Re: vnd geometry

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

On Tue, Apr 29, 2014 at 06:35:40PM +0200, J. Hannken-Illjes wrote:
> 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 ..)

That's what I meant by

"I am tempted to set plist's idea to sc_size"

But then "If I were to do that, I suspect I would break HASGEOM?"

?

Cheers,

Patrick