Re: [Qemu-devel] [PULL 48/49] i386: populate floppy drive information in DSDT

[Roman Kagan]

On Mon, Feb 08, 2016 at 03:20:47PM -0500, John Snow wrote:
> On 02/08/2016 08:14 AM, Roman Kagan wrote:
> > On Fri, Feb 05, 2016 at 07:25:07PM +0100, Igor Mammedov wrote:
> >>> +    aml_append(fdi,
> >>> +        aml_int(cylinders - 1));  /* Maximum Cylinder Number */
> >> this puts uint64_t(-1) in AML i.e. cylinders == 0 and overflow happens here
> >>
> >> CCing Jon
> > 
> > I guess this is the effect of John's fdc rework.  I used to think zero
> > geometry was impossible at the time this patch was developed.
> > 
> > I wonder if it hasn't been fixed already by
> > 
> >   commit fd9bdbd3459e5b9d51534f0747049bc5b6145e07
> >   Author: John Snow <address@hidden>
> >   Date:   Wed Feb 3 11:28:55 2016 -0500
> > 
> >       fdc: fix detection under Linux
> 
> Yes, hopefully solved on my end. The geometry values for an empty disk
> are not well defined (they certainly don't have any *meaning*) so if you
> are populating tables based on an empty drive, I just hope you also have
> the mechanisms needed to update said tables when the media changes.

I don't.  At the time the patch was developed there basically were no
mechanisms to update the geometry at all (and this was what you patchset
addressed, in particular, wasn't it?) so I didn't care.

Now if it actually has to be fully dynamic it's gonna be more
involved...

> What do the guests use these values for? Are they fixed at boot?

Only Windows guests use it so it's hard to tell.  I can only claim that
if I stick bogus values into that ACPI object the guest fails to read
the floppy.

Roman.