Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive

[Laszlo Ersek]

On 11/27/13 18:22, Markus Armbruster wrote:

> Perhaps the proper way to back partially writable flash contents isn't
> splitting it into two devices, but backing a single device with a COW.
> The backing file has initial contents (say BIOS image), the delta may
> have additional contents (say non-volatile configuration), and picks up
> whatever the device model permits to be written to the flash.

Kevin brought this up before. The problem is that this prevents you from
upgrading the read-only part in O(1).

(Unless of course you're willing to make the backing file raw *and* to
poke directly in it when you upgrade the bios binary part. Theoretically
you could do this, because the divide between the varstore and the
binary part at 128KB falls at a qcow2 block boundary (supposing a 64K
qcow2 block size), but in practice this is a horrible idea :))

Let's not veer off into architecting a new star destroyer. I think I
have plenty ammo from your great notes thus far that I can hack up a v2
with :)

Thanks
Laszlo