Fwd: Question about USB hotplug

[Simon Guo]

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 at gmail.com>
>> Receiver: kernelnewbies at kernelnewbies.org, wei.guo.simon at 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was out-of-date.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