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paulj
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PostPosted: Sun Jan 26, 2014 8:08 pm    Post subject: Gentoo on the Beaglebone without udev Reply with quote

I followed the comprehensive installation instructions to load gentoo onto my BeagleBone White. I have just been through the process of updating it to the 3.8.13 version of the kernel, so I have a consistent approach to handling GPIOs on this and my BBB (i.e. through device trees). One issue I would like to challenge now is the need to have udev on the BeagleBone. While I understand this is useful for managing hotplugging of devices through the usb, in my case this is not required. Any peripherals or devices I use are connected through GPIO pins and managed by the software without recourse to udev.

The information for Ye Olde Fashioned Gentoo is great for giving pointers to starting from scratch, but I would like to remove udev from the existing install. Have any of you been though the process of removing udev from an existing system rather than by building from scratch? If so, are there any pitfalls I need to be aware of before commencing? One of the challenges I have with this system is that it is installed on a 4GB card, and the portage tree is on a network file share, so as long as I don't lose my network access, and have access to a shell, all is not lost! I can also make a complete backup before starting, so it isn't a disaster if I fall over.

Thanks!
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NeddySeagoon
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PostPosted: Sun Jan 26, 2014 8:29 pm    Post subject: Reply with quote

paulj,

udev does little more than fix permissions on /dev entries created by the kernel DEVTMPFS.
If you don't mind /dev entries being root:root you can probably live without udev.

For every package in your world file run
Code:
equery depends udev


There are two sorts of depends, the easy one you fix by settind USE=-udev and rebuilding everthing with it -N (newuse).
That takes care of optional udev support.

It gets harder when packages IUSE +udev. That means it must be on for these packages.
Copy the ebuilds to your overlay and edit them to remove udev.

Without udev in something like Xord, evdev and auto device detection no longer works.
You will need an xorg.conf file. Effects vary. You get to keep the pieces. :)

There are also lighter solutions, like mdev.
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Computer users fall into two groups:-
those that do backups
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paulj
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PostPosted: Sun Jan 26, 2014 9:39 pm    Post subject: Reply with quote

NeddySeagoon wrote:
paulj,

udev does little more than fix permissions on /dev entries created by the kernel DEVTMPFS.
If you don't mind /dev entries being root:root you can probably live without udev.


If my understanding is correct, I could create the /dev entries by hand, and not rely on DEVTMPFS? This means I could create the correct permissions?

NeddySeagoon wrote:


For every package in your world file run
Code:
equery depends udev


There are two sorts of depends, the easy one you fix by settind USE=-udev and rebuilding everthing with it -N (newuse).
That takes care of optional udev support.

It gets harder when packages IUSE +udev. That means it must be on for these packages.
Copy the ebuilds to your overlay and edit them to remove udev.

Without udev in something like Xorg, evdev and auto device detection no longer works.
You will need an xorg.conf file. Effects vary. You get to keep the pieces. :)

There are also lighter solutions, like mdev.


I will give this a go and see what comes out. xorg and evdev etc is no issue - I don't even connect the Beaglebone to a screen or a keyboard. Access is either through ssh or via the terminal made available in the usb port. mdev might be worth considering as this would perhaps make it possible to use the USB port to hot plug should that be required. I am tempted to continue with the original objective of removing udev to see how easy (or not!) it is!
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NeddySeagoon
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PostPosted: Sun Jan 26, 2014 9:58 pm    Post subject: Reply with quote

paulj,

If you turn off DEVTMPFS, yes you can have a static /dev

Gentoo used to ship stage3 tarballs with a static /dev anyway.
The DEVTMPFS /dev was mounted over the top of the static /dev.

Have a look in /dev when the root filesystem is not live.
You will need to do all of your own module loading if you go this route.
/etc/conf.d/modules is your friend.
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Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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