An example mdev.conf

Thu Nov 5 21:11:26 UTC 2009

On Thursday 05 November 2009 11:19:31 Natanael Copa wrote:
> On Thu, 2009-11-05 at 01:52 -0600, Rob Landley wrote:
> > So solar at gentoo has maintained his own mdev.conf for a while:
> >
> >   ftp://tinderbox.x86.dev.gentoo.org/misc/mdev.conf
> >
> > And Cross Linux From Scratch picked up a variant of it:
> >
> >   http://cross-lfs.org/view/clfs-embedded/x86/bootscripts/mdev.html
> >
> > It would be nice if busybox had an example mdev.conf in the examples
> > directory, and these seem to be the main ones being used in the field.
>
> Have a look at this one too:
> http://git.alpinelinux.org/cgit/aports/tree/main/busybox-initscripts/mdev.c
>onf

Yay, more to pile on!

Possibly we want 2 examples mdev.conf files.  One really tiny one that just 
changes the permissions on /dev/null and /dev/zero and such so a non-root 
process can at least _run_, and a second "kitchen sink" version containing 
everything we know about.

>#
># This is a sample mdev.conf.
>#
>
># Devices:
># Syntax: %s %d:%d %s
># devices user:group mode
>
># null does already exist; therefore ownership has to be changed with
> command null	root:root 0666	@chmod 666 $MDEV
>zero	root:root 0666

Should mdev grow a more graceful way to do that?  (This is a design question, 
and if I start making design decisions for mdev I'm going to go back in and 
RIP OUT the stupid "individually re-malloc and free every single line of the 
file over and over for every device mdev -s handles and then do it again when 
responding to hotplug events" code, and put back the faster/smaller/simpler 
mmap version back in.  If you want to genericize the mmap version, fine.  But 
unnecessarily doing 8 gazillion small malloc/frees is painful even when you're 
not trying to support nommu...)

Anyway, I'm wild guessing that "mdev -s" should stomp existing permissions (at 
least when we actually have a mdev.conf line for it instead of just a default 
value), but hotplug shouldn't?

>zero	root:root 0666

0:0 is smaller than root:root, and won't change.

Also, failure to look up a numeric uid/gid in /etc/passwd shouldn't really be 
an error.  We know how to handle it, and people who grab our default config file 
won't necessarily grab a default passwd and group from us.  (In this case, 
what they probably really care about is that this device has a _unique_ 
owner/group, which they can attach to later if they care.)

>grsec	root:root 0660

This is the default value, there's no reason to specify it that I'm aware of.

># console does already exist; therefore ownership has to be changed with
> command console	root:tty 0600	@chmod 600 $MDEV && mkdir -p vc && ln -sf
> 	../$MDEV vc/0 fd0	root:floppy 0660

Same as the earlier comment about changing mdev behavior to set permissions 
automatically, plus I believe there's a symlink syntax already you should be 
able to use for this?

I admit to being somewhat out of the loop with the symlink syntax.  Solar 
designed that, and I forget quite how it works.

By the way, what actually needs the vc/0 crud, anyway?  Didn't devfs names die 
with devfs?  (And /dev/console _isn't_ a virtual console, it could be a serial 
device.)

>kmem	root:root 0640
>mem	root:root 0640
>port	root:root 0640
>ptmx	root:tty 0666
>
># ram.*
>ram([0-9]*)	root:disk 0660 >rd/%1
>loop([0-9]+)	root:disk 0660 >loop/%1
>sd[a-z].*	root:disk 0660 */lib/mdev/usbdisk_link
>hd[a-z][0-9]*	root:disk 0660 */lib/mdev/ide_links
>md[0-9]		root:disk 0660

Ooh, there _is_ a regex syntax for parentheticals.  (I am so out of the loop.  
And I need to update mdev.txt it seems.)

And while I'm at it, the symlink syntax solar and LFS are using doesn't match 
what mdev.txt documents.  I wonder if they're patching mdev?

>tty		root:tty 0666
>tty[0-9]	root:root 0600
>tty[0-9][0-9]	root:tty 0660

Presumably tty[0-9]* would handle all of those cases?

Why is the middle of the three different than the first and last?

>ttyS[0-9]*	root:uucp 0660
>pty.*		root:tty 0660
>vcs[0-9]*	root:tty 0660
>vcsa[0-9]*	root:tty 0660
>
>
>ttyLTM[0-9]	root:dialout 0660 @ln -sf $MDEV modem
>ttySHSF[0-9]	root:dialout 0660 @ln -sf $MDEV modem
>slamr		root:dialout 0660 @ln -sf $MDEV slamr0
>slusb		root:dialout 0660 @ln -sf $MDEV slusb0
>fuse		root:root  0666
>
># dri device
>card[0-9]	root:video 0660 =dri/
>
># alsa sound devices and audio stuff
>pcm.*		root:audio 0660	=snd/
>control.*	root:audio 0660	=snd/
>midi.*		root:audio 0660	=snd/
>seq		root:audio 0660	=snd/
>timer		root:audio 0660	=snd/

Isn't there some kind of curly bracket syntax we can feed to these regexes to 
group essentially identical lines like this?  (This is actually a regex 
question, not an mdev question.)

Who created the "snd" directory, anyway?  (Your init scripts before calling 
mdev?)

>adsp		root:audio 0660 >sound/
>audio		root:audio 0660 >sound/
>dsp		root:audio 0660 >sound/
>mixer		root:audio 0660 >sound/
>sequencer.*	root:audio 0660 >sound/
>
># misc stuff
>agpgart		root:root 0660  >misc/
>psaux		root:root 0660  >misc/
>rtc		root:root 0664  >misc/
>
># input stuff
>event[0-9]+	root:root 0640 =input/
>mice		root:root 0640 =input/
>mouse[0-9]	root:root 0640 =input/
>ts[0-9]		root:root 0600 =input/
>
># v4l stuff
>vbi[0-9]	root:video 0660 >v4l/
>video[0-9]	root:video 0660 >v4l/
>
># dvb stuff
>dvb.*		root:video 0660 */lib/mdev/dvbdev
>
># load drivers for usb devices
>usbdev[0-9].[0-9]	root:root 0660 */lib/mdev/usbdev
>usbdev[0-9].[0-9]_.*	root:root 0660
>
># net devices
>tun[0-9]*	root:root 0600 =net/
>tap[0-9]*	root:root 0600 =net/
>
># zaptel devices
>zap(.*)		root:dialout 0660 =zap/%1
>dahdi!(.*)	root:dialout 0660 =dahdi/%1
>
># raid controllers
>cciss!(.*)	root:disk 0660 =cciss/%1
>ida!(.*)	root:disk 0660 =ida/%1
>rd!(.*)		root:disk 0660 =rd/%1

Quite a long config file.

>sr[0-9]		root:cdrom 0660 @ln -sf $MDEV cdrom

Um, why don't the = and > options work here?

(And when we _unplug_ devices, do those symlinks get properly removed?  Or the 
moved device nodes?)

> -nc

Rob
-- 
Latency is more important than throughput. It's that simple. - Linus Torvalds