Node creation For real time devices

[Philipp Ittershagen]

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