, 400);
 				ui.error_beep = 0;
 			}

 			/* Update prev variables. */
 			memcpy(&prev_state, ui.state, sizeof(*ui.state));
 			prev_disable_timer = ui.disable_timer;
 			prev_error_code = ui.error_code;
 		}

 		/* Grab new keyboard input. */
 		ui.key = VbExKeyboardReadWithFlags(&key_flags);
 		ui.key_trusted = !!(key_flags & VB_KEY_FLAG_TRUSTED_KEYBOARD);

 		/* Check for shutdown request. */
 		rv = check_shutdown_request(&ui);
 		if (rv != VB2_REQUEST_UI_CONTINUE) {
 			VB2_DEBUG("Shutdown requested!\n");
 			return rv;
 		}

 		/* Check if we need to exit an error box. */
 		rv = error_exit_action(&ui);
 		if (rv != VB2_REQUEST_UI_CONTINUE)
 			return rv;

 		/* Run screen action. */
 		if (ui.state->screen->action) {
 			rv = ui.state->screen->action(&ui);
 			if (rv != VB2_REQUEST_UI_CONTINUE)
 				return rv;
 		}

 		/* Run menu navigation action. */
 		rv = menu_navigation_action(&ui);
 		if (rv != VB2_REQUEST_UI_CONTINUE)
 			return rv;

 		/* Run global action function if available. */
 		if (global_action) {
 			rv = global_action(&ui);
 			if (rv != VB2_REQUEST_UI_CONTINUE)
 				return rv;
 		}

 		/* Delay. */
 		vb2ex_msleep(KEY_DELAY_MS);
 	}

 	return VB2_SUCCESS;
 }

 /*****************************************************************************/
 /* Developer mode */

 vb2_error_t vb2_developer_menu(struct vb2_context *ctx)
 {
 	return ui_loop(ctx, VB2_SCREEN_DEVELOPER_MODE, developer_action);
 }

 vb2_error_t developer_action(struct vb2_ui_context *ui)
 {
 	/* Developer mode keyboard shortcuts */
 	if (ui->key == VB_KEY_CTRL('S'))
 		return vb2_ui_screen_change(ui, VB2_SCREEN_DEVELOPER_TO_NORM);
 	if (ui->key == VB_KEY_CTRL('U') ||
 	    (DETACHABLE && ui->key == VB_BUTTON_VOL_UP_LONG_PRESS))
 		return vb2_ui_developer_mode_boot_external_action(ui);
 	if (ui->key == VB_KEY_CTRL('D') ||
 	    (DETACHABLE && ui->key == VB_BUTTON_VOL_DOWN_LONG_PRESS))
 		return vb2_ui_developer_mode_boot_internal_action(ui);

 	/* TODO(b/144969088): Re-implement as debug info screen. */
 	if (ui->key == '\t')
 		VbDisplayDebugInfo(ui->ctx);

 	return VB2_REQUEST_UI_CONTINUE;
 }

 /*****************************************************************************/
 /* Broken recovery */

 vb2_error_t vb2_broken_recovery_menu(struct vb2_context *ctx)
 {
 	return ui_loop(ctx, VB2_SCREEN_RECOVERY_BROKEN, broken_recovery_action);
 }

 vb2_error_t broken_recovery_action(struct vb2_ui_context *ui)
 {
 	/* TODO(b/144969088): Re-implement as debug info screen. */
 	if (ui->key == '\t')
 		VbDisplayDebugInfo(ui->ctx);

 	return VB2_REQUEST_UI_CONTINUE;
 }

 /*****************************************************************************/
 /* Manual recovery */

 vb2_error_t vb2_manual_recovery_menu(struct vb2_context *ctx)
 {
 	return ui_loop(ctx, VB2_SCREEN_RECOVERY_SELECT, manual_recovery_action);
 }

 vb2_error_t manual_recovery_action(struct vb2_ui_context *ui)
 {
 	/* See if we have a recovery kernel available yet. */
 	vb2_error_t rv = VbTryLoadKernel(ui->ctx, VB_DISK_FLAG_REMOVABLE);
 	if (rv == VB2_SUCCESS)
 		return rv;

 	/* If disk validity state changed, switch to appropriate screen. */
 	if (ui->recovery_rv != rv) {
 		VB2_DEBUG("Recovery VbTryLoadKernel %#x --> %#x\n",
 			  ui->recovery_rv, rv);
 		ui->recovery_rv = rv;
 		return vb2_ui_screen_change(ui,
 					    rv == VB2_ERROR_LK_NO_DISK_FOUND ?
 					    VB2_SCREEN_RECOVERY_SELECT :
 					    VB2_SCREEN_RECOVERY_INVALID);
 	}

 	/* Manual recovery keyboard shortcuts */
 	if (ui->key == VB_KEY_CTRL('D') ||
 	    (DETACHABLE && ui->key == VB_BUTTON_VOL_UP_DOWN_COMBO_PRESS))
 		return vb2_ui_screen_change(ui, VB2_SCREEN_RECOVERY_TO_DEV);

 	/* TODO(b/144969088): Re-implement as debug info screen. */
 	if (ui->key == '\t')
 		VbDisplayDebugInfo(ui->ctx);

 	return VB2_REQUEST_UI_CONTINUE;
 }
	/* Copyright 2020 The Chromium OS Authors. All rights reserved.
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*
	* User interfaces for developer and recovery mode menus.
	*/

	#include "2api.h"
	#include "2common.h"
	#include "2misc.h"
	#include "2nvstorage.h"
	#include "2return_codes.h"
	#include "2secdata.h"
	#include "2ui.h"
	#include "2ui_private.h"
	#include "vboot_api.h" /* For VB_SHUTDOWN_REQUEST_POWER_BUTTON */
	#include "vboot_kernel.h"
	#include "vboot_ui_legacy.h" /* TODO(b/144969088): VbDisplayDebugInfo */

	#define KEY_DELAY_MS 20 /* Delay between key scans in UI loops */

	/*****************************************************************************/
	/* Utility functions */

	/**
	* Check GBB flags against VbExIsShutdownRequested() shutdown request,
	* and check for VB_BUTTON_POWER_SHORT_PRESS key, to determine if a
	* shutdown is required.
	*
	* @param ui UI context pointer
	* @return VB2_REQUEST_SHUTDOWN if shutdown needed, or VB2_REQUEST_UI_CONTINUE
	*/
	vb2_error_t check_shutdown_request(struct vb2_ui_context *ui)
	{
	struct vb2_gbb_header *gbb = vb2_get_gbb(ui->ctx);
	uint32_t shutdown_request = VbExIsShutdownRequested();

	/*
	* Ignore power button push until after we have seen it released.
	* This avoids shutting down immediately if the power button is still
	* being held on startup. After we've recognized a valid power button
	* push then don't report the event until after the button is released.
	*/
	if (shutdown_request & VB_SHUTDOWN_REQUEST_POWER_BUTTON) {
	shutdown_request &= ~VB_SHUTDOWN_REQUEST_POWER_BUTTON;
	if (ui->power_button == VB2_POWER_BUTTON_RELEASED)
	ui->power_button = VB2_POWER_BUTTON_PRESSED;
	} else {
	if (ui->power_button == VB2_POWER_BUTTON_PRESSED)
	shutdown_request \|= VB_SHUTDOWN_REQUEST_POWER_BUTTON;
	ui->power_button = VB2_POWER_BUTTON_RELEASED;
	}

	if (ui->key == VB_BUTTON_POWER_SHORT_PRESS)
	shutdown_request \|= VB_SHUTDOWN_REQUEST_POWER_BUTTON;

	/* If desired, ignore shutdown request due to lid closure. */
	if (gbb->flags & VB2_GBB_FLAG_DISABLE_LID_SHUTDOWN)
	shutdown_request &= ~VB_SHUTDOWN_REQUEST_LID_CLOSED;

	/*
	* In detachables, disable shutdown due to power button.
	* It is used for menu selection instead.
	*/
	if (DETACHABLE)
	shutdown_request &= ~VB_SHUTDOWN_REQUEST_POWER_BUTTON;

	if (shutdown_request)
	return VB2_REQUEST_SHUTDOWN;

	return VB2_REQUEST_UI_CONTINUE;
	}

	/*****************************************************************************/
	/* Error action functions */

	vb2_error_t error_exit_action(struct vb2_ui_context *ui)
	{
	/*
	* If an error message is currently shown on the screen, any
	* key press clears that error. Unset the key so that it is
	* not processed by other action functions.
	*/
	if (ui->key && ui->error_code != VB2_UI_ERROR_NONE) {
	ui->error_code = VB2_UI_ERROR_NONE;
	ui->key = 0;
	}
	return VB2_REQUEST_UI_CONTINUE;
	}

	/*****************************************************************************/
	/* Menu navigation functions */

	const struct vb2_menu get_menu(struct vb2_ui_context ui)
	{
	const struct vb2_menu *menu;
	static const struct vb2_menu empty_menu = {
	.num_items = 0,
	.items = NULL,
	};
	if (ui->state->screen->get_menu) {
	menu = ui->state->screen->get_menu(ui);
	return menu ? menu : &empty_menu;
	} else {
	return &ui->state->screen->menu;
	}
	}

	vb2_error_t menu_navigation_action(struct vb2_ui_context *ui)
	{
	uint32_t key = ui->key;

	/* Map detachable button presses for simplicity. */
	if (DETACHABLE) {
	if (key == VB_BUTTON_VOL_UP_SHORT_PRESS)
	key = VB_KEY_UP;
	else if (key == VB_BUTTON_VOL_DOWN_SHORT_PRESS)
	key = VB_KEY_DOWN;
	else if (key == VB_BUTTON_POWER_SHORT_PRESS)
	key = VB_KEY_ENTER;
	}

	switch (key) {
	case VB_KEY_UP:
	return vb2_ui_menu_prev(ui);
	case VB_KEY_DOWN:
	return vb2_ui_menu_next(ui);
	case VB_KEY_ENTER:
	return vb2_ui_menu_select(ui);
	case VB_KEY_ESC:
	return vb2_ui_screen_back(ui);
	default:
	if (key != 0)
	VB2_DEBUG("Pressed key %#x, trusted? %d\n",
	ui->key, ui->key_trusted);
	}

	return VB2_REQUEST_UI_CONTINUE;
	}

	vb2_error_t vb2_ui_menu_prev(struct vb2_ui_context *ui)
	{
	int item;

	if (!DETACHABLE && ui->key == VB_BUTTON_VOL_UP_SHORT_PRESS)
	return VB2_REQUEST_UI_CONTINUE;

	item = ui->state->selected_item - 1;
	while (item >= 0 &&
	((1 << item) & ui->state->disabled_item_mask))
	item--;
	/* Only update if item is valid */
	if (item >= 0)
	ui->state->selected_item = item;

	return VB2_REQUEST_UI_CONTINUE;
	}

	vb2_error_t vb2_ui_menu_next(struct vb2_ui_context *ui)
	{
	int item;
	const struct vb2_menu *menu;

	if (!DETACHABLE && ui->key == VB_BUTTON_VOL_DOWN_SHORT_PRESS)
	return VB2_REQUEST_UI_CONTINUE;

	menu = get_menu(ui);
	item = ui->state->selected_item + 1;
	while (item < menu->num_items &&
	((1 << item) & ui->state->disabled_item_mask))
	item++;
	/* Only update if item is valid */
	if (item < menu->num_items)
	ui->state->selected_item = item;

	return VB2_REQUEST_UI_CONTINUE;
	}

	vb2_error_t vb2_ui_menu_select(struct vb2_ui_context *ui)
	{
	const struct vb2_menu *menu;
	const struct vb2_menu_item *menu_item;

	if (!DETACHABLE && ui->key == VB_BUTTON_POWER_SHORT_PRESS)
	return VB2_REQUEST_UI_CONTINUE;

	menu = get_menu(ui);
	if (menu->num_items == 0)
	return VB2_REQUEST_UI_CONTINUE;

	menu_item = &menu->items[ui->state->selected_item];

	if (menu_item->action) {
	VB2_DEBUG("Menu item <%s> run action\n", menu_item->text);
	return menu_item->action(ui);
	} else if (menu_item->target) {
	VB2_DEBUG("Menu item <%s> to target screen %#x\n",
	menu_item->text, menu_item->target);
	return vb2_ui_screen_change(ui, menu_item->target);
	}

	VB2_DEBUG("Menu item <%s> no action or target screen\n",
	menu_item->text);
	return VB2_REQUEST_UI_CONTINUE;
	}

	/*****************************************************************************/
	/* Screen navigation functions */

	vb2_error_t vb2_ui_screen_back(struct vb2_ui_context *ui)
	{
	struct vb2_screen_state *tmp;

	if (ui->state && ui->state->prev) {
	tmp = ui->state->prev;
	free(ui->state);
	ui->state = tmp;
	} else {
	VB2_DEBUG("ERROR: No previous screen; ignoring\n");
	}

	return VB2_REQUEST_UI_CONTINUE;
	}

	static vb2_error_t default_screen_init(struct vb2_ui_context *ui)
	{
	const struct vb2_menu *menu = get_menu(ui);
	ui->state->selected_item = 0;
	if (menu->num_items > 1 && menu->items[0].is_language_select)
	ui->state->selected_item = 1;
	return VB2_REQUEST_UI_CONTINUE;
	}

	vb2_error_t vb2_ui_screen_change(struct vb2_ui_context *ui, enum vb2_screen id)
	{
	const struct vb2_screen_info *new_screen_info;
	struct vb2_screen_state *cur_state;
	int state_exists = 0;

	new_screen_info = vb2_get_screen_info(id);
	if (new_screen_info == NULL) {
	VB2_DEBUG("ERROR: Screen entry %#x not found; ignoring\n", id);
	return VB2_REQUEST_UI_CONTINUE;
	}

	/* Check to see if the screen state already exists in our stack. */
	cur_state = ui->state;
	while (cur_state != NULL) {
	if (cur_state->screen->id == id) {
	state_exists = 1;
	break;
	}
	cur_state = cur_state->prev;
	}

	if (state_exists) {
	/* Pop until the requested screen is at the top of stack. */
	while (ui->state->screen->id != id) {
	cur_state = ui->state;
	ui->state = cur_state->prev;
	free(cur_state);
	}
	} else {
	/* Allocate the requested screen on top of the stack. */
	cur_state = malloc(sizeof(*ui->state));
	memset(cur_state, 0, sizeof(*ui->state));
	if (cur_state == NULL) {
	VB2_DEBUG("WARNING: malloc failed; ignoring\n");
	return VB2_REQUEST_UI_CONTINUE;
	}
	cur_state->prev = ui->state;
	cur_state->screen = new_screen_info;
	ui->state = cur_state;
	if (ui->state->screen->init)
	return ui->state->screen->init(ui);
	else
	return default_screen_init(ui);
	}

	return VB2_REQUEST_UI_CONTINUE;
	}

	/*****************************************************************************/
	/* Core UI loop */

	vb2_error_t ui_loop(struct vb2_context *ctx, enum vb2_screen root_screen_id,
	vb2_error_t (global_action)(struct vb2_ui_context ui))
	{
	struct vb2_ui_context ui;
	struct vb2_screen_state prev_state;
	int prev_disable_timer;
	enum vb2_ui_error prev_error_code;
	const struct vb2_menu *menu;
	const struct vb2_screen_info *root_info;
	uint32_t key_flags;
	vb2_error_t rv;

	memset(&ui, 0, sizeof(ui));
	ui.ctx = ctx;
	root_info = vb2_get_screen_info(root_screen_id);
	if (root_info == NULL)
	VB2_DIE("Root screen not found.\n");
	ui.locale_id = vb2_nv_get(ctx, VB2_NV_LOCALIZATION_INDEX);
	rv = vb2_ui_screen_change(&ui, root_screen_id);
	if (rv != VB2_REQUEST_UI_CONTINUE)
	return rv;
	memset(&prev_state, 0, sizeof(prev_state));
	prev_disable_timer = 0;
	prev_error_code = VB2_UI_ERROR_NONE;

	while (1) {
	/* Draw if there are state changes. */
	if (memcmp(&prev_state, ui.state, sizeof(*ui.state)) \|\|
	/* We want to redraw when timer is disabled. */
	prev_disable_timer != ui.disable_timer \|\|
	/* We want to redraw/beep on a transition. */
	prev_error_code != ui.error_code) {

	menu = get_menu(&ui);
	VB2_DEBUG("<%s> menu item <%s>\n",
	ui.state->screen->name,
	menu->num_items ?
	menu->items[ui.state->selected_item].text :
	"null");
	vb2ex_display_ui(ui.state->screen->id, ui.locale_id,
	ui.state->selected_item,
	ui.state->disabled_item_mask,
	ui.disable_timer,
	ui.error_code);
	if (ui.error_beep) {
	vb2ex_beep(250, 400);
	ui.error_beep = 0;
	}

	/* Update prev variables. */
	memcpy(&prev_state, ui.state, sizeof(*ui.state));
	prev_disable_timer = ui.disable_timer;
	prev_error_code = ui.error_code;
	}

	/* Grab new keyboard input. */
	ui.key = VbExKeyboardReadWithFlags(&key_flags);
	ui.key_trusted = !!(key_flags & VB_KEY_FLAG_TRUSTED_KEYBOARD);

	/* Check for shutdown request. */
	rv = check_shutdown_request(&ui);
	if (rv != VB2_REQUEST_UI_CONTINUE) {
	VB2_DEBUG("Shutdown requested!\n");
	return rv;
	}

	/* Check if we need to exit an error box. */
	rv = error_exit_action(&ui);
	if (rv != VB2_REQUEST_UI_CONTINUE)
	return rv;

	/* Run screen action. */
	if (ui.state->screen->action) {
	rv = ui.state->screen->action(&ui);
	if (rv != VB2_REQUEST_UI_CONTINUE)
	return rv;
	}

	/* Run menu navigation action. */
	rv = menu_navigation_action(&ui);
	if (rv != VB2_REQUEST_UI_CONTINUE)
	return rv;

	/* Run global action function if available. */
	if (global_action) {
	rv = global_action(&ui);
	if (rv != VB2_REQUEST_UI_CONTINUE)
	return rv;
	}

	/* Delay. */
	vb2ex_msleep(KEY_DELAY_MS);
	}

	return VB2_SUCCESS;
	}

	/*****************************************************************************/
	/* Developer mode */

	vb2_error_t vb2_developer_menu(struct vb2_context *ctx)
	{
	return ui_loop(ctx, VB2_SCREEN_DEVELOPER_MODE, developer_action);
	}

	vb2_error_t developer_action(struct vb2_ui_context *ui)
	{
	/* Developer mode keyboard shortcuts */
	if (ui->key == VB_KEY_CTRL('S'))
	return vb2_ui_screen_change(ui, VB2_SCREEN_DEVELOPER_TO_NORM);
	if (ui->key == VB_KEY_CTRL('U') \|\|
	(DETACHABLE && ui->key == VB_BUTTON_VOL_UP_LONG_PRESS))
	return vb2_ui_developer_mode_boot_external_action(ui);
	if (ui->key == VB_KEY_CTRL('D') \|\|
	(DETACHABLE && ui->key == VB_BUTTON_VOL_DOWN_LONG_PRESS))
	return vb2_ui_developer_mode_boot_internal_action(ui);

	/* TODO(b/144969088): Re-implement as debug info screen. */
	if (ui->key == '\t')
	VbDisplayDebugInfo(ui->ctx);

	return VB2_REQUEST_UI_CONTINUE;
	}

	/*****************************************************************************/
	/* Broken recovery */

	vb2_error_t vb2_broken_recovery_menu(struct vb2_context *ctx)
	{
	return ui_loop(ctx, VB2_SCREEN_RECOVERY_BROKEN, broken_recovery_action);
	}

	vb2_error_t broken_recovery_action(struct vb2_ui_context *ui)
	{
	/* TODO(b/144969088): Re-implement as debug info screen. */
	if (ui->key == '\t')
	VbDisplayDebugInfo(ui->ctx);

	return VB2_REQUEST_UI_CONTINUE;
	}

	/*****************************************************************************/
	/* Manual recovery */

	vb2_error_t vb2_manual_recovery_menu(struct vb2_context *ctx)
	{
	return ui_loop(ctx, VB2_SCREEN_RECOVERY_SELECT, manual_recovery_action);
	}

	vb2_error_t manual_recovery_action(struct vb2_ui_context *ui)
	{
	/* See if we have a recovery kernel available yet. */
	vb2_error_t rv = VbTryLoadKernel(ui->ctx, VB_DISK_FLAG_REMOVABLE);
	if (rv == VB2_SUCCESS)
	return rv;

	/* If disk validity state changed, switch to appropriate screen. */
	if (ui->recovery_rv != rv) {
	VB2_DEBUG("Recovery VbTryLoadKernel %#x --> %#x\n",
	ui->recovery_rv, rv);
	ui->recovery_rv = rv;
	return vb2_ui_screen_change(ui,
	rv == VB2_ERROR_LK_NO_DISK_FOUND ?
	VB2_SCREEN_RECOVERY_SELECT :
	VB2_SCREEN_RECOVERY_INVALID);
	}

	/* Manual recovery keyboard shortcuts */
	if (ui->key == VB_KEY_CTRL('D') \|\|
	(DETACHABLE && ui->key == VB_BUTTON_VOL_UP_DOWN_COMBO_PRESS))
	return vb2_ui_screen_change(ui, VB2_SCREEN_RECOVERY_TO_DEV);

	/* TODO(b/144969088): Re-implement as debug info screen. */
	if (ui->key == '\t')
	VbDisplayDebugInfo(ui->ctx);

	return VB2_REQUEST_UI_CONTINUE;
	}