Re: [Scst-devel] Fwd: Re: linuxcon 2010...
From: Vladislav Bolkhovitin
Date: Mon Aug 30 2010 - 16:47:44 EST
Nicholas A. Bellinger, on 08/29/2010 12:47 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.
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.
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".
Sorry, but this is just more generic handwaving on your part. What
constitutes a 'drop in replacement' for STGT is a decision that was to
be made by the STGT developers, not by you. target_core_stgt.c is an
extraordinarly transparent method of bringing drivers/scsi/scsi_tgt_*
logic into the TCM Core HBA/DEV design, and allows us to build upon and
improve the existing mainline kernel code.
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.
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. 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.
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?
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?
Thanks,
Vlad
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