linux-kernel - Re: [PATCH 1/1] scsi: retrieve cache mode using ATA

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Date:	Mon, 12 Dec 2011 16:51:07 +0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Amit Sahrawat <amit.sahrawat83@...il.com>
Cc:	Nam-Jae Jeon <namjae.jeon@...sung.com>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] scsi: retrieve cache mode using ATA_16 if normal
 routine fails

On Mon, 2011-12-12 at 16:48 +0530, Amit Sahrawat wrote:
> It has been observed that a number of USB HDD's do not respond correctly
> to SCSI mode sense command(retrieve caching pages) which results in their
> Write Cache being discarded by queue requests i.e., WCE if left set to
> '0'(disabled).
> This results in a number of Filesystem corruptions, when the device
> is unplugged abruptly.

Um, how would knowing the caching type correctly help?  If you surprise
unplug the device, we can't send a flush to it anyway ...

> So, in order to identify the devices correctly - give it
> a last try using ATA_16 after failure from normal routine.
> Introduce a mechanism to store write-cache type using /sys/class/
> interface, so that the normal code continues to function without errors.
> 
> Signed-off-by: Amit Sahrawat <amit.sahrawat83@...il.com>
> Signed-off-by: Nam-Jae Jeon <namjae.jeon@...sung.com>

This whole patch looks like a layering violation.  Why not just update
the SAT layer to translate the MODE SENSE correctly?

James


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