linux-kernel - Re: [RFC PATCH 0/19] A kernel-level configfs enabled generic target engine for Linux v2.6.32

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Message-ID: <4AAE907E.1020205@vlnb.net>
Date:	Mon, 14 Sep 2009 22:50:38 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Hannes Reinecke <hare@...e.de>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	Joel Becker <joel.becker@...cle.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Florian Haas <florian.haas@...bit.com>,
	Philipp Reisner <philipp.reisner@...bit.com>
Subject: Re: [RFC PATCH 0/19] A kernel-level configfs enabled generic target
 engine for Linux v2.6.32

Nicholas A. Bellinger, on 09/12/2009 05:55 AM wrote:
> Greetings all,
> 
> This is my humble request for review and inclusion of
> Target_Core_Mod/ConfigFS v3.2 from lio-core-2.6.git code into mainline
> v2.6.32.  With TCM v3.2, the two major SPC-4 SCSI target mode fabric
> features that have now been completed: Persistent Reservation APTPL and
> implict/explict ALUA are the first all optional SPC4 defined feature
> implementation of PR and ALUA in the Linux OSS target theatre using an
> upstream user-driven virtual filesystem directory hierarchy structure
> based on configfs that can be configured in realtime in combination with
> interpreted userspace code.
> 
> Both of these new features are now being used to provide Persistent Reservations
> across target power loss and asymmetric multipath I/O to both Linux and non-Linux
> clients.  There is also an optional ALUA transition delay logic that has been
> included to futher debug and improve existing upstream client side Linux kernel code
> using TCM v3.2. These patches have been diffed against v2.6.31, and tested on x86
> 32-bit HVM, x86_64 KVM, and powerpc.
> 
> There is cleanup work continuing to make the TCM code to use dprintk(),
> and some include cleanups, and other minor fixes.  The code has also
> been run through checkpatch again since the posting in April, and all
> errors have been removed, with the exception of one ConfigFS macro
> define triggering a checkpatch false positive.
> 
> As with the posting of the TCM v3.0 code earlier in April, I have
> decided to break up the submissions into the generic target_core_mod
> piece (this patch series) and then a seperate one that will be appearing
> in the next days for v3.2 of the LIO-Target iSCSI fabric module.
> 
> More Information about Target_Core_Mod/ConfigFS, and PR and ALUA:
> 
> http://www.linux-iscsi.org/index.php/Target_Core_Mod/ConfigFS
> http://www.linux-iscsi.org/index.php/Persistent_Reservations
> http://www.linux-iscsi.org/index.php/ALUA
> 
> The complete v3.x TCM CLI operations set can be found here:
> 
> http://www.linux-iscsi.org/index.php/Lio-utils#v3.1_TCM_CLI_operations
> 
> Instructions and examples for getting setup:
> 
> http://linux-iscsi.org/builds/docs/LIO-3.0-Users_Reference_Manual.pdf
> http://www.linux-iscsi.org/index.php/Howto#Start_target_core_mod

Some questions among many I have:

1. Where and how TCM is better over the existing mainline target 
framework STGT to justify such a move as adding a new piece of code 
doing the same job?

2. On the linux-iscsi.org main page (BTW, the comparison on that page 
isn't fully correct about STGT and SCST) you claim that TCM is a generic 
target engine. But how can you prove (and test) that if there are no 
hardware target drivers for TCM?

Also patch 7 implements MIBs through procfs. Procfs is for long time 
forbidden for adding anything like that, so you can't push it in the 
mainline.

Vlad
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