udev and 2005.0

gian · Apprentice Joined: 26 Jul 2004 Posts: 212 Location: Europe

since 2005.0 (but it might be I set some USE flag I did not set before)
emerge world -pv
would emerge udev... does that mean that amd64 is doing the transition from devfs to udev ??
(I've noted that even just
emerge gnome -pv
would emerge udev (and this is a bit surprising to me... what does udev have to do with gnome ??)

barum87 · n00b Joined: 28 Mar 2005 Posts: 62

I thought 2005.0 included udev by default
I think under kernel 2.6, devfs is deprecated.

gian · Apprentice Joined: 26 Jul 2004 Posts: 212 Location: Europe

I also thought so (that devfs was deprecated), but when I installed 2004.3 and followed as any "Good Newbye" should the handbook, it told me to install devfs or die !

Obviously I'm totally clueless regarding udev ...

zaai · Apprentice Joined: 24 Jul 2004 Posts: 175

You're both right.
'devfs' is deprecated in kernel 2.6 and udev is recommended. Both still work though and gentoo 2004.3 had devfs enabled by default. Gentoo 2005.0 has udev enabled, although it still saves the /dev tree.

Simply put, devfs and udev create the device nodes under /dev. These nodes provide access to your devices (hardware and software). The node number map to the same number as found in 'cat /proc/devices'. The role of devfs and udev is to create a /dev/<node> when the device is detected by hotplug, and remove it when it is disabled.
The difference between the two is that udev works in user space and devfs operates in the kernel. udev has several advantages because of this. For more information see the references below.

I've been using a pure udev system on amd64 for a year now and it works like a charm.
- disabled devfs in the kernel
- emerge udev
- unmerge devfs
- disabled device tarball (RC_DEVICE_TARBALL="no" in /etc/conf.d/rc)
You need to be careful with the last step, if you're not sure leave it set to yes.
The nice thing of setting this to no is that you will only see detected devices under /dev
However, this also means that if a device has no rules defined it won't show and you'll have to create the device node manually.

One example of a missing device node is /dev/ppp. The workaround is to put
"mknod -m 660 /dev/ppp c 108 0" in /etc/conf.d/local.start
This creates a character device with major number 108 and minor number 0.
Where does 108 come from? "cat /proc/devices" shows you the list of character and block devices, and 108 is ppp.

More information can be found here:
http://www.gentoo.org/doc/en/udev-guide.xml
http://webpages.charter.net/decibelshelp/LinuxHelp_UDEVPrimer.html
http://ftp.kernel.org/pub/linux/utils/kernel/hotplug/udev-FAQ
_________________
* most bugs can be reduced to either dependency or state *

Athlon64 X2 4800+ on Asus M2N SLI deluxe with 4GB Dual channel
video nVidia GForce 7300 GS 512MB (snail); xorg-7.2
kernel 2.6.24-gentoo-r3

gian · Apprentice Joined: 26 Jul 2004 Posts: 212 Location: Europe

WOW ! thanks, clear as glass !

(should I also unset the devfs flag in /etc/conf.d/rc just below the tarball one ?)

dragonian · n00b Joined: 22 Feb 2005 Posts: 41

I still can't get udev to work. Something about my combination is not good. I've followed a couple of things that are supposed to work, and still i get segfaults boot.

I have not gotten udev to work. I don't know if it's genkernel or lvm, or ?? but it segfaults, and I can't access my root device.

So I use devfs, and it works fine, I haven't tried it in a week or so, since it's rather painfull.

zaai · Apprentice Joined: 24 Jul 2004 Posts: 175

Do you look here?
If you use genkernel then take a look at Hint 2.
Otherwise you need to provide more information as to what steps you take and what your kernel configuration is.
_________________
* most bugs can be reduced to either dependency or state *

Athlon64 X2 4800+ on Asus M2N SLI deluxe with 4GB Dual channel
video nVidia GForce 7300 GS 512MB (snail); xorg-7.2
kernel 2.6.24-gentoo-r3

dragonian · n00b Joined: 22 Feb 2005 Posts: 41