At 2014/6/14 22:36, Greg KH wrote:
On Sat, Jun 14, 2014 at 10:58:53AM +0800, Simon Guo wrote:
Forward to USB mail alias for the USB question.
-------- Original post -------- Subject: Question about USB hotplug Date: Sat, 14 Jun 2014 09:59:45 +0800 Sender: Simon Guo <wei.guo.simon@gmail.com> Receiver: kernelnewbies@kernelnewbies.org, wei.guo.simon@gmail.com
Hi, dear list,
I want to be clear about the USB hotplug procedure.
I read "Linux Device Driver" and "Documentation/usb/hotplug.txt", and google much. Per my understanding, the USB hotplug works as following: 1) Insertion of physical U-disk will trigger a hardware interrupt. And interrupt handler (installed by USB bus driver?) will create kobj at /sys. 2) According to Linux device model, the creation of kobj will raise hotplug event (implemented in USB bus driver). 3) user space hotplug helper is invoked to handle hotplug event. Hotplug helper will read "modules.usbmaps" and decide to load which USB driver. If there are many drivers matching the device, they will all be loaded? 4) udev will create approparite dev under /dev according to rules defined. Please correct me if I am wrong in the above.
I am using Ubuntu 11, and with my own build kernel version 3.15.0.
Please ask on a Ubuntu mailing list, they are the only distro that people have problems with this, so they must be doing something "odd" compared to everyone else.
Thanks Greg. The feedback from Ubuntu list indicates udev(which was developed by you) is used to handle hotplug, and the procedure I listed was out-of-date. Whereas "Documentation/usb/hotplug.txt" doesn't mention udev at all. BR, Simon