nvme_get_by_path() is analagous to blkdev_get_by_path() except it
gets a struct nvme_ctrl from the path to its char dev (/dev/nvme0).
The purpose of this function is to support NVMe-OF target passthru.
I can't find anywhere that you use this in this patchset.
Oh sorry, the commit message is out of date the function was actually
called nvme_ctrl_get_by_path() and it's used in Patch 10.
Instead of by path, could we have configfs take something else, like
the unique controller instance or serial number? I know that's different
than how we handle blocks and files, but that way nvme core can lookup
the cooresponding controller without adding new cdev dependencies.