On Tue, Mar 08, 2011 at 09:13:38AM -0800, Jordan Justen wrote:
> 2011/3/8 Gleb Natapov <g...@redhat.com>:
> > On Tue, Mar 08, 2011 at 07:18:09AM +0000, Stefan Hajnoczi wrote:
> >> > Regarding the non-volatile variables issue, I have been trying to
> >> > develop a proposal for addressing this with a change to QEMU's
> >> > hardware support of bios.bin. But, I don't have the suggestion (or
> >> > implementation) ready at this time.
> >>
> >> Sounds like something to keep discussing with the QEMU and SeaBIOS
> >> communities. Gleb Natapov and Kevin O'Connor have done a lot of the
> >> recent BIOS and firmware interface work. I think persistent CMOS has
> >> come up several times and might be similar to non-volatile UEFI
> >> storage.
> >>
> > What kind of information OVMF stores on a persistent storage?
>
> Non-volatile variables are a general system wide environment variable
> storage facility, but one key thing to store (for instance) is the
> path to the boot image.
>
> > CMOS
> > memory is less them 512 byte IIRC and this may not be enough. What OVMF
> > uses on real HW for non-volatile storage?
>
> Regarding CMOS, I think qemu exposes 128 bytes of non persistent CMOS
> RAM. Many current chipsets provide another bank of 128 bytes, meaning
> a total of 256 bytes (minus the RTC registers).
>
> Regarding UEFI non-volatile variables on real HW:
> Most systems today have at least 1MB of flash storage located just
> below 4GB. The entire contents can be modified, which is how firmware
> updates happen.
>
How this flash storage is programmed? May be we can emulate something
similar.
> For a UEFI based system, the non-volatile variables generally occupy
> 8KB~64KB of the flash depending on flash space availability.
>
> -Jordan
--
Gleb.
