[SeaBIOS] [PATCH] fix two issues with virtio-blk

[Kevin O'Connor]

On Sat, May 15, 2010 at 05:17:31PM +0200, Sebastian Herbszt wrote:
>Doing a read emulation
> in BIOS shouldn't be too bad, but a write emulation will need a "physical
> sector size" RMW buffer (no clue where the BIOS could steal those 4KB from).

SeaBIOS has a "malloc_low" function which obtains permanent memory in
the first 1Meg.  Currently, it grabs memory at the end of 640K (it
moves the ebda down if needed).  It's probably possible to use memory
in the c/d/e/f segments - though that's tricky because parts of that
area are likely to be read-only.

Right now SeaBIOS allocates a 2K buffer to support cdrom emulation
(this is different from what bochs bios does).  So, going to a 4K
buffer is probably reasonable.

-Kevin