From mboxrd@z Thu Jan 1 00:00:00 1970 From: gregkh@linuxfoundation.org (Greg Kroah-Hartman) Date: Thu, 25 Jul 2019 21:34:15 +0200 Subject: [PATCH v6 02/16] chardev: introduce cdev_get_by_path() In-Reply-To: <5951e0f5-cc90-f3de-0083-088fecfd43bb@grimberg.me> References: <20190725172335.6825-1-logang@deltatee.com> <20190725172335.6825-3-logang@deltatee.com> <20190725174032.GA27818@kroah.com> <682ff89f-04e0-7a94-5aeb-895ac65ee7c9@deltatee.com> <20190725180816.GA32305@kroah.com> <20190725182701.GA11547@kroah.com> <5951e0f5-cc90-f3de-0083-088fecfd43bb@grimberg.me> Message-ID: <20190725193415.GA12117@kroah.com> On Thu, Jul 25, 2019@12:02:30PM -0700, Sagi Grimberg wrote: > > > > > > Why do you have a "string" within the kernel and are not using the > > > > > normal open() call from userspace on the character device node on the > > > > > filesystem in your namespace/mount/whatever? > > > > > > > > NVMe-OF is configured using configfs. The target is specified by the > > > > user writing a path to a configfs attribute. This is the way it works > > > > today but with blkdev_get_by_path()[1]. For the passthru code, we need > > > > to get a nvme_ctrl instead of a block_device, but the principal is the same. > > > > > > Why isn't a fd being passed in there instead of a random string? > > > > I wouldn't know the answer to this but I assume because once we decided > > to use configfs, there was no way for the user to pass the kernel an fd. > > That's definitely not changing. But this is not different than how we > use the block device or file configuration, this just happen to need the > nvme controller chardev now to issue I/O. So, as was kind of alluded to in another part of the thread, what are you doing about permissions? It seems that any user/group permissions are out the window when you have the kernel itself do the opening of the char device, right? Why is that ok? You can pass it _any_ character device node and away it goes? What if you give it a "wrong" one? Char devices are very different from block devices this way. thanks, greg k-h