I've done a fresh version 2.7.1 installation yesterday. I've
remembered the mail about the CONFIG_DEVTMPFS{,_MOUNT} options, so
this went well. Unfortunately, as I received the
/run/udev not writeable. Falling back to /etc/.udev.
warning, I did create this directory -- no good idea.
Hazel Russman provided the solution on linuxforums.org -- thanks.
Another point. If you put these flags in your kernel you
will get an error message next time you boot: /run/udev not
writable. Falling back to /dev/.udev. This doesn't do any
harm. Don't, whatever you do, create a /run/udev because those
who have done it lost control of their input devices. I think
this gets cleared up when you upgrade udev.