On Tue, Mar 13, 2012 at 4:20 PM, Alan Mackenzie <a...@muc.de> wrote: > 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.
IMHO, the thing that most people are missing is the fact that neither udev nor Linux "got complicated". The computing world itself "got complicated". We have Linux running in the same beige machines it has been running since 1991, but it also runs in TVs, tablets, cellphones, fridges, cars, ebook readers, and (soon enough, I'm sure) the kitchen sink. This devices behave very differently from our old and beloved beige boxen. They need to handle lots of different hardware comming and going, via USB, Firewire, Bluetooth, WIMAX, and who knows what else in the future. The principal idea behind udev, is that we *don't* kown (we *can't* know) what hardware this or that machine is gonna have at some point. And we want the machine (and the new hardware) to "just work" when they are connected. This is overkill for our old and beloved beige boxen? In some cases; not in mine, where I have bluetooth headphones, cell phones, and gamepads, and USB speakers, or where I connect different LCD/LED TVs to my machines. But for some very specific cases it is overkill, in the sense that fuel injection is "overkill" to get a car moving. And the guys pushing this changes believe that we don't need to cater to the simple beige box (usually servers) crowd anymore: we already got them. We need to cater to everybody else: in particular, at this moment (if the analysts numbers are right) the users of Linux in cellphones surpases the users of Linux in beige boxen... and by a lot it seems. We need to focus in them, and hope they will ask for Linux in their beige boxen if they like their other gadgets. We can discuss the merits of their plan, but I for one I'm with them. I've been using Linux more than 15 years, and with my GNOME 3 system today (yes, with udev, and systemd, and PulseAudio) I'm much more productive than with the command line 10 years ago. My servers run systemd; they not need it, in the sense that they could work without it (and my car run without fuel injection). But I'm very happy with the features running systemd in a server gives me (and the fuel efficiency the fuel injection gives my car). So, yeah, it's more complicated. The world got complicate; better get used to it. Regards. -- Canek Peláez Valdés Posgrado en Ciencia e Ingeniería de la Computación Universidad Nacional Autónoma de México
