linux-kernel - Re: [PATCH] libata: Don't trust current capacity values in identify words 57-58

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Message-ID: <4999F032.6060107@rtr.ca>
Date:	Mon, 16 Feb 2009 18:01:06 -0500
From:	Mark Lord <liml@....ca>
To:	Robert Hancock <hancockrwd@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	ide <linux-ide@...r.kernel.org>, Jeff Garzik <jeff@...zik.org>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Hanno Böck <hanno@...eck.de>
Subject: Re: [PATCH] libata: Don't trust current capacity values in identify
 words 57-58

Robert Hancock wrote:
> Hanno Böck reported a problem where an old Conner CP30254 240MB hard drive
> was reported as 1.1TB in capacity by libata:
> 
> http://lkml.org/lkml/2009/2/13/134
> 
> This was caused by libata trusting the drive's reported current capacity in 
> sectors in identify words 57 and 58 if the drive does not support LBA and the
> current CHS translation values appear valid. Unfortunately it seems older
> ATA specs were vague about what this field should contain and a number of drives
> used values with wrong byte order or that were totally bogus. There's no
> unique information that it conveys and so we can just calculate the number
> of sectors from the reported current CHS values.
> 
> Signed-off-by: Robert Hancock <hancockrwd@...il.com>
..
>  	} else {
>  		if (ata_id_current_chs_valid(id))
> -			return ata_id_u32(id, 57);
> +			return id[54] * id[55] * id[56];
>  		else
>  			return id[1] * id[3] * id[6];
..

NAK.  That's not quite correct, either.

The LBA capacity can be larger than the CHS capacity,
so we have to use the reported LBA values if at all possible.

That's why ata_id_is_lba_capacity_ok() exists,
and why it looks so peculiar.

Some of those early drives really did require that kind of logic.

Cheers

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