Re: [PATCH 00/19] nvme: switch to libmultipath

[John Garry <john.g.garry@oracle.com>]

On 02/03/2026 14:12, Christoph Hellwig wrote:
> On Wed, Feb 25, 2026 at 03:39:48PM +0000, John Garry wrote:
>> This switches the NVMe host driver to use libmultipath. That library
>> is very heavily based on the NVMe multipath code, so the change over
>> should hopefully be straightforward. There is often a direct replacement
>> for functions.
> 
> Given how little code this removes while adding the new libmultipath
> dependency and abstractions I can't say I like this at all.
> 

Yeah, so we're losing about 300 lines here in the conversion. However 
nvme mulitpath.c goes from 1410 -> 1250 lines with this series - that's 
not good enough to justify the change.

In a quick review of the code, there is more stuff which I push down 
(into the lib). And a lot of the abstraction code can be condensed - if 
you check something like numa_node_show(), there are 6 variables needed 
just to get to the point where the common helper could be called - that 
is just silly.

Another issue is just that the remaining code is NVMe specific, like ANA 
support, or just doesn't fit the SCSI model, e.g. NVMe iopolicy is per 
subsystem, while for SCSI we don't have a subsystem concept and I so 
made iopolicy per multipathed SCSI disk.