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



On 06/26/2009 07:03 PM, Chandra Seetharaman wrote:
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 ?


I do not think you want the interface to be per vendor-product in the kernel. You might want some devices with some feature on and some with it off. In userspace we can decide if it is should be per vendor-product or per device, and then have multipath set things up. The kernel interface should probably be more generic.


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


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