Re: [gentoo-user] Beta test Gentoo with mdev instead of udev; version 5 - failure :-(

[Alan Mackenzie]

Hello, Neil.

On Tue, Mar 13, 2012 at 09:33:30PM +0000, Neil Bothwick wrote:
> On Tue, 13 Mar 2012 21:07:37 +0000, Alan Mackenzie wrote:

> > But I really meant what functionality udev has that mdev lacks.  For
> > example, mdev this morning recognised my USB stick being inserted, and
> > created /dev/sdc for it.

> udev does a *lot* more than that, for example the persistent naming of
> network interfaces. More significantly, it can run programs based on
> device rules.

This is where I start getting unhappy.  Is there any need for this
blurring?  Having device nodes is essential to a linux system, and
some programs use these nodes.  Why must they be mashed together into a
tasteless mush?  Is there some advantage to this I haven't twigged yet?

> For example, usb_modeswitch installs a udev rule to switch a 3G USB
> modem from CD to modem mode, without which it won't work.

Same question as above: why does that switching have to be done via the
device node system rather than via the driver.  Isn't that what drivers
are for?

> That's fine when you plug it into a running system, but when you boot
> with it plugged in, it can trip over itself because the usb_modeswitch
> executable is in /usr/sbin.

Er, that's a different discussion altogether.  ;-)

> You could use this to argue that /usr should be mounted before udev is
> started, but you could just as well use it to argue that udev should not
> be trying to run such rules at the boot runlevel.

Or that udev shouldn't have "rules".  I still don't understand the basic
concept driving this thing.  My HDDs don't need rules - they just need a
mapping from /dev/sd[ab] into device 8/0 and 8/16, and the appropriate
drivers built into my kernel.

Am I being stupid?  Despite your example above, I still don't see what
udev is about, why it's necessary, or even why it's advantageous.

> --
> Neil Bothwick

-- 
Alan Mackenzie (Nuremberg, Germany).