[PATCHv2] nvme-mpath: delete disk after last connection

[Christoph Hellwig]

On Tue, Apr 20, 2021 at 11:14:36PM +0900, Keith Busch wrote:
> On Tue, Apr 20, 2021 at 03:19:10PM +0200, Hannes Reinecke wrote:
> > On 4/20/21 10:05 AM, Christoph Hellwig wrote:
> > > On Fri, Apr 16, 2021 at 08:24:11AM +0200, Hannes Reinecke wrote:
> > > > With the proposed patch, the following messages appear:
> > > > 
> > > >   [  227.516807] md/raid1:md0: Disk failure on nvme3n1, disabling device.
> > > >   [  227.516807] md/raid1:md0: Operation continuing on 1 devices.
> > > 
> > > So how is this going to work for e.g. a case where the device
> > > disappear due to resets or fabrics connection problems?  This now
> > > directly teards down the device.
> > > 
> > Yes, that is correct; the nshead will be removed once the last path is
> > _removed_.
> 
> The end result is also how non-multipath nvme behaves, so I think that's
> what users have come to expect.

I'm not sure that is what users expect.  At least the SCSI multipath
setups I've worked do not expect it and ensure the queue_if_no_path
option is set.

> > But key point here is that once the system finds itself in that
> > situation it's impossible to recover, as the refcounts are messed.
> > Even a manual connect call with the same parameter will _not_ restore
> > operation, but rather result in a new namespace.
> 
> I haven't looked at this yet, but is it really not possible to restore
> the original namespace upon the reestablished connection?

It is possible, and in fact is what we do.