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Re: [Qemu-ppc] [PATCH] scsi-bus: fix endianness bug in store_lun()

From: Benjamin Herrenschmidt
Subject: Re: [Qemu-ppc] [PATCH] scsi-bus: fix endianness bug in store_lun()
Date: Sat, 16 Mar 2013 14:01:27 +0100

On Sat, 2013-03-16 at 23:11 +1100, Alexey Kardashevskiy wrote:
> > No, LUNs are composed of four 2-byte big-endian values.
> I cannot find it in "SCSI Commands References Manual"
> (for example here - 
> http://www.seagate.com/staticfiles/support/disc/manuals/Interface%
> 20manuals/100293068c.pdf 
> ). It just says that it is 8 bytes per
> LUN and SCSI itself is big endian. Could you please point me to
> the correct spec?

The confusion comes from the old SCSI protocol LUN as a 2 bytes number
identifying a unit for a given bus/device and the "new style" LUN as a
more generic concept such as used in SRP (ie vscsi is SRP) which
encompass the bus, ID and LUN in one big number.

The actual type of LUN returned by REPORT_LUN depends on the
SELECT_REPORT field (I don't remember the details, but the doco you
point to say to see what's in SAM-4) and the result is *variable* in
size, so it should be kosher for qemu to just return 2 bytes as long as
the LUN_LIST_LENGTH field of the reply is correct.

So it all needs a bit of double checking but I wouldn't be surprised if
at the end of the day the culprit was my SLOF code :-)


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