[Xen-devel] Re: [patch 02/21] Xen-paravirt: Handle a zero-sized VT console

[Gerd Hoffmann <kraxel@xxxxxxx>]

Jeremy Fitzhardinge wrote:
> If we're running under Xen, then there's no VT console.  This results
> in vc->vc_screenbuf_size == 0, which causes alloc_bootmem to panic.
> Don't bother allocating a vc_screenbuf if its going to be 0 sized.

NAK.

The *real* problem is that the real-mode boot code never ever runs, thus
SCREEN_INFO is not initialized (all zeros), and vgacon doesn't catch
that case.  Instead it thinks it runs on a EGA card with 0 lines and 0
columns.

So better fix vgacon to catch this and switch to the 80x25 dummy console
instead, patch attached.

cheers,

  Gerd

---
 drivers/video/console/vgacon.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: paravirt-2.6.20-hg749/drivers/video/console/vgacon.c
===================================================================
--- paravirt-2.6.20-hg749.orig/drivers/video/console/vgacon.c
+++ paravirt-2.6.20-hg749/drivers/video/console/vgacon.c
@@ -372,7 +372,8 @@ static const char *vgacon_startup(void)
        }
 
        /* VGA16 modes are not handled by VGACON */
-       if ((ORIG_VIDEO_MODE == 0x0D) ||        /* 320x200/4 */
+       if ((ORIG_VIDEO_MODE == 0x00) ||        /* SCREEN_INFO not initialized 
*/
+           (ORIG_VIDEO_MODE == 0x0D) ||        /* 320x200/4 */
            (ORIG_VIDEO_MODE == 0x0E) ||        /* 640x200/4 */
            (ORIG_VIDEO_MODE == 0x10) ||        /* 640x350/4 */
            (ORIG_VIDEO_MODE == 0x12) ||        /* 640x480/4 */

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