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Re: [Qemu-devel] OVMF, SeaBIOS & non-CSM based legacy boot

From: Jordan Justen
Subject: Re: [Qemu-devel] OVMF, SeaBIOS & non-CSM based legacy boot
Date: Thu, 24 Mar 2011 09:46:09 -0700

2011/3/24 Gleb Natapov <address@hidden>:
> 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.

What we really need is flash memory.  (See my 'hw/pc: Support system
flash memory' patch.)

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.

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. :)


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