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

From: Chandra Seetharaman <sekharan@us.ibm.com>
To: device-mapper development <dm-devel@redhat.com>
Cc: 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 17:03:36 -0700	[thread overview]
Message-ID: <1246061016.14164.45.camel@chandra-ubuntu> (raw)
In-Reply-To: <1246046154.3925.80.camel@mulgrave.site>

On Fri, 2009-06-26 at 14:55 -0500, James Bottomley wrote:
> 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.
> 
> One way around this might simply be to make the device_handlers create a
> sysfs interface for additional parameters.  Then the multipath command

Yes, having a per device interface is one of the options we considered.
Once we have that defined we can either use sysfs or a scsi_dh_8() API
to achieve the same.

But we wanted to have it per vendor-product instead of per device, I
don't recall the problems associated with it. Mike(C), do you recall ?

> can feed them (or in a pinch, users relying on the features can pass
> them in manually).  Right at the moment having no possible work around
> does appear to be an issue.

I will try to roll up a patch soon.
> 
> James
> 
> 
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel