linux-kernel - Re: [Scst-devel] Fwd: Re: linuxcon 2010...

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Message-ID: <4C79484B.3090607@vlnb.net>
Date:	Sat, 28 Aug 2010 21:32:59 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:	James Bottomley <James.Bottomley@...e.de>,
	Dirk Meister <dmeister@...-paderborn.de>,
	linux-scsi@...r.kernel.org, Chetan Loke <chetanloke@...il.com>,
	Chetan Loke <generationgnu@...oo.com>,
	scst-devel <scst-devel@...ts.sourceforge.net>,
	linux-kernel@...r.kernel.org, Mike Christie <michaelc@...wisc.edu>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [Scst-devel] Fwd: Re: linuxcon 2010...

Nicholas A. Bellinger, on 08/27/2010 01:23 AM wrote:
>> Nicholas A. Bellinger, on 08/25/2010 01:23 AM wrote:
>>> As mentioned explictly earlier in this thread, my WIP code for the
>>> kernel level subsystem backstore using STGT kernel<->   user CDB
>>> passthrough logic in drivers/target/target_core_stgt.c is a item on
>>> my TODO list, but I will repeat, is NOT being tagged as a mainline
>>> .37 item.
>>
>> Hmm, I can't understand, if target_core_stgt.c is "NOT being tagged as a
>> mainline .37 item", then the STGT ABI compatibility for being a drop in
>> replacement for STGT isn't a requirement? Or am I missing something?
>
> Sorry, but I have no idea what you are trying to conjour up here.
>
> To spell out (again) the TCM/LIO<->STGT compatibility stages that have
> been persued pubically over the last months:
>
> I) Create proper userspace tgt.git SG_IO and BSG passthrough into
>     TCM_Loop v4 using high-level multi-fabric WWPN emulation so that TCM
>     Core SPC-4 kernel emulation is exposed to STGT user fabrics, eg:
>     userspace fabric module ->  kernel backstore passthrough.  (DONE
>     for .37, and STGT passthrough + BSG backstore support merged into
>     tgt.git by Tomo-san)
>
> II) Complete target_core_stgt.c TCM subsystem plugin for kernel ->  user
>      CDB ->  LUN passthrough building upon existing
>      drivers/scsi/scsi_tgt_*.c code.  (WIP for .38, made available
>      initially as a seperate standalone .ko module in lio-core-2.6.git)

That would mean that if LIO merged in .37:

1. It would be merged _without_ STGT ABI compatibility, i.e. one of the 
requirements for a new SCSI target infrastructure merge is violated.

2. It would _not_ be a drop in replacement for STGT, because STGT's 
drivers/scsi/scsi_tgt_*.c code would stay in the kernel. Those would 
effectively mean that another requirement for a new SCSI target 
infrastructure merge would be violated: there would be 2 SCSI target 
infrastructures in the kernel and any STGT in-kernel driver (for 
instance, built as an outside module) would continue working. My 
understanding of "drop in replacement" is "one out, another in at once".

Please tell me where I'm wrong? I would appreciate if you be precise and 
answer the above 2 my concerns. There is no point to again repeat what 
you have already written without adding any new information.

>>> Tomo-san, mnc, and other storage folks have been briefed on the
>>> remaining issues that would be involved to get a prototype
>>> functioning with drivers/target/target_core_stgt.c, and rough idea of
>>> what it would take in existing mainline drivers/scsi/scsi_tgt_*.c
>>> code.  With the current WIP code this will allow the userspace CDB ->
>>> LUN passthrough to function transparently with all TCM SPC-4
>>> compliant logic as a standalone struct se_subsystem_api
>>> tcm_core_stgt.ko backstore.
>>
>> This is exactly what we are discussing.
>
> Then I suggest you start working on a patch for drivers/scsi/scsi_tgt_*
> in order to address what you believe are the preceived shortcomings of
> the original design.
>
> Until you can do that, and actually take an impartial look at the
> existing drivers/scsi/scsi_tgt_*.c,  it would be a bit difficult to
> beleive you genuinely want to steer our current level of interaction
> away from continued hand-waving noise into a real rational technical
> discourse between yourself and the LIO/STGT development community.

My look is completely impartial. With all my respect, I'm just quite 
ahead of you and can see what you are unable (or don't want?) to see. I 
did what you are currently doing almost 4 years ago. I have already 
written all the necessary code and addressed all _rose on practice_ 
concerns. But all my attempts to explain my view are just blindly 
ignored without any considerations, so I have no idea how more I can 
explain it.

Thanks,
Vlad
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