On 02/09/2016 10:52 AM, Roman Kagan wrote:
> 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 <js...@redhat.com>
>>> 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.
>
That's not true.
You could swap different 1.44MB-class diskettes for other geometries,
check this out:
static const FDFormat fd_formats[] = {
/* First entry is default format */
/* 1.44 MB 3"1/2 floppy disks */
{ FDRIVE_DRV_144, 18, 80, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 20, 80, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 21, 80, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 21, 82, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 21, 83, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 22, 80, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 23, 80, 1, FDRIVE_RATE_500K, },
{ FDRIVE_DRV_144, 24, 80, 1, FDRIVE_RATE_500K, },
...
You absolutely could get different sector and track counts before my
patchset.
> 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.
>
--
—js
