Node creation For real time devices

Philipp Ittershagen p.ittershagen at
Fri Apr 20 10:42:28 EDT 2012

On Fri, Apr 20, 2012 at 4:04 PM, manty kuma <mantykuma at> 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 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,
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

> 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;a=summary.

Again, please correct me if I'm wrong :)

Hope this helps,


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