On Thu, Mar 24, 2011 at 09:46:09AM -0700, Jordan Justen wrote:
> 2011/3/24 Gleb Natapov <g...@redhat.com>:
> > On Wed, Mar 23, 2011 at 03:32:41PM -0700, Jordan Justen wrote:
> >> By the way, today OVMF attempts to store NV-Var data in a file on the
> >> disk, but this cannot support variables at runtime. (This is why I
> >> sent in the patch for using -pflash on x86/x86-64.)
> >>
> > And this file is stored always at the same location? If it is then then
> > problem is solved! But what do you mean by "this cannot support
> > variables at runtime"?
>
> The variables can be set while the OS is running, and the OS has
> exclusive control over the disk at that time. Today in OVMF we set
> variables into memory during this time, and hope that memory it still
> around after a reset. This does not provide realistic non-volatile
> UEFI variable support.
KVM preserve memory during reset, but we better not rely on that.
>
> What we really need is flash memory. (See my 'hw/pc: Support system
> flash memory' patch.)
Storing boot file only on flash memory will require to distribute the
flash image along with disk image.
>
> But, there is nothing stopping us from also storing the variables on
> the disk (during the firmware boot), and also using them as a backup.
>
This will still require at least one reboot for variables to be saved in
a filesystem, but this is better then nothing.
> Additionally, we can add yet another backup system of looking for
> known os-loader executable paths. This would be needed if a disk
> image were ever to be transferred from a real machine to a VM image.
> But, this would require firmware updates as new UEFI OS loader install
> paths are added. Also, let's hope no OS decides to generate a random
> path for the OS loader. :)
>
Firmware updates in a VM is very easy, so not a big deal.
--
Gleb.
