Re: vnd geometry

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

On 29 Apr 2014, at 18:23, Patrick Welche <prlw1%cam.ac.uk@localhost> wrote:

> On Tue, Apr 29, 2014 at 04:44:52PM +0100, Patrick Welche wrote:
>> On Tue, Apr 29, 2014 at 04:08:02PM +0200, J. Hannken-Illjes wrote:
>>> On 29 Apr 2014, at 15:19, Patrick Welche <prlw1%cam.ac.uk@localhost> wrote:
>>> 
>>> <snip>
>>>> 
>>>> One oddity while perusing the code is:
>>>> 
>>>>       /*
>>>>        * Use pseudo-geometry specified.  If none was provided,
>>>>        * use "standard" Adaptec fictitious geometry.
>>>>        */
>>>>       if (vio->vnd_flags & VNDIOF_HASGEOM) {
>>>> 
>>>>           memcpy(&vnd->sc_geom, &vio->vnd_geom,
>>>>               sizeof(vio->vnd_geom));
>>>> 
>>>> How can VNDIOF_HASGEOM ever be set?
>>> 
>>> With <geomspec> from vnconfig(8)?
>> 
>> Ah thanks - I just used fxr.watson.org...
>> 
>> It seems that disklabel and plist agree at least for sizes which are
>> whole numbers of megabytes, e.g.,
>> 
>> bytes:
>> disklabel        plist backing_file
>> 10485760     10485760     10485760  =  A00000 
>> 136314880    136314880    136314880  = 8200000
>> 12761600     12582912     12761760 (this row in hex below)
>>   C2BA00       C00000       C2BAA0
> 
> plist gets its idea of size by multiplying nsectors*ntracks*ncylinders.
> disklabel gets its idea of size by rounding down the backing file size
> to the nearest number of disk blocks.
> 
> I am tempted to set plist's idea to sc_size as per the disklabel.
> If I were to do that, I suspect I would break HASGEOM?
> 
> OK to change struct vndgeom to add a vng_size member and set it as
> appropriate according to HASGEOM? But then VNDIOC{SET,CLR}50 would
> break?
> 
> Thoughts?

In vnd_set_geometry():

- dg->dg_secperunit = (int64_t)vnd->sc_geom.vng_nsectors *
-            vnd->sc_geom.vng_ntracks * vnd->sc_geom.vng_ncylinders;

+ dg->dg_secperunit = vnd->sc_size;

(completely untested of course ..)

--
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig 
(Germany)