On Thu, 30 Aug 2018, Faisal Mehmood wrote: > Based on my (limited) understanding if I were to disable udev, the > userspace should not be able to enumerate/interact with any newly > connected device since udev handles uevents generated by kernel. > (right?) That's not quite right. Yes, udev does handle uevents. But a newly connected device may be usable from userspace, to some extent, without any handling of uevents. > So as a test, I disabled systemd-udevd and then plugged in a flash > drive. I disabled support for usb mass storage in the kernel. So 'lsblk' > didn't show the device, just as expected. However, 'lsusb' still > dynamically updates the list as I repeatedly plugin and remove a flash > drive. An example of what I described above. > Then I studied libusb/lsusb code for a bit. It seems that lsusb makes use > of 'libusb_get_device_list()' to find the connected usb devices. But I > couldn't find any detail regarding implementation of > libusb_get_device_list. That's an internal aspect of libusb, so it might not be described in the documentation. You can always check the source code if you really want to know how it works. I think it may look at the files under /sys/bus/usb/devices/ -- that's certainly one possibility which would always work even without udev. > I am sure I'm missing something. Could someone please help me understand > what is happening behind the scenes? udev does things like loading drivers into the kernel (modprobe'ing them) and creating nodes under /dev. But a driver that is already present in the kernel doesn't need to be modprobe'd, and the files under /sys are created automatically by the kernel rather than by udev. Does that answer your questions? Alan Stern
