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Re: [Qemu-discuss] Qemu-system-sparc: What would I need to change to add

From: Jakob Bohm
Subject: Re: [Qemu-discuss] Qemu-system-sparc: What would I need to change to add functionality to save the nvram content between boots ?
Date: Mon, 14 Sep 2015 16:44:24 +0200
User-agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0

On 14/09/2015 11:33, Peter Maydell wrote:
On 14 September 2015 at 00:25, Programmingkid <address@hidden> wrote:
On Sep 13, 2015, at 7:20 PM, Bodo Eggert wrote:

On Sun, 13 Sep 2015, Programmingkid wrote:
On Sep 13, 2015, at 5:50 PM, Bodo Eggert wrote:
On Sun, 13 Sep 2015, Mark Cave-Ayland wrote:
On 11/09/15 19:01, Programmingkid wrote:
Mark, do you think it is possible for a QEMU command line option to
actually load the
saved OpenBIOS settings from a file and restore them into memory? I'm
thinking something
along the lines of -prom-memory <file name>.
From memory the reason this hasn't been done is because the NVRAM
interface is used across multiple architectures and there hasn't been a
solution devised that would work well enough for all of them. Then again
as the BIOSs involved have continued to develop, it may be now that some
of the issues can now be solved so it never hurts to ask on the -devel list.
I'm wondering, why wouldn't it be enough to memmap a nvram file instead of
mallocing (or whatever) the memory area?
What advantage does mmap() have over malloc()? I think malloc() is a lot more
familiar to use than mmap().
The advantage is that it's file-backed (optionally, but intended here).
Everything you write into that memory area will be automatically
saved and restored just like a nvram should be. At least, that's what the
documentation promises, I never used it myself, therefore I ask.
You make mmap() sound good. Maybe we should use it.
Rather than reinventing the wheel I suggest looking at how QEMU
already supports file-backed ROMs for other platforms...
Note that this is about *writable* persistent memory,
such as the non-time battery backed registers in a PC
clock or the thing that stores EFI BIOS variables such
as those holding Linux crash dumps.


Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark.  Direct +45 31 13 16 10
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