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

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Message-ID: <4999F0B8.7020700@rtr.ca>
Date:	Mon, 16 Feb 2009 18:03:20 -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

Mark Lord wrote:
> 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.
..

Mind you, one can do better than that, too.

The "10% solution" in there right now is a bit of a (working) hack.
It really probably just needs to check for a flipped-LBA
that is within +/- one full cylinder of the CHS capacity.

Cheers
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