linux-kernel - Re: Disk geometry from /sys

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Message-ID: <38b2ab8a0804230002x4b626fa6p89fe940e8e0ff374@mail.gmail.com>
Date:	Wed, 23 Apr 2008 09:02:33 +0200
From:	"Francis Moreau" <francis.moro@...il.com>
To:	"Mark Lord" <lkml@....ca>
Cc:	"Seewer Philippe" <philippe.seewer@....ch>,
	linux-kernel@...r.kernel.org
Subject: Re: Disk geometry from /sys

On Wed, Apr 23, 2008 at 12:44 AM, Mark Lord <lkml@....ca> wrote:
> > On Fri, Apr 18, 2008 at 3:22 PM, Mark Lord <lkml@....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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