[PATCH] nvme-multipath: add an 'ana_groups_only' module option

[Sagi Grimberg]

> On large installations the ANA log buffer can be exceedingly large;
> we've come across a controller with 49 ANA Group Descriptors and
> 65536 namespaces, resulting in an ANA buffer with an order-7 allocation.
> And this is just to validate that the namespace ID is _really_listed
> in the log page.
> So to avoid an overly large memory allocation we can leverage the
> 'RGO' bit when retrieving the ANA log page, and check whether the
> ANA group ID from the namespace is found in the ANA descriptors.
> That cuts down the memory allocation, and provides the same result.
> But to be on the safe side I've added a module option 'ana_groups_only'
> to switch between modes.

Hannes, why not a sysfs writable attribute? One can add a udev rule if
it wants a one-shot all controllers...

Although maybe that will bring us to yet another attribute that is
unstable until the controller identifies...

I think we are getting more indication that the controller device
creation is sitting in the wrong place...