Hi Philipp, The flow you mentioned is something which I was not aware of. I would like to see it happening in code. My Queries are as follows: 1) " The kernel then creates an uevent and notifies the userspace part of udev (udevd) through a netlink socket. " - What are the corresponding files that i need to check? If the question is too abstract, kindly explain me with respect to any sample Bus. 2) "The uevent is received by udevd and now udev can check for rules to add the device node to /dev" - Again the same thing. I would like to see it inside the code. Please help me in looking at the real code. Thanks again Philipp for your valuable answer. Regards, -Manty On Fri, Apr 20, 2012 at 7:24 PM, Philipp Ittershagen < p.ittershagen@googlemail.com> wrote:

Hi Manty!

On Fri, Apr 20, 2012 at 3:29 PM, manty kuma <mantykuma@gmail.com> wrote:

...

Hi,

I want to know how a node is created when a hardware is connected to the system.

Information that I know : When a hardware is connected to the system, the device name is compared with the driver name, if it matches, then probe is called.

Info i wish to know: At which point is the node created and who is creating it(In other words, i want to know where is mknod happening)?

This one thing is bugging my mind from so many months. Please tell me programatically where is this happening. I will be very thankful.

Please correct me if I'm wrong, my understanding is this:

The hardware is connected and the corresponding subsystem or bus will be notified (i.e. by interrupt of the device). The kernel then creates an uevent and notifies the userspace part of udev (udevd) through a netlink socket. The uevent is received by udevd and now udev can check for rules to add the device node to /dev. That's when the creation and naming of the device node happens.

Greetings,

Philipp

On Fri, Apr 20, 2012 at 4:04 PM, manty kuma <mantykuma@gmail.com> wrote:

Hi Philipp,

The flow you mentioned is something which I was not aware of. I would like to see it happening in code.

My Queries are as follows:

1) " The kernel then creates an uevent and notifies the userspace part of udev (udevd) through a netlink socket. " -  What are the corresponding files that i need to check? If the question is too abstract, kindly explain me with respect to any sample Bus.

The article at http://www.linuxjournal.com/article/8093 explains the initialization mechanism for USB. I don't have any code experience on USB hubs but by following the functions mentioned in the article (expecially the khubd kthread) you can see that the interrupt I mentioned is handled by the USB subsystem. Next, the uevent is created. The generic(?) implementation of this can be found at http://lxr.free-electrons.com/source/drivers/usb/core/driver.c#L722, where you can see that the uevent contains the necessary data for creating a udev entry. By sending the uevent we're crossing the kernel/userspace boundary and you have to take a look at the udev and udevd implementation for more information.

2)  "The uevent is received by udevd and now udev can check for rules to add the device node to /dev" - Again the same thing. I would like to see it inside the code. Please help me in looking at the real code.

If a `man udev` does not answer your questions, you should take a look at the source code at http://git.kernel.org/?p=linux/hotplug/udev.git;a=summary. Again, please correct me if I'm wrong :) Hope this helps, Philipp