Re: [PATCH 4/5] nvme: implement multipath access to nvme subsystems

On Thu, Nov 09, 2017 at 04:44:32PM +0100, Hannes Reinecke wrote:

- We don't have the topology information in sysfs;

We have all the topology information in sysfs, but you seem to look
for the wrong thing.

while the namespace
device has the 'slaves' and 'holders' directories, they remain empty,
and the path devices don't even have those directories. I really would
like to see them populated to help things like dracut figuring out the
topology when building up a list of modules to include.

Of course there aren't because there is not block device you can hold
for the controller.  

- The patch doesn't integrate with the 'claim' mechanism for block
devices, ie device-mapper might accidentally stumble upon it when
traversing devices.

Same as above.  There is no block device to be claimed.

I'll be sending two patches to resurrect the 'bd_link_disk_holder'
idea I posted earlier; that should take care of these issues.

It doesn't.  There is not block device you can hold, so there is no
point in claiming it.