[Qemu-devel] Re: [PATCH] update bochs vbe interface

[Juan Quintela]

Gerd Hoffmann <address@hidden> wrote:
> On 03/24/10 18:04, Juan Quintela wrote:
>> Gerd Hoffmann<address@hidden>  wrote:
>>> The bochs vbe interface got a new register a while back, which specifies
>>> the linear framebuffer size in 64k units.  This patch adds support for
>>> the new register to qemu.  With this patch applied vgabios 0.6c works
>>> with qemu.
>>>
>>> Signed-off-by: Gerd Hoffmann<address@hidden>
>>
>> It breaks migration.
>>
>> vga.c:2218:        VMSTATE_UINT16_ARRAY(vbe_regs, VGACommonState, 
>> VBE_DISPI_INDEX_NB),
>
>> 2218 is the interesting line.  Can we freeze this patch until the
>> subsections stuff is done?
>
> Yea, I see.  Well, the new register doesn't carry any state, it is
> read-only information for the guest.  So the easy way out is to simply
> not save it as we don't have to.

Thinking a bit more about it.

Humm, I think it means.  Can you migrate from a "new" vga to an old one,
and maintain it working?

-    s->vbe_regs[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID0;
+    s->vbe_regs[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID5;
+    s->vbe_regs[VBE_DISPI_INDEX_VIDEO_MEMORY_64K] = s->vram_size / (64 * 1024);

After migration, vbe_regs[VBE_DISPI_INDEX_ID] would have the value
VBE_DISPI_ID5, but vbe_regs[VBE_DISPI_INDEX_VIDEO_MEMORY_64K] will have
any random value, no?

>
> cheers,
>   Gerd