Re: [PATCH 2/3] Add EVPD page 0x83 to sysfs

Hannes Reinecke
2014-03-07T13:39:34Z

On 03/07/2014 12:01 PM, James Bottomley wrote:
> On Fri, 2014-03-07 at 11:51 +0100, Hannes Reinecke wrote:
>> On 03/07/2014 11:39 AM, James Bottomley wrote:
>>> On Thu, 2014-03-06 at 10:01 +0100, Hannes Reinecke wrote:
>>>> So the only 'proper' solution would be to add a bitmap of supported
>>>> pages; however, this would be 256 bits = 32 bytes of additional
>>>> space required for struct sdev.
>>>> Which I'm a bit reluctant do to, as it'll be a sparse array in most
>>>> cases, adding to quite some wasted space.
>>>
>>> Why per sdev? Isn't it per target? The supported EVPD page list
>>> shouldn't really vary for luns of the same target unless something very
>>> strange is happening in the array.
>>>
>> Spec says it's per LUN:
>
> Specs say a lot of "interesting" things. The question is what's common
> practise in the field.
>
>> 7.8.16 Supported VPD Pages VPD page
>> The Supported VDP Pages VPD page contains a list of the VPD page
>> codes supported by the logical unit (see
>> table 637).
>>
>> so we shouldn't really make any assumptions about what might be
>> sensible or strange.
>
> The cardreader case is the one I think causes problems for this. Going
> completely the opposite direction, why do we need to cache this at
> all? ... it's fairly simple to request each time and it avoids worrying
> about the data changing because of a change in the array.
>
Storage arrays more often than not do this, too. Especially those
which export a management device.
(block-device specific VPD pages really do not make sense on a
management device)

Cheers,

Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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