[PATCH] Improve handling of "keep" in gfxpayload

[Colin Watson <cjwatson@ubuntu.com>]

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If the user set "keep" in gfxpayload, as I understand it, that indicates
that they want the graphical mode set by GRUB to persist through to the
kernel. In order for this to actually work with Linux, we need to set up
the vid_mode boot parameter to indicate that it should keep the current
video mode, otherwise it'll just reset the mode to text at boot and
nothing much is gained. This patch fixes that.

Note that I'm explicitly not enabling GRUB_ASSUME_LINUX_HAS_FB_SUPPORT
in the Ubuntu grub2 package. I can understand why support for it was
added, and I'd be willing to assume that the Ubuntu kernel has the
necessary support, but I'm not willing to assume that every Linux kernel
booted by the Ubuntu grub2 build has the necessary support; that seems
one assumption too far for me. As such I'm interested in making this
work properly with run-time configuration as well as build-time
configuration.

This doesn't quite work perfectly yet. It's better than before - I've
tested this, and if everything works properly then the result is a
smooth zero-flicker transition, which is wonderful. However, if
something goes wrong before the kernel starts a framebuffer then it has
no way to display any text at all, and it doesn't seem to start one
until relatively late for me. It may be that the next step here is to
try to explicitly tell the kernel to set the correct VESA mode rather
than using 0x0F04, but I thought I'd send this patch anyway in the
meantime ...

2009-08-10  Colin Watson  <cjwatson@ubuntu.com>

        * include/grub/i386/linux.h (GRUB_LINUX_VID_MODE_CURRENT): New
        macro.
        * loader/i386/linux.c (grub_linux_boot): If gfxpayload starts
        with "keep", or if GRUB_ASSUME_LINUX_HAS_FB_SUPPORT is defined,
        then set the vid_mode boot parameter to
        GRUB_LINUX_VID_MODE_CURRENT.

Thanks,

-- 
Colin Watson                                       [cjwatson@ubuntu.com]

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diff -Nur -x '*.orig' -x '*~' grub2-1.96+20090725/include/grub/i386/linux.h grub2-1.96+20090725.new/include/grub/i386/linux.h
--- grub2-1.96+20090725/include/grub/i386/linux.h	2009-07-06 03:10:57.000000000 +0100
+++ grub2-1.96+20090725.new/include/grub/i386/linux.h	2009-08-08 19:45:10.000000000 +0100
@@ -39,6 +39,7 @@
 #define GRUB_LINUX_VID_MODE_NORMAL	0xFFFF
 #define GRUB_LINUX_VID_MODE_EXTENDED	0xFFFE
 #define GRUB_LINUX_VID_MODE_ASK		0xFFFD
+#define GRUB_LINUX_VID_MODE_CURRENT	0x0F04
 #define GRUB_LINUX_VID_MODE_VESA_START	0x0300
 
 #define GRUB_LINUX_SETUP_MOVE_SIZE	0x9100
diff -Nur -x '*.orig' -x '*~' grub2-1.96+20090725/loader/i386/linux.c grub2-1.96+20090725.new/loader/i386/linux.c
--- grub2-1.96+20090725/loader/i386/linux.c	2009-08-08 19:31:00.000000000 +0100
+++ grub2-1.96+20090725.new/loader/i386/linux.c	2009-08-08 19:45:09.000000000 +0100
@@ -446,6 +446,7 @@
   int e820_num;
   grub_err_t err = 0;
   char *modevar, *tmp;
+  int keep_mode = 0;
 
   params = real_mode_mem;
 
@@ -460,11 +461,19 @@
       if (! tmp)
 	return grub_errno;
       grub_sprintf (tmp, "%s;" DEFAULT_VIDEO_MODE, modevar);
+#ifndef GRUB_ASSUME_LINUX_HAS_FB_SUPPORT
+      if (grub_memcmp (modevar, "keep", sizeof ("keep")) == 0
+	  || grub_memcmp (modevar, "keep,", sizeof ("keep,") - 1) == 0
+	  || grub_memcmp (modevar, "keep;", sizeof ("keep;") - 1) == 0)
+	keep_mode = 1;
+#endif
       err = grub_video_set_mode (tmp, 0);
       grub_free (tmp);
     }
-#ifndef GRUB_ASSUME_LINUX_HAS_FB_SUPPORT
   else
+#ifdef GRUB_ASSUME_LINUX_HAS_FB_SUPPORT
+    keep_mode = 1;
+#else
     err = grub_video_set_mode (DEFAULT_VIDEO_MODE, 0);
 #endif
 
@@ -474,6 +483,8 @@
       grub_printf ("Booting however\n");
       grub_errno = GRUB_ERR_NONE;
     }
+  else if (keep_mode)
+    params->vid_mode = GRUB_LINUX_VID_MODE_CURRENT;
 
   if (! grub_linux_setup_video (params))
     params->have_vga = GRUB_VIDEO_TYPE_VLFB;