linux-kernel - What to do about the 2TB limit on HDIO

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Date:	Tue, 25 Mar 2008 00:02:10 -0400
From:	Mark Lord <lkml@....ca>
To:	Jens Axboe <axboe@...nel.dk>, Jeff Garzik <jgarzik@...ox.com>,
	Tejun Heo <htejun@...il.com>, Greg KH <gregkh@...e.de>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: What to do about the 2TB limit on HDIO_GETGEO ?

(resending .. forgot to copy the lists originally)

We have a problem coming down the pipeline.

Practically all utilities that care about it,
use ioctl(fd, HDIO_GETGEO) to determine the starting
sector offset of a hard disk partition.

SCSI, libata, IDE, USB, Firewire.. you name it.

The return value uses "unsigned long",
which on a 32-bit system limits drive offsets to 2TB.

There will be single drives exceeding this limit within
the next 12 months or less, and we already have RAID arrays
that exceed 2TB.

So.. what's the replacement for HDIO_GETGEO on 32-bits ?

One candidate might seem to be the existing /sys/block/dev/partition/start
which I expect is already 64-bit friendly.

But this requires about 150 lines of somewhat complex C code to access,
using only the dev_t (from stat(2) on a file) as a starting point,
or less if one relies upon the udev device name matching the sysfs device name.

Is it time now for HDIO_GETGEO64 to make an appearance?
Similar to how the existing BLKGETSIZE64 is supplanting BLKGETSIZE ?

??
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