Re: [dm-devel] mechanism for multipath to pass information to hardware handler

From: Eddie Williams <Eddie.Williams@steeleye.com>
To: sekharan@linux.vnet.ibm.com,
	device-mapper development <dm-devel@redhat.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
	SCSI development list <linux-scsi@vger.kernel.org>,
	asson_ronald <asson_ronald@emc.com>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	Mike Christie <mchristi@redhat.com>,
	"Benoit, Arthur" <Benoit_Arthur@emc.com>
Subject: Re: [dm-devel] mechanism for multipath to pass information to hardware handler
Date: Fri, 26 Jun 2009 16:01:57 -0400	[thread overview]
Message-ID: <1246046517.6707.57.camel@eddie-laptop> (raw)
In-Reply-To: <1246045509.14164.33.camel@chandra-ubuntu>

The problem is easy to duplicate using sg_persist to register/reserve
paths to a Clariion array and then fail the active path.  The "enable"
path will fail to become active when the HONOR RESERVATION flag is not
set.  Given of course that you have a Clariion array handy...

One question I have asked EMC is in what situations would you NOT want
to set this bit?  

I can test out any changes you make in my test rig and I can probably
get the folks in the EMC lab I work with to test it as well.

Eddie

On Fri, 2009-06-26 at 12:45 -0700, Chandra Seetharaman wrote:
> Yes, Mike Christie and I were aware of this and it was one of the issue
> we were trying to resolve before we pushed scsi_dh interface upstream.
> (It is little complicated as we need the parameters to be set per
> vendor-product tuple).
> 
> The original code I ported to scsi_dh interface was from Ed Goggin(who
> was working for EMC then). IIRC, he was also aware of this issue.
> 
> When we pushed scsi_dh interface, we did get few of the EMC folks (on
> Cc) to review/test the code and they did, and this issue was not seen as
> a problem. 
> 
> We wanted to get back to that issue sometime later, got busy with other
> things, and it disappeared from my list of things-to-do as the
> regression was not seen as an issue (till now :)... I will get back to
> it.
> 
> chandra
> 
> On Fri, 2009-06-26 at 14:10 -0500, James Bottomley wrote:
> > On Wed, 2009-06-24 at 13:14 -0400, Eddie Williams wrote:
> > > I notice in scsi_dh_emc.c that there is a comment:
> > > 
> > > TODO: need some interface so we can set trespass values
> > > 
> > > I don't see where any such interface has been developed or even any
> > > discussion on the different mailing lists to create such an interface.
> > > Did I miss something?
> > > 
> > > As it stands now there is no way that I can see to have the emc hardware
> > > handler support the "honor trespass" feature short of recompiling the
> > > module forcing the flag to be set.  This leaves a feature that worked in
> > > earlier versions of multipath not working now.
> > 
> > OK so as I understand it that means that the line
> > 
> > hardware handler "1 emc 0 1"
> > 
> > now fails to function correctly because dm-emc no longer exists.  That
> > makes this a functionality regression from 2.6.26 because of this
> > commit:
> > 
> > 
> > commit cb520223d7f22c5386aff27a5856a66e2c32aaac
> > Author: Chandra Seetharaman <sekharan@us.ibm.com>
> > Date:   Thu May 1 14:50:34 2008 -0700
> > 
> >     [SCSI] scsi_dh: Remove hardware handlers from dm
> >     
> >     This patch removes the 3 hardware handlers that currently exist
> >     under dm as the functionality is moved to SCSI layer in the earlier
> >     patches.
> > 
> > Because we haven't actually moved all the functionality.
> > 
> > James
> > 
> > 
> > 
> 
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