linux-kernel - Re: [PATCH 1/2] virtio-scsi: fix parsing of hotplug/hot-unplug LUN number

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Message-ID: <50111936.8090508@acm.org>
Date:	Thu, 26 Jul 2012 10:17:26 +0000
From:	Bart Van Assche <bvanassche@....org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/2] virtio-scsi: fix parsing of hotplug/hot-unplug LUN
 number

On 07/26/12 09:21, James Bottomley wrote:
> On Thu, 2012-07-26 at 11:04 +0200, Paolo Bonzini wrote:
>> Il 26/07/2012 10:52, James Bottomley ha scritto:
>>>>> +static unsigned int virtscsi_get_lun(u8 *lun_bytes)
>>>>> +{
>>>>> +	unsigned int lun = (lun_bytes[2] << 8) | lun_bytes[3];
>>>>> +	return lun & 16383;
>>>>> +}
>>>>> +
>>> Why are you rolling your own incomplete version of scsilun_to_int here?
>>
>> Because scsilun_to_int does not do the AND, so it would have exactly the
>> same bug I'm fixing.
> 
> It's not a bug ... it's the encoding.  All the other devices use this
> too.  Ideally we should have switched to 64 bit lun numbers for the
> encoding to be exact, but nothing so far has gone over 32 bits.  If we
> don't encode the Address method as part of the lun number, we don't get
> the reverse transform right and the addressing often fails.
> 
> That does mean that arrays that use address method=1 in REPORT LUNS have
> their lun numbers start at 16384.

Has it already been considered to modify scsilun_to_int() such that LUN
numbers start at zero even for addressing method 1 ? This is what e.g.
the function scst_unpack_lun() already does. See also
http://scst.svn.sourceforge.net/viewvc/scst/trunk/scst/src/scst_lib.c?revision=HEAD&view=markup.

Bart.
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