linux-kernel - Re: Re: Re: BUG in kernel: Wrong Handling of USB HDD’s in scsiglue(slave_configure) and scsi/sd(sd_read_cache

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Message-ID: <CADDb1s031VX65+G-Uq-12y4qWq98-OS6DKz7mUCo=8AQkVQVTQ@mail.gmail.com>
Date:	Thu, 6 Oct 2011 01:21:11 +0530
From:	Amit Sahrawat <amit.sahrawat83@...il.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	linux-usb@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: Re: Re: BUG in kernel: Wrong Handling of USB HDD’s in scsiglue(slave_configure) and scsi/sd(sd_read_cache_type)

On Wed, Oct 5, 2011 at 10:54 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Wed, 2011-10-05 at 22:29 +0530, Amit Sahrawat wrote:
>> Can anyone suggest what is the way ahead to detect the presence of
>> Write Cache in these kind of USB HDD and proceed accordingly by
>> assigning proper flushing method.
>> Please share some opinions on this.
>
> We're a bit out of ideas.  We've already established that we do exactly
> what windows does in this situation, which is usually what we aim for.
> Realistically, if the disks lie how do we know when not to believe them?
I never knew this could turn out to be an issue with such history. But
atleast debugging helped in diagnosis.
>
> The best we could probably offer is an interface to turn on the WCE bit
> in software (technically, you can do this today
> in /scsi/class/scsi_disk/<disk>/cache_type, it's just that it will try
> to commit the change as a MODE_SELECT which will presumably fail).
Thanks James, is this related with SCSI command MODE_SELECT? and this
is to be passed when there is some failure?
or simply doing an "echo <value>" to
/scsi/class/scsi_disk/<disk>/cache_type? can you please elaborate a
little
>
> James
>
Thanks & Regards,
Amit Sahrawat
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