[PATCHv3] nvme-mpath: delete disk after last connection

[Keith Busch]

On Tue, May 04, 2021 at 12:54:14PM -0700, Sagi Grimberg wrote:
> 
> > > As stated in the v3 review this is an incompatible change.  We'll need
> > > the queue_if_no_path attribute first, and default it to on to keep
> > > compatability.
> > > 
> > 
> > That is what I tried the last time, but the direction I got was to treat
> > both, NVMe-PCI and NVMe-oF identically:
> > (https://lore.kernel.org/linux-nvme/34e5c178-8bc4-68d3-8374-fbc1b451b6e8@grimberg.me/)
> 
> Yes, I'm not sure I understand your comment Christoph. This addresses an
> issue with mdraid where hot unplug+replug does not restore the device to
> the raid group (pci and fabrics alike), where before multipath this used
> to work.
> 
> queue_if_no_path is a dm-multipath feature so I'm not entirely clear
> what is the concern? mdraid on nvme (pci/fabrics) used to work a certain
> way, with the introduction of nvme-mpath the behavior was broken (as far
> as I understand from Hannes).
> 
> My thinking is that if we want queue_if_no_path functionality in nvme
> mpath we should have it explicitly stated properly such that people
> that actually need it will use it and have mdraid function correctly
> again. Also, queue_if_no_path applies really if all the paths are
> gone in the sense they are completely removed, and doesn't apply
> to controller reset/reconnect.
> 
> I agree we should probably have queue_if_no_path attribute on the
> mpath device, but it doesn't sound right to default it to true given
> that it breaks mdraid stacking on top of it..

If you want "queue_if_no_path" behavior, can't you just set really high
reconnect_delay and ctrl_loss_tmo values? That prevents the path from
being deleted while it is unreachable, then restart IO on the existing
path once connection is re-established.