Message-ID: <4C7FFD1A.8090509@vlnb.net>
Date:	Thu, 02 Sep 2010 23:38:02 +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 08/31/2010 01:46 AM wrote:
>>> Sorry, but you are completely wrong here.  This has nothing to do with a
>>> question of STGT kernel 'ABI compatibility' (because there is only one
>>> mainline user!), but has everything to do with being able to expose TCM
>>> kernel level SPC-4 emulation, and make this logic available to existing
>>> userspace fabrics in tgt.git.  Again, we are talking about userspace
>>> STGT fabric module<->   TCM kernel backstore support for .37, which has
>>> already been merged by into tgt.git, and being used by other STGT users
>>> for SG_IO and BSG passthrough.
>>
>> You are proving that I'm actually right ;). In the beginning of this
>> thread I offered a transition path from STGT to SCST and James rejected
>> it, because it didn't confirm a requirement that a new SCSI target
>> infrastructure must be STGT ABI compatible. But latter James left this
>> decision up to the STGT developers and now you are confirming that they
>> don't see any ABI compatibility issues, so my transition path fully
>> confirms all the requirements.
>
> Again, I still have no idea what you are trying to conjour up.  The
> passthrough for STGT compatibility with TCM_Loop via SG_IO and BSG has
> already been merged by Tomo-san into tgt.git.  Futhermore, we are using
> the same TCM_Loop high level multi-fabric WWPN emulation together with
> new (and old) QEMU HBA emulation into KVM guest using SG_IO and BSG as
> well.

The patches were good, but don't mislead people about that. For sake of 
clearness, what you called "the passthrough for STGT compatibility with 
TCM_Loop via SG_IO and BSG" has nothing with LIO/TCM_Loop. What merged 
fixed problems STGT had in the pass-through implementation. It at the 
same time fixed problems with SCST's scst_local, so similarly can be 
called "the passthrough for STGT compatibility with scst_local via SG_IO 
and BSG".

The same is for the second half of the above. It's for scst_local in the 
same degree as for TCM_Loop.

>> I'm not deciding anything, I'm only analyzing and seeing a contradiction:
>>
>> 1. James wants only one SCSI target infrastructure in the kernel.
>>
>> 2. If drivers/scsi/scsi_tgt_*.c left after the merge of the new SCSI
>> target infrastructure, it would mean that STGT left as well =>  2 SCSI
>> target infrastructure in the kernel.
>>
>> For me it doesn't matter. I just want clear rules, hence asking for
>> clarification.
>
> Seriously, arguing over the use of people's language from weeks ago once
> the decision has already been made to move forward is really of little
> value at this point.

Does it look I'm arguing? Again, I'm analyzing and asking for 
clarification in the contradictions I see. I don't like when such 
important decisions are done behind closed doors and kept in a secret.

>>> It is obvious to even an casual observer from watching the TCM/LIO patch
>>> series that have been flying across the linux-scsi wire the last 24
>>> months that the major features (including PR and ALUA, and new fabric
>>> module drivers) have been developed individual feature bit by feature
>>> bit using a distributed git workflow in a bisectable manner.  Each
>>> series was produced in such a manner that each patch could be reviewed
>>> individually by those interested parties.
>>
>> That's a nice, but quite meaningless LIO advertisement. SCST is using
>> the same bisectable, distributed and reviewable workflow.
>
> Actually, that is incorrect.  Your project uses a centralized
> development model, which has it's obvious limitiations in terms of
> speed, flexability, and community scale.  But really, don't take my word
> for it, you can hear it for yourself directly from the horse's mouth
> here:
>
> http://www.youtube.com/watch?v=4XpnKHJAok8
>
> I also very strongly suggest you find a transcript of this talk so you
> can really understand what Linus means here wrt to a distributed
> development workflow.

Well, Nicholas, are you really understanding what you are writing? We in 
our projects have fully the same distributed (or centralized, if you 
like it) development model. Have you noticed how many developers SCST 
project has? We have our responsibility areas (target drivers, 
scstadmin, etc.) and commit in them. The way how we get updates for the 
rest of the kernel doesn't matter. Git is better for such huge projects 
as the kernel, but for our relatively small and centralized by nature 
due to small size (sub)projects it doesn't matter and won't bring any value.

Actually, to have all in one place without the rest of the kernel is 
more convenient, because grep over few MBs is a lot faster than over the 
few hundreds of MBs of the full kernel sources.

>>   If we had a
>> kernel.org git account, we would use it as well, but so far we are happy
>> with SF.net hosting. BTW, how was you able to get the git account
>> without a single patch merged in the kernel? You must have good
>> connections in the kernel community.
>
> Please don't turn this into a kernel.org vs. SF.net thing..  There are
> plenty of places that offer free git hosting (see github)

SF.net for a long time has been offering git hosting, but we don't see 
reasons to move to it. SVN has all we need. We are not (yet) so big to 
need git.

But, we can move to git at any moment as soon as it is needed, for 
instance, because of SCST merged in the mainline kernel.

>>> This is the big difference between our respective development processes.
>>> This is the case not only for SCSI feature bits that TCM/LIO and SCST
>>> share, but for features in TCM/LIO v4 that are unique and not available
>>> in any other target implemention, anywhere.  And yes, I am most
>>> certainly talking about code beyond just the SCSI level fabric emulation
>>> bits you are mentioning above.
>>
>> Can you list us benefits for an average user of that work?
>
> Well, amougst the biggest advantages is actually having a sane ConfigFS
> interface that can represent the parent / child relationship between
> data structures across multiple LKMs.

Does STGT represent it in an insane manner?

> Not only does this give us a
> proper representation of TCM and fabric data structures that can be
> accesses directly by an advanced user in /sys/kernel/config/target/, it
> also provides an ideal foundation to build 1) a userspace library in
> intrepted languages and 2) create high level applications using said
> userspace libraries that allow compatiblity to be contained in the lib
> below.
>
> But wrt to actual kernel code (because this is a kernel list), the
> shortlog for the RFC posting below nicely sums up what TCM v4 is
> bringing to the table:
>
> http://lkml.org/lkml/2010/8/30/88

I have no doubts in benefits to TCM. But I have asked about benefits 
_for an average user_. STGT already can do what you listed above.

Also what advantages and additional value it has over what SCST 
*already* provides since 2007?

>>>> 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.
>>>>
>>>
>>> Then I suggest you learn a better way of communicating your ideas if you
>>> really want to work with members of the LIO/STGT development
>>> communities.
>>>
>>> First, I suggest you start explaining your ideas with actual kernel code
>>> that is 1) human readable and 2) presented in such a manner that makes
>>> it accessable for others with skills possibly different (and greater)
>>> than your own to review and give feedback.
>>
>> I have sent patches twice, the second time few months ago. Weren't they
>> human readable and accessible for kernel developers who are experts in
>> dealing with sent by e-mail patches?
>
> I think a proper kernel subsystem maintainer workflow has to do alot
> more to do these days than just sending patches over email, than it did
> say 10 years ago.  Like it or not, git is the language of the mainline
> kernel development process, and trying to imagine a *new* kernel
> subsystem maintainer (besides say, someone like akpm) not using git is
> quite a stretch of the imagination at this point.

So, do you believe that as soon as we migrate to git all the obstacles 
for the SCST merge would be immediately removed?

Thanks,
Vlad
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