[PATCH 8/9] nvme: implement multipath access to nvme subsystems

[Keith Busch]

On Mon, Sep 25, 2017 at 04:05:17PM +0200, Hannes Reinecke wrote:
> On 09/25/2017 03:50 PM, Christoph Hellwig wrote:
> > On Mon, Sep 25, 2017 at 03:47:43PM +0200, Hannes Reinecke wrote:
> >> Can't we make the multipath support invisible to the host?
> >> IE check the shared namespaces before creating the device node, and just
> >> move them under the existing namespaces if one exists?
> > 
> > That was what my first version did, but various people talked me
> > out of it.  Unfortunately just multiplexing breaks a few things,
> > including the userspace passthrough ioctls.
> > 
> Care to give some specifics?
> How would userspace passthrough be affected?

Ioctls aside, if you've only one disk handle, it's a little difficult to
compare iostats on each path, which can be useful for diagnosing issues.

> I would've thought that we're sending the ioctl down one path, and we'd
> be getting the completion back on the same path/queue/whatever.
> (Unless we're talking multi-command ioctls, but those are evil anyway)