Basic rundown of udev?

Basic rundown of udev?

[John Moser]

I'm currently reading through umm... udevd.c for udev-141.  Trying to
figure out how this thing works.

Anyone care to give me a brief map?  It would help.  I'm just trying
to figure out how udev talks to the kernel-- i.e. what facilities
would I have to implement to re-implement the kernel side of udev,
let's say if I was to run udevd as-is on Darwin or NetBSD or
something.  How does it talk to the kernel?  And if you know off the
top of your head, which source files (and functions?) am I looking at
here?

Re: Basic rundown of udev?

[Kay Sievers]

On Thu, Apr 16, 2009 at 22:39, John Moser <john.r.moser@gmail.com> wrote:
> I'm currently reading through umm... udevd.c for udev-141.  Trying to
> figure out how this thing works.

Udev stuff is usually handled at linux-hotplug@vger.kernel.org.

> Anyone care to give me a brief map?  It would help.  I'm just trying
> to figure out how udev talks to the kernel

Udev just listens to broadcasted events from the kernel.

Just run:
  udevadm monitor --kernel --env
and
  strace udevadm monitor --kernel
and you see what's going on.

> -- i.e. will what facilities
> would I have to implement to re-implement the kernel side of udev,
> let's say if I was to run udevd as-is on Darwin or NetBSD or
> something.

Udev uses the Linux kernel device tree exported by sysfs. It offers
simplified access to the internal device structures in the kernel. Not
sure what other platforms do here.

> How does it talk to the kernel?  And if you know off the
> top of your head, which source files (and functions?) am I looking at
> here?

The kernel sends the needed events from: lib/kobject_uevent.c, but
that does not include the driver core, which is in drivers/base/*, and
the exported device tree filesystem at fs/sysfs/*.

Good luck,
Kay