From mboxrd@z Thu Jan  1 00:00:00 1970
From: greg@kroah.com (Greg KH)
Date: Sat, 14 Jun 2014 07:36:22 -0700
Subject: Fwd: Question about USB hotplug
In-Reply-To: <539BBA6D.7030206@gmail.com>
References: <539BAC91.7070708@gmail.com>
 <539BBA6D.7030206@gmail.com>
Message-ID: <20140614143622.GB20718@kroah.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

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 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.

sorry,

greg k-h