Re: [PATCH 2/5] scsi_scan: Restrict sequential scan to 256 LUNs

[Hannes Reinecke <hare@suse.de>]

On 03/27/2014 07:49 AM, Christoph Hellwig wrote:
> On Tue, Dec 10, 2013 at 12:05:12PM +0100, Hannes Reinecke wrote:
>> Sequential scan for more than 256 LUNs is very fragile as
>> LUNs might not be numbered sequentially after that point.
>>
>> SAM revisions later than SCSI-3 impose a structure on
>> LUNs larger than 256, making LUN numbers between 256
>> and 16384 illegal.
>> SCSI-3, however allows for plain 64-bit numbers with
>> no internal structure.
>>
>> So restrict sequential LUN scan to 256 LUNs and add a
>> new blacklist flag 'BLIST_SCSI3LUN' to scan up to
>> max_lun devices.
>
> What do you need the blacklist flag for?  There's no user of it, and
> supporting that many LUNs without REPORT LUNS support doesn't sound very
> practical anyway.
>
Because there is no guarantee that pre-SCSI-3 devices (or devices 
announcing to be pre-SCSI-3) will not allow to scan more than 256 devices.
Thinking of older Symmetrix here with their weird 'SPC-3 masking as 
SCSI-2' habit.

Also currently we're allowing to scan beyond 256 without any 
restrictions there might be installations out there which rely on this 
behaviour.

Hence this flag.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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