On Thu, Jul 25, 2019 at 11:53:20AM -0600, Logan Gunthorpe wrote: > > > On 2019-07-25 11:40 a.m., Greg Kroah-Hartman wrote: > > On Thu, Jul 25, 2019 at 11:23:21AM -0600, Logan Gunthorpe wrote: > >> cdev_get_by_path() attempts to retrieve a struct cdev from > >> a path name. It is analagous to blkdev_get_by_path(). > >> > >> This will be necessary to create a nvme_ctrl_get_by_path()to > >> support NVMe-OF passthru. > > > > Ick, why? Why would a cdev have a "pathname"? > > So we can go from "/dev/nvme0" (which points to a char device) to its > struct cdev and eventually it's struct nvme_ctrl. Doing it this way also > allows supporting symlinks that might be created by udev rules. > > This is very similar to blkdev_get_by_path() that lets regular NVMe-OF > obtain the struct block_device from a path. > > I didn't think this would be all that controversial. > > > What is "NVMe-OF passthru"? Why does a char device node have anything > > to do with NVMe? > > NVME-OF passthru is support for NVME over fabrics to directly target a > regular NVMe controller and thus export an entire NVMe device to a > remote system. We need to be able to tell the kernel which controller to > use and IMO a path to the device file is the best way as it allows us to > support symlinks created by udev. open() in userspace handles symlinks just fine, what crazy interface passes a string to try to find a char device node that is not open()? And why do you need a char device at all anyway? Is this just the "normal" nvme controller's character device node? > > We have way too many ways to abuse cdevs today, my long-term-wish has > > always been to clean this interface up to make it more sane and unified, > > and get rid of the "outliers" (all created at the time for a good > > reason, that's not the problem.) But to add "just one more" seems > > really odd to me. > > Well it doesn't seem all that much like an outlier to me. Everyone is special, just like everyone else :) Seriously, as no one else has ever needed this, you are an outlier. thanks, greg k-h
