Question about USB hotplug

Question about USB hotplug

[Simon Guo]

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.
Currently a new plugged USB disk can be recognized by my Ubuntu.
But I didn't see "modules.usbmaps" file under /lib/modules/`uname -r`
root at thunderCat:/mnt/data# ls /lib/modules/`uname -r`
build   modules.alias      modules.builtin      modules.dep
modules.devname  modules.softdep  modules.symbols.bin
kernel  modules.alias.bin  modules.builtin.bin  modules.dep.bin
modules.order    modules.symbols  source

And there is no /proc/sys/kernel/hotplug
root at thunderCat:/mnt/data# cat /proc/sys/kernel/hotplug

root at thunderCat:/mnt/data# file /sbin/hotplug
/sbin/hotplug: ERROR: cannot open `/sbin/hotplug' (No such file or
directory)

My Question is:
1) How can my Ubuntu hotplug work without "modules.usbmaps" and
"/sbin/hotplug"?
2) Is there any tech I can use to "trace" the kernel/driver behavior of
the USB hotplug procedure? (for example, kernel functions traversed)

Thanks,
Simon



The config should have enabled HOTPLUG:


root at thunderCat:/mnt/data# grep CONFIG_HOTPLUG /boot/config-`uname -r`
CONFIG_HOTPLUG_CPU=y
CONFIG_HOTPLUG_PCI_PCIE=y
CONFIG_HOTPLUG_PCI=y
# CONFIG_HOTPLUG_PCI_COMPAQ is not set
# CONFIG_HOTPLUG_PCI_IBM is not set
# CONFIG_HOTPLUG_PCI_ACPI is not set
CONFIG_HOTPLUG_PCI_CPCI=y
# CONFIG_HOTPLUG_PCI_CPCI_ZT5550 is not set
# CONFIG_HOTPLUG_PCI_CPCI_GENERIC is not set
# CONFIG_HOTPLUG_PCI_SHPC is not set

Fwd: Question about USB hotplug

[Simon Guo]

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.
Currently a new plugged USB disk can be recognized by my Ubuntu.
But I didn't see "modules.usbmaps" file under /lib/modules/`uname -r`
root at thunderCat:/mnt/data# ls /lib/modules/`uname -r`
build   modules.alias      modules.builtin      modules.dep
modules.devname  modules.softdep  modules.symbols.bin
kernel  modules.alias.bin  modules.builtin.bin  modules.dep.bin
modules.order    modules.symbols  source

And there is no /proc/sys/kernel/hotplug
root at thunderCat:/mnt/data# cat /proc/sys/kernel/hotplug

root at thunderCat:/mnt/data# file /sbin/hotplug
/sbin/hotplug: ERROR: cannot open `/sbin/hotplug' (No such file or
directory)

My Question is:
1) How can my Ubuntu hotplug work without "modules.usbmaps" and
"/sbin/hotplug"?
2) Is there any tech I can use to "trace" the kernel/driver behavior of
the USB hotplug procedure? (for example, kernel functions traversed)

Thanks,
Simon



The config should have enabled HOTPLUG:


root at thunderCat:/mnt/data# grep CONFIG_HOTPLUG /boot/config-`uname -r`
CONFIG_HOTPLUG_CPU=y
CONFIG_HOTPLUG_PCI_PCIE=y
CONFIG_HOTPLUG_PCI=y
# CONFIG_HOTPLUG_PCI_COMPAQ is not set
# CONFIG_HOTPLUG_PCI_IBM is not set
# CONFIG_HOTPLUG_PCI_ACPI is not set
CONFIG_HOTPLUG_PCI_CPCI=y
# CONFIG_HOTPLUG_PCI_CPCI_ZT5550 is not set
# CONFIG_HOTPLUG_PCI_CPCI_GENERIC is not set
# CONFIG_HOTPLUG_PCI_SHPC is not set

Fwd: Question about USB hotplug

[Greg KH]

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

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@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