Re: [PATCH] scsi: Allow 64-bit LUNs during report lun scan

[Hannes Reinecke <hare@suse.de>]

On 02/14/2013 07:02 PM, Jeremy Linton wrote:
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> On 2/13/2013 9:38 PM, James Bottomley wrote:
>> Yes.  The two functions are simple transforms ensuring that we can pack up
>> to two levels of luns into a u32 whatever address method is used.  At the
>> time it was done, no array or other extant system went beyond this.
>>
>> At the end of the day, a LUN is just a handle, so even if we go to 64 bits
>> we're still going to be packing the address method into the logical unit
>> "number".
>
> 	Ok, I will buy that (probably violates SAM5, 4.7.1, but no big deal), two
> points.
>
> 	First this requires basically every adapter capable of recieving address
> method!=0 LUNs to set the 64-bit capable flag that is included in this patch.
> Otherwise the "scsi: %s lun%d has a LUN larger than allowed by the host
> adapter\n" path fires even for a small number of luns because the address
> method bit creates a "lun" > max_luns in all cases.
>
Hehe. As we're down to nitpicking:
The 'support_64bit_luns' is a _hardware_ flag.
Some HBA hardware (SPI, and most RAID HBAs) simply do not have the 
facilities to _send_ 64bit LUNs; SPI HBAs in most cases simply 
reserve a byte for the LUN.

So irrespective of what response they'll be getting via REPORT_LUNS 
they lack the possibility of addressing all of them.
And for those we need the 'max_luns' setting.

>
>
> 	Second, its possible with address method 11b, that none of the devices are
> actually visible even with this patch, as a device that chooses to use address
> method=11b and one of the >16 bit addressing methods gets its LSB truncated by
> the 32-bit return from scsilun_to_int(). Not that I have see one of those, no
> one needs that many LUNs <chuckle>. So, the flag in this patch is somewhat
> misnamed as it doesn't really support 64-bit luns. To stick to the existing
> method scsilun_to_int needs to be u64.
>
Correct. This I'll be addressing with a later patch, moving 'lun' to 
full 64bit.

>
> 	BTW: Tiny syntax cleanup, scsilun_to_int() should have a return type of
> unsigned.
>
Will be cleaned up with the next round of patches.

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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