On Wed, Dec 06, 2017 at 07:26:13PM +0100, Krzysztof Opasiak wrote: > > > On 12/06/2017 07:26 AM, Greg KH wrote: > > On Tue, Dec 05, 2017 at 10:09:35PM +0000, andy_purcell@xxxxxxxxxxxx wrote: > > > I have implemented a USB device using functionfs. > > > A colleague now says our app must run as a normal user, not as root. > > > > > > I tried it and it does not work. > > > The problem is this - the endpoint files created by the OS are owned by root. > > > These ep files are created after I write the descriptors and strings to the /dev/usbffs/ep0 file. > > > > > > $ ls -l /dev/usbffs/ > > > total 0 > > > -rw-rw-rw- 1 xyzuser xyzgrp 0 Dec 5 21:36 ep0 > > > -rw------- 1 root root 0 Dec 5 21:39 ep1 > > > -rw------- 1 root root 0 Dec 5 21:39 ep2 > > > -rw------- 1 root root 0 Dec 5 21:39 ep3 > > > > > > A normal user-space app cannot open, write, read, these ep files. > > > > > > Is there a remedy for this? > > > > Write a udev rule to change the owners of those files :) > > > > You must have done that already for the ep0 file, right? > > > > FunctionFS is a separate file system not a group of device nodes it's just > mounted under /dev/usbffs. So technically epX are not device nodes and as > far as I know (please correct me if I'm wrong) there is no uevent then epX > is created. Ah, yeah, you are right, sorry about that, mounting filesystems at /dev/ always confuses everyone :) > Can we use udev for a custom files other than device nodes? Isn't it only > uevent parser? Yes it is, so no, it will not really work for this, sorry. > I'm not sure if you use systemd or not but there is a FunctionFS based > activation and this is how we solve this problem. systemd is running as a > root and opens all epX files and pass them to the service which then can run > with lower privileges. Additional benefit is that systemd doesn't close > those fds so even if your demon crashes whole gadget is not going away, all > other functions are still usable. Ah, nice, that should work well. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
