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Date: Wed, 22 Sep 2010 21:43:29 +0200
From: Mathias Krause <mathias.krause@secunet.com>
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Subject: Re: [Qemu-devel] [PATCH] CMOS file support
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>

On 17.09.2010 15:27, Anthony Liguori wrote:
> On 09/17/2010 01:50 AM, Mathias Krause wrote:
>> Am 16.09.2010 19:20 schrieb Anthony Liguori:
>>   
>>> Instead of using FILE, I'd suggest using a BlockDriver to read and write
>>> the data.
>>>      
>> I'll fix that as soon as I figured how to use this interface.
>>
>>   
>>> I think it would be very nice to add write support too so that writes to
>>> CMOS were persisted across boots.
>>>      
>> Indeed. Also I would like to have a command line interface like '-cmos
>> cmos.bin' instead of the ugly '-global mc146818rtc.file=cmos.bin'. But
>> I'm not aware how to create such an alias. Any pointers?
>>    
> 
> Unfortunately, it's a little complicated although it should get better
> in the future.   The right way to do this today would be:
> 
>   -drive file=cmos.bin,if=none,id=nvram -global mc146818rtc.drive=nvram
> 
> The use of -drive is historic.  We'll have a better option in the future
> that will look something like:
> 
>  -blockdev file=cmos.bin,id=nvram -global mc146818rtc.drive=nvram

Well, I guess "better" lies in the eye of the beholder, then ;)


> But in either case, I'd suggest adding an -nvram option that was:
> 
>  -nvram <filename>
> 
> Which would do:
> 
>   drive_add(optarg, "if=none,id=nvram");
> 
> And then in the RTC code, default drive to nvram.

I managed to add the nvram option but how do I get a reference to the
drive back in the RTC code? Would I just loop with drive_get(IF_NONE, 0,
i) until the id of the returned drive is "nvram"? Doesn't sound right
but I've found no better solution due to the lack of an
drive_get_by_id() function.

> It gets a little tough to handle the case of in memory CMOS.

I don't quite get your point here. The content of the drive is copied in
the RTC init routine into a private char array. How could the type of
the drive may be a problem here?


Regards,

Mathias