[Stgt-devel] [PATCH] Move device type to LUN

[FUJITA Tomonori]

From: FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp>
Subject: Re: [Stgt-devel] [PATCH] Move device type to LUN
Date: Fri, 15 Jun 2007 13:36:12 +0900

> From: Hannes Reinecke <hare at suse.de>
> Subject: Re: [Stgt-devel] [PATCH] Move device type to LUN
> Date: Tue, 12 Jun 2007 14:44:03 +0200
> 
> > FUJITA Tomonori wrote:
> > > From: Hannes Reinecke <hare at suse.de>
> > > Subject: Re: [Stgt-devel] [PATCH] Move device type to LUN
> > > Date: Mon, 11 Jun 2007 17:15:19 +0200
> > > 
> > >> Pete Wyckoff wrote:
> > >>> hare at suse.de wrote on Tue, 05 Jun 2007 15:38 +0200:
> > >>>> This patch moves the device type down to the LUN structure.
> > >>>> And in doing so we now also have the proper peripheral device
> > >>>> type and peripheral device qualifier attributes for the INQUIRY
> > >>>> data.
> > >>> Makes sense to me too.
> > >>>
> > >>>> One thing puzzles me, though: do we support commands with no
> > >>>> LUN attached to it? IE is it valid to have 'cmd->dev == NULL'?
> > >>>> If so: where is the point here? If that's our handling of a
> > >>>> non-existing LUN 0 we should rather add a proper LUN 0 and
> > >>>> treat cmd->dev == NULL as an error case ...
> > >>> In the SCSI model, every device must have at least one LUN for
> > >>> handling REPORT LUNS and a couple other commands.  It is addressed
> > >>> as LUN 0 or using the "well-known" LUN for the command.  In the stgt
> > >>> abstraction, though, there is no magic LUN like this.  Instead
> > >>> things like spc_inqury use cmd->dev == NULL to handle this case.
> > >>>
> > >> Ah. Hence.
> > >>
> > >>> Perhaps it is reasonable to create a special device for these
> > >>> commands.  Up in target.c, you could assign cmd->dev to target->dev,
> > >>> where that is the special device, paralleling the way that
> > >>> target->cmd_queue is used.  As a side effect, lots of "if (cmd->dev)
> > >>> ... else ILLEGAL_REQUEST" clauses can be removed from device code
> > >>> too.
> > >>>
> > >> Well, I actually thought of creating a proper LUN 0 with type 0xc.
> > > 
> > > We still need to handle cmd->dev == NULL case though probably we can
> > > remove cmd->dev == NULL case in device type code.
> > > 
> > > I don't have storage systems that work in your way. Is it common?
> > > 
> > > 
> > Yes, quite common. HP and EMC (to name but a few) do it this way.
> > Most storage arrays actually refuse to attach any devices to LUN0, as
> > this is a pure management LUN.
> > 
> > I will draft up a patch which creates a proper controller LUN0.
> 
> Ok, here's a patch. This depends on the patch that I've just
> submitted.
> 
> This adds scc support and fixes ibmvio. iSCSI works. ibmvio works for
> me, but it detects scsi devices in a unique way, so I'm not sure it
> works for everyone.
> 
> As described, a scsi controler device is automatically created as lun0
> with a new target.
> 
> lily:/home/fujita# ./tgt/usr/tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.2001-04.com.example:storage.disk2.tulip.sys1.xyz
> lily:/home/fujita# ./tgt/usr/tgtadm --op show --mode target
> Target 1: iqn.2001-04.com.example:storage.disk2.tulip.sys1.xyz
>     System information:
>         Driver: iscsi
>         Status: running
>     I_T nexus information:
>     LUN information:
>         LUN: 0
>             Type: raid
>             SCSI ID: deadbeaf1:0
>             SCSI SN: beaf10
>             Size: 0
>             Backing store: No backing store
>     Account information:
>     ACL information:
> 
> 
> The patch is still very hacky but shows how it works. Let me know this
> works or not.

I did some cleanups.

http://git.kernel.org/?p=linux/kernel/git/tomo/tgt.git;a=shortlog;h=scc