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

[Anthony Liguori]

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

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.

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

Regards,

Anthony Liguori

>    
> > > +static long get_file_size(FILE *f)
> > > +{
> > > +    long where, size;
> > > +
> > > +    /* XXX: on Unix systems, using fstat() probably makes more sense */
> > > +
> > > +    where = ftell(f);
> > > +    fseek(f, 0, SEEK_END);
> > > +    size = ftell(f);
> > > +    fseek(f, where, SEEK_SET);
> > > +
> > > +    return size;
> > > +}
> > >
> > >        
> > BlockDrivers have a getlength() functions.
> >      
> Would reduce the size of the patch which is always a good thing (tm).
>
>
> Mathias
>