[PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands

[Christoph Hellwig]

On Tue, Jul 12, 2022 at 11:13:57PM +0300, Sagi Grimberg wrote:
> I think the difference from scsi-generic and controller nvme passthru is
> that this is a mpath device node (or mpath chardev). This is why I think
> that users would expect that it would have equivalent multipath
> capabilities (i.e. failover).

How is that different from /dev/sg?

> In general, I think that uring passthru as an alternative I/O interface
> and as such needs to be able to failover. If this is not expected from
> the interface, then why are we exposing a chardev for the mpath device
> node? why not only the bottom namespaces?

The failover will happen when you retry, but we leave that retry to
userspace.  There even is the uevent to tell userspace when a new
path is up.