nvme reservation commands during controller reset

[Christoph Hellwig]

On Tue, Aug 11, 2020 at 01:48:20PM -0700, Sagi Grimberg wrote:
> 
> > > We saw that in case of path error, nvme reservation cmds does not get error handling.
> > > This is true via the blk layer as well as nvme-cli.
> > > 
> > > We are working on implementing nvmeof stack and
> > > this current behavior is blocking our host from running nvme reservation cmds during path error.
> > 
> > What's blocking you from retrying this command in your host software?
> > 
> > If we truly want to provide a way to hide intermittent errors on
> > passthrough commands via automatic retry, it may be a little longer
> > before such an interface hits a released kernel.
> 
> I think we need to keep the passthru commands as they are, but
> reservations coming from the pr_ops maybe we can failover these
> in nvme_pr_command?

Yes, if issued from the multipath device we should try another path.

> 
> What is the semantics in scsi btw? Didn't see any failover functionality
> for pr_ops...

SCSI has no native failover support, but dm-multipath should support
this.