Re: Basic rundown of udev?

[Kay Sievers]

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

Udev stuff is usually handled at linux-hotplug@xxxxxxxxxxxxxxxx

> Anyone care to give me a brief map? ÂIt would help. ÂI'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? ÂAnd 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
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