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

From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] [PATCH] scsi-bus: fix endianness bug in store_lun()
Date: Sun, 17 Mar 2013 01:10:02 +1100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130107 Thunderbird/17.0.2

On 17/03/13 00:01, Benjamin Herrenschmidt wrote:
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 -
). 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.

No, it is always 8 bytes long. Does not say anywhere that it can be of another size.

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 :-)

The patch below fixes the issue on the SLOF side. Your job? :)
So, I revert the QEMU patch then and will post this. I just
wonder if other 6 bytes are used (or can be used) anyhow by someone
but I need to find SAM-5 spec first, does not seem very easy :-/

btw why was it x@ but not address@hidden I mean yes, is it the same on ppc
but would help a lot in reading this write-only language :)

diff --git a/board-qemu/slof/vio-vscsi.fs b/board-qemu/slof/vio-vscsi.fs
index 8a150ea..88d4085 100644
--- a/board-qemu/slof/vio-vscsi.fs
+++ b/board-qemu/slof/vio-vscsi.fs
@@ -606,7 +606,7 @@ CREATE sector d# 512 allot
dup rot 0 fill ( devarray devcur ndev lunarray size mem )
         dup >r swap move r>           ( devarray devcur ndev mem )
         dup sector l@ 3 >> 0 DO       ( devarray devcur ndev mem memcur )
-           dup dup x@ j 8 << 8000 or or 30 << swap x! 8 +
+           dup dup address@hidden j 8 << 8000 or or 30 << swap x! 8 +
         LOOP drop
        rot                           ( devarray ndev mem devcur )
         dup >r x! r> 8 +              ( devarray ndev devcur )


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