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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 07-11-2012, 10:27 AM
Alasdair G Kergon
 
Default dm mpath: add 'default_hw_handler' feature

On Wed, Jun 27, 2012 at 08:16:55AM +0200, Hannes Reinecke wrote:
> On 06/26/2012 08:32 PM, Mike Snitzer wrote:
> > When specifying the feature 'default_hw_handler' multipath will use
> > the currently attached hardware handler instead of trying to attach the
> > one specified during table load. If no hardware handler is attached the
> > specified hardware handler will be used.
> >
> > Leverages scsi_dh_attach's ability to increment the scsi_dh's reference
> > count if the same scsi_dh name is provided when attaching -- currently
> > attached scsi_dh name is determined with scsi_dh_attached_handler_name.
> >
> > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > Tested-by: Babu Moger <babu.moger@netapp.com>
> > Reviewed-by: Chandra Seetharaman <sekharan@us.ibm.com>
> Looks good.

Maybe, but I'd like to see an inline explanation of what this confusing new
setting means and a better patch header that provides some motivation for this
change.

To my eyes, the word "default" is over-used here. If I *don't* specify the new
"default" flag, surely I'll get default behaviour, won't I, by definition? And
if I do specify it, I'm asking for default behaviour too, so isn't it
redundant?

Alasdair

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Old 07-11-2012, 01:20 PM
Mike Snitzer
 
Default dm mpath: add 'default_hw_handler' feature

On Wed, Jul 11 2012 at 6:27am -0400,
Alasdair G Kergon <agk@redhat.com> wrote:

> On Wed, Jun 27, 2012 at 08:16:55AM +0200, Hannes Reinecke wrote:
> > On 06/26/2012 08:32 PM, Mike Snitzer wrote:
> > > When specifying the feature 'default_hw_handler' multipath will use
> > > the currently attached hardware handler instead of trying to attach the
> > > one specified during table load. If no hardware handler is attached the
> > > specified hardware handler will be used.
> > >
> > > Leverages scsi_dh_attach's ability to increment the scsi_dh's reference
> > > count if the same scsi_dh name is provided when attaching -- currently
> > > attached scsi_dh name is determined with scsi_dh_attached_handler_name.
> > >
> > > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > > Tested-by: Babu Moger <babu.moger@netapp.com>
> > > Reviewed-by: Chandra Seetharaman <sekharan@us.ibm.com>
> > Looks good.
>
> Maybe, but I'd like to see an inline explanation of what this confusing new
> setting means and a better patch header that provides some motivation for this
> change.
>
> To my eyes, the word "default" is over-used here. If I *don't* specify the new
> "default" flag, surely I'll get default behaviour, won't I, by definition? And
> if I do specify it, I'm asking for default behaviour too, so isn't it
> redundant?

"default" is in reference to the hardware handler that will get attached
by the scsi_dh .match(). It has nothing to do with the userspace
multipath-tool's desired handler.

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