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

On Mon, Sep 25, 2017 at 04:05:17PM +0200, Hannes Reinecke wrote:

On 09/25/2017 03:50 PM, Christoph Hellwig wrote:

quoted

On Mon, Sep 25, 2017 at 03:47:43PM +0200, Hannes Reinecke wrote:

quoted

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)