[dm-devel] Re: [PATCH 7/7] scsi_dh: attach to hardware handler from dm-mpath

[James Bottomley]

On Wed, 2008-05-21 at 08:18 +0200, Hannes Reinecke wrote:
> Chandra Seetharaman wrote:
> > Hi Hannes,
> > 
> > Now I see why you want this change in dm-multipath. I think I agree with
> > these changes.
> > 
> Ah. good.
> 
> > But, it brings another question: what does dh_state provide ? Help to
> > user to see which hardware handler a device is attached to ?
> > 
> And allowing to attach to a different hardware handler.
> Not everyone is running multipathing, but might be interested in the
> having the device handler nevertheless.
> 
> > I thought more about the scsi_dh_detach function (in the context of my
> > earlier comment), adding it would require more housekeeping to associate
> > one-to-one mapping between attach and detach. We can leave it the same
> > way as the module will be detached when the device disappear eventually.
> > 
> Why? You can detach with dh_state, too; just do an
> 
> echo detach > /sys/block/sdX/device/dh_state
> 
> and the hardware handler will detach.
> So no additional attribute is required.

Actually, if you're going down this route, it makes more sense to have
the device handler be a driver ... remember you were the one promising
multiple driver binding at the FS/Storage summit ...  that way we can
use all the generic driver standard interfaces for manual
binding/unbinding.  Plus we can place the attributes as driver attribute
groups.

James