Re: [PATCH 02/17] scsi_dh_alua: Disable ALUA handling for non-disk devices

[Christoph Hellwig <hch@lst.de>]

On Mon, May 11, 2015 at 12:25:51PM +0200, Hannes Reinecke wrote:
> The spec wording doesn't explicitly disallowing you from doing so
> (unless you're using referrals).
> But in realiter we're using the ALUA device handler only when
> multipathing is used, which in turn runs on disk devices only.
> So we can limit ourselves to disk devices, too.
> 
> Everything else (like tapes or tape changers) will have to
> implement their own logic anyway; tape support in multipathing
> with or without ALUA is too horrible to contemplate ...

So what is the problem you're trying to solve here?  We were attaching
to other nodes and so far I haven't heard about that being a problem.

Basically we'll disallow I/O for offlines paths to non-disk devices
once the ALUA handler is attached, which actually seems useful
even without a multipath handler on top.

> >> +	if (sdev->type != TYPE_DISK &&
> >> +	    sdev->type != TYPE_RBC &&
> >> +	    sdev->type != TYPE_OSD) {
> > 
> > And does it really allow RBC (but not ZBC)?
> > 
> Thought so, but I'll have to cross-check.
> Maybe it's time to implement a 'scsi_is_disk_type()' macro...

If the reason to disallow anything that we can't use dm-mpath on
both OSD and ZBC in it's current form are excluded.  RBC would
be included, although I doubt there is a multi ported RBC
device available.