Messages in this thread | | | From | Logan Gunthorpe <> | Date | Thu, 25 Jul 2019 11:53:20 -0600 | Subject | Re: [PATCH v6 02/16] chardev: introduce cdev_get_by_path() |
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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.
> 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.
Logan
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