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SubjectRe: Disk geometry from /sys
On Wed, Apr 23, 2008 at 12:44 AM, Mark Lord <lkml@rtr.ca> wrote:
> > On Fri, Apr 18, 2008 at 3:22 PM, Mark Lord <lkml@rtr.ca> wrote:
> >
> > > That can sound a bit misleading. The complete story, for ATA/SATA
> drives,
> > > is that the disk has two geometries: an internal physical one, with a
> > > fixed number of heads and cylinders, but variable sectors/track
> > > (which normally varies by cylinder zone).
> > >
> > > Software *never* sees or knows about that geometry, so ignore it.
> > >
> > > The second geometry, is the one that the drive reports to software
> > > as its "native" geometry. This is what you see from "hdparm -I"
> > > and friends, and this geometry is what has to be used by software
> > > when using cylinder/head/sector (CHS) addressing for I/O operations.
> > > The hardware interface has a limit of 4-bits for the head value,
> > > so the maximum number of heads can never be more than 16.
> > >
> > > Nobody uses CHS addressing for I/O operations, at least not on
> > > any hardware newer than at least ten years old, so this geometry
> > > is also unimportant for most uses.
> > >
> > >
> >
> > Is it because IDE drives support several IO operation modes ?
> >
> ..
>
> The earliest IDE drives for Compaq used only CHS sector addressing mode.
>
> Within four years, though, all new drives had support for the more sensible
> linear block addressing (LBA) mode, as well.
>

My last question I promise ;)

If I'd like to take a look in the kernel code to see where the kernel
translates an offset
provided by sys_read into a LBA or CHS address, where should I go ?
drivers/block ?

Thanks !
--
Francis


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