Re: [gentoo-user] Semi OT: hotplug / coldplug / udev ...

["Boyd Stephen Smith Jr." <bss03@volumehost.net>]

On Thursday 09 November 2006 10:01, Arnau Bria <arnau@emergetux.net> wrote 
about '[gentoo-user] Semi OT: hotplug / coldplug / udev ...':
> I have some doubts about the way hotplug / coldplug / udev work.
>
> What really happen when you plug a (again,
> i.e.) pendrive in your computer? Which programs take care in that
> process? What about kernel?

Here's my understanding, I'm sure others will correct me, and possibly 
exapnd on it:

First, there's either a HW interrupt or the kernel scans the bus and sees a 
new device.  Then, the kernel queries the device and populates /sys (and 
possibly /proc) and notifies udev. udev is responsible for loading the 
appropriate module, if not already loaded, and creating the device nodes.

In the past, hotplug and coldplug where responsible for loading the module, 
and devfs would create device nodes under control of the module.  Neither 
hotplug nor coldplug are required with recent udev (w/ module loading 
support).  Hotplug and/or coldplug can provide module loading for early 
versions of udev (in addition to their role with devfs).

In ancient times, device nodes had to be created by the user (static /dev), 
possibly in response to kernel events (put that would require a module for 
the kernel hooks) or en masse for all possible devices.  One 
(dis?)advantage to static /dev was that device nodes would persist across 
reboots, which does not happen under devfs or udev -- unless your distro. 
provided /dev tarballs (ala Gentoo) or another method to save /dev on 
shutdown and restore it on startup.

-- 
"If there's one thing we've established over the years,
it's that the vast majority of our users don't have the slightest
clue what's best for them in terms of package stability."
-- Gentoo Developer Ciaran McCreesh
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