Re: [Qemu-discuss] Qemu-system-sparc: What would I need to change to add functionality to save the nvram content between boots ?

[Peter Maydell]

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...

thanks
-- PMM