kern/term: Accept ESC, F4 and holding SHIFT as user interrupt keys

On some devices the ESC key is the hotkey to enter the BIOS/EFI setup
screen, making it really hard to time pressing it right. Besides that
ESC is also pretty hard to discover for a user who does not know it
will unhide the menu.

This commit makes F4, which was chosen because is not used as a hotkey
to enter the BIOS setup by any vendor, also interrupt sleeps / stop the
menu countdown.

This solves the ESC gets into the BIOS setup and also somewhat solves
the discoverability issue, but leaves the timing issue unresolved.

This commit fixes the timing issue by also adding support for keeping
SHIFT pressed during boot to stop the menu countdown. This matches
what Ubuntu is doing, which should also help with discoverability.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

docs/grub.texi

@@ -1330,12 +1330,12 @@ menu and then wait for the timeout set by @samp{GRUB_TIMEOUT} to expire
 before booting the default entry.  Pressing a key interrupts the timeout.
 
 If this option is set to @samp{countdown} or @samp{hidden}, then, before
-displaying the menu, GRUB will wait for the timeout set by
-@samp{GRUB_TIMEOUT} to expire.  If @key{ESC} is pressed during that time, it
-will display the menu and wait for input.  If a hotkey associated with a
-menu entry is pressed, it will boot the associated menu entry immediately.
-If the timeout expires before either of these happens, it will boot the
-default entry.  In the @samp{countdown} case, it will show a one-line
+displaying the menu, GRUB will wait for the timeout set by @samp{GRUB_TIMEOUT}
+to expire.  If @key{ESC} or @key{F4} are pressed, or @key{SHIFT} is held down
+during that time, it will display the menu and wait for input.  If a hotkey
+associated with a menu entry is pressed, it will boot the associated menu entry
+immediately. If the timeout expires before either of these happens, it will
+boot the default entry.  In the @samp{countdown} case, it will show a one-line
 indication of the remaining time.
 
 @item GRUB_DEFAULT_BUTTON
@@ -1559,16 +1559,16 @@ configurations, but have better replacements:
 
 @table @samp
 @item GRUB_HIDDEN_TIMEOUT
-Wait this many seconds before displaying the menu.  If @key{ESC} is pressed
-during that time, display the menu and wait for input according to
-@samp{GRUB_TIMEOUT}.  If a hotkey associated with a menu entry is pressed,
-boot the associated menu entry immediately.  If the timeout expires before
-either of these happens, display the menu for the number of seconds
-specified in @samp{GRUB_TIMEOUT} before booting the default entry.
+Wait this many seconds before displaying the menu.  If @key{ESC} or @key{F4} are
+pressed, or @key{SHIFT} is held down during that time, display the menu and wait
+for input according to @samp{GRUB_TIMEOUT}.  If a hotkey associated with a menu
+entry is pressed, boot the associated menu entry immediately.  If the timeout
+expires before either of these happens, display the menu for the number of
+seconds specified in @samp{GRUB_TIMEOUT} before booting the default entry.
 
 If you set @samp{GRUB_HIDDEN_TIMEOUT}, you should also set
 @samp{GRUB_TIMEOUT=0} so that the menu is not displayed at all unless
-@key{ESC} is pressed.
+@key{ESC} or @key{F4} are pressed, or @key{SHIFT} is held down.
 
 This option is unset by default, and is deprecated in favour of the less
 confusing @samp{GRUB_TIMEOUT_STYLE=countdown} or
@@ -5162,9 +5162,10 @@ Alias for @code{hashsum --hash sha512 arg @dots{}}. See command @command{hashsum
 
 @deffn Command sleep [@option{--verbose}] [@option{--interruptible}] count
 Sleep for @var{count} seconds. If option @option{--interruptible} is given,
-allow @key{ESC} to interrupt sleep. With @option{--verbose} show countdown
-of remaining seconds. Exit code is set to 0 if timeout expired and to 1
-if timeout was interrupted by @key{ESC}.
+allow pressing @key{ESC}, @key{F4} or holding down @key{SHIFT} to interrupt
+sleep.  With @option{--verbose} show countdown of remaining seconds. Exit code
+is set to 0 if timeout expired and to 1 if timeout was interrupted using any
+of the mentioned keys.
 @end deffn
 
 

grub-core/commands/sleep.c

@@ -55,7 +55,7 @@ grub_interruptible_millisleep (grub_uint32_t ms)
   start = grub_get_time_ms ();
 
   while (grub_get_time_ms () - start < ms)
-    if (grub_getkey_noblock () == GRUB_TERM_ESC)
+    if (grub_key_is_interrupt (grub_getkey_noblock ()))
       return 1;
 
   return 0;

grub-core/kern/term.c

@@ -138,6 +138,27 @@ grub_getkeystatus (void)
   return status;
 }
 
+int
+grub_key_is_interrupt (int key)
+{
+  /*
+   * ESC sometimes is the BIOS setup hotkey and may be hard to discover, also
+   * check F4, which was chosen because is not used as a hotkey to enter the
+   * BIOS setup by any vendor.
+   */
+  if (key == GRUB_TERM_ESC || key == GRUB_TERM_KEY_F4)
+    return 1;
+
+  /*
+   * Pressing keys at the right time during boot is hard to time, also allow
+   * interrupting sleeps / the menu countdown by keeping shift pressed.
+   */
+  if (grub_getkeystatus() & (GRUB_TERM_STATUS_LSHIFT | GRUB_TERM_STATUS_RSHIFT))
+    return 1;
+
+  return 0;
+}
+
 void
 grub_refresh (void)
 {

grub-core/normal/menu.c

@@ -623,7 +623,7 @@ run_menu (grub_menu_t menu, int nested, int *auto_boot)
 	      if (entry >= 0)
 		break;
 	    }
-	  if (key == GRUB_TERM_ESC)
+	  if (grub_key_is_interrupt (key))
 	    {
 	      timeout = -1;
 	      break;

include/grub/term.h

@@ -330,6 +330,7 @@ void grub_putcode (grub_uint32_t code, struct grub_term_output *term);
 int EXPORT_FUNC(grub_getkey) (void);
 int EXPORT_FUNC(grub_getkey_noblock) (void);
 int EXPORT_FUNC(grub_getkeystatus) (void);
+int EXPORT_FUNC(grub_key_is_interrupt) (int key);
 void grub_cls (void);
 void EXPORT_FUNC(grub_refresh) (void);
 void grub_puts_terminal (const char *str, struct grub_term_output *term);