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

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Message-ID: <1343302260.3115.33.camel@dabdike>
Date:	Thu, 26 Jul 2012 15:31:00 +0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Bart Van Assche <bvanassche@....org>, 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 Thu, 2012-07-26 at 12:43 +0200, Paolo Bonzini wrote:
> Il 26/07/2012 12:33, James Bottomley ha scritto:
> >> > 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.
> > Yes, as I said before, the problem is that the actual numbers are
> > 
> > 1. not 1:1: there are several possible encodings of luns 0-255
> > 2. hierarchical, so once you go beyond a single level you can't properly
> > use a numeric representation either.
> > 
> > the mid layer just uses the lun number as an encoding of the actual SAM
> > lun.  The key for us is that int_to_scsilun has to go back the other
> > way.
> 
> I still disagree, but I will modify QEMU so that this patch is not
> necessary.  Later I can switch to int_to_scsilun.

Thanks, on the principle of least surprise, you definitely don't want
the lun numbering to change depending on whether you directly attach to
the array or pass it through virtio-scsi.

James


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