Re: [Qemu-devel] [PATCH 2/2] qxl: change rom so that 4096 < size < 8192

[Gerd Hoffmann]

On 12/13/12 12:36, Alon Levy wrote:
> This is a simpler solution to 869981, where migration breaks since qxl's
> rom bar size has changed. Instead of ignoring fields in QXLRom, which is what 
> has
> actually changed, we remove some of the modes, a mechanism already
> accounted for by the guest. To reach exactly two pages and not one, we
> remove two out of four orientations, the remaining are normal and right
> turn (chosen arbitrarily). Leaving only normal would result in a single
> page which would also break migration.
> 
> Added assertions to ensure changes in spice-protocol in the future
> causing increase or decrease of page size will result in failure at
> startup (could do this compile time also but not sure how).

The assertions are not in the patch.

>  #define QXL_MODE_EX(x_res, y_res)                 \
>      QXL_MODE_16_32(x_res, y_res, 0),              \
> -    QXL_MODE_16_32(y_res, x_res, 1),              \
> -    QXL_MODE_16_32(x_res, y_res, 2),              \
> -    QXL_MODE_16_32(y_res, x_res, 3)
> +    QXL_MODE_16_32(x_res, y_res, 1)

Why do you leave orientation = 1 in?  Just to keep the size above 4K?
Shouldn't we just hardcode the rom size to 8k instead?  Then assert that
everything fits into 8k?  Or even better add a compile time check?

While being at it it might be a good idea to move the mode table to a
fixed, large enougth offset (say 0x4096), so it doesn't move around
again in case we extend QXLRom one more time.

cheers,
  Gerd