Re: [PATCH 4/4] sd: Handle ZBC drives correctly

[Hannes Reinecke <hare@suse.de>]

On 07/21/2014 01:29 PM, Christoph Hellwig wrote:
> On Mon, Jul 21, 2014 at 10:27:21AM +0200, Hannes Reinecke wrote:
>> ZBC drives are close to disk devices, so update sd.c to handle
>> ZBC drives correctly.
>
> While the other patches all look fine with me I strongly disagree with
> this one.  Devices reporting the ZBC device type must have sequential
> required zones, so they are _not_ anywhere close to disk devices,
> and writes to them will cause errors that we aren't evenable able to
> handle yet.
>
> If it makes some sort of experiment easier for you we can add a way to
> force ZBC devices to use sd.c conditionally.  Do you have a test device
> that this works with?
>
Yes, I have.

I was actually considering implementing a module option for sd
(eg attach_zbc) to allow zac/zbc devices to be attached to the sd 
driver.
Which will be off per default, so your concern should be addressed.

However, zbc devices _are_ similar to normal 'sd' devices; it's only 
that some commands might fail unexpectedly.
But all the usual commands from sbc are supported, so I found it a 
bit odd having to implement my own device driver (which would be a 
clone of 'sd' anyway).

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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