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Date: Wed, 17 Nov 2010 14:28:21 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH] spice: add qxl device
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org

On 11/16/10 18:43, Michael S. Tsirkin wrote:
> On Tue, Nov 02, 2010 at 02:34:58PM +0100, Gerd Hoffmann wrote:
>> +        if (ram_size<  32 * 1024 * 1024)
>> +            ram_size = 32 * 1024 * 1024;
>> +        vga_common_init(vga, ram_size);
>> +        vga_init(vga);
>> +        register_ioport_write(0x3c0, 16, 1, qxl_vga_ioport_write, vga);
>> +        register_ioport_write(0x3b4,  2, 1, qxl_vga_ioport_write, vga);
>> +        register_ioport_write(0x3d4,  2, 1, qxl_vga_ioport_write, vga);
>> +        register_ioport_write(0x3ba,  1, 1, qxl_vga_ioport_write, vga);
>> +        register_ioport_write(0x3da,  1, 1, qxl_vga_ioport_write, vga);
>> +
>> +        vga->ds = graphic_console_init(qxl_hw_update, qxl_hw_invalidate,
>> +                                       qxl_hw_screen_dump, qxl_hw_text_update, qxl);
>> +        qxl->ssd.ds = vga->ds;
>> +        qxl->ssd.bufsize = (16 * 1024 * 1024);
>> +        qxl->ssd.buf = qemu_malloc(qxl->ssd.bufsize);
>> +
>> +        qxl0 = qxl;
>
> What happens when this device is then removed?

Better don't try ...

The primary vga can't be hot-unplugged in qemu.  Not only because the 
qxl0 pointer would point into nowhere in this case, but also because you 
can't unregister the graphic console.  Also having non-pci ressources 
(legacy vga I/O ports) is a problem.

>> +        pci_config_set_class(config, PCI_CLASS_DISPLAY_VGA);
>> +    } else {
>> +        pci_config_set_class(config, PCI_CLASS_DISPLAY_OTHER);
>
> So 1st device has device id different from the rest?

Yes.

> Why?

Because the first one actually *is* different. It is the only one which 
is vga compatible.  It serves as primary display.  You'll see the boot 
messages there.

>> +    device_id++;
>
> what happens when this wraps around?
> Since it's an int probably undefined behaviour ...

I doubt you'll see it wrap in any real world scenario.  Even with one
hotplug + unplug cycle per second you'll need a bunch of years to see it 
wrap.  Beside that at least in windows the device can't be unplugged in 
the first place, windows will veto the unplug request.

cheers,
   Gerd