Re: [Qemu-devel] [PATCH] CMOS file support

[Markus Armbruster <armbru@redhat.com>]

Anthony Liguori <anthony@codemonkey.ws> writes:

> On 09/16/2010 08:58 AM, Mathias Krause wrote:
>> In contrast to the BIOS and Option ROMs the CMOS content cannot be
>> predefined by the user. Also the amount of useable CMOS ARM is pretty
>> limited, even though the amount of CMOS bytes emulated by qemu is
>> already twice as much as of the original MC146818. Nevertheless those
>> limitations are pretty annoying when testing different BIOS replacement
>> implementations like coreboot in combination with FILO that use CMOS
>> values above the basic RTC range for its own purpose to, e.g., control
>> the boot device order using a string containing the boot devices to
>> probe.
>>
>> This patch adds support to specify a file to read the initial CMOS
>> content from. It also increases the CMOS size to 256 bytes and
>> implements access to the extended memory range via I/O ports 0x72 and
>> 0x73.
>>
>> Use it like: `qemu -global mc146818rtc.file=cmos.bin ...' where cmos.bin
>> is a binary file, sized 256 bytes containing the CMOS RAM.
>>
>> Signed-off-by: Mathias Krause<mathias.krause@secunet.com>
>>    
>
> Instead of using FILE, I'd suggest using a BlockDriver to read and
> write the data.
>
> I think it would be very nice to add write support too so that writes
> to CMOS were persisted across boots.

Persisting CMOS makes it state instead of configuration.  Use of block
layer (treat it like a drive) makes more sense then.