Relevant Gentoo news article

file_463475.txt (text/plain), 1.51 KB, created by Vasyl Tretiakov on 2013-03-27 13:00:45 UTC

2013-01-23-udev-upgrade
  Title                     Upgrading udev from 171 (or older) to 197 (or
                            newer)
  Author                    Samuli Suominen <[e-mail]>
  Posted                    2013-01-23
  Revision                  1

Upgrading udev from 171 (or older) to 197 (or newer) will require special attention:

- Remove udev-postmount from runlevels.

- The need of CONFIG_DEVTMPFS=y in the kernel; need to verify the fstype for
  possible /dev line in /etc/fstab is devtmpfs (and not, for example, tmpfs)

- The case of predictable network interface names; if the file
  /etc/udev/rules.d/70-persistent-net.rules is being used for renaming
  network interface names to already existing names, then you need to
  read following bug[1] because it's no longer possible. This won't
  be a problem with the new predictable network interface name scheme[2].

  [1] http://bugs.gentoo.org/453494
  [2] http://www.freedesktop.org/wiki/Software/systemd/
      PredictableNetworkInterfaceNames

- The case of separate /usr; if it worked for you with 171 it will continue
  to work for you with 197 (or newer). We still recommend initramfs with separate
  /usr mounting capabilities because you might need packages like sys-apps/kbd
  (keymaps in /usr) or net-wireless/bluez (possible keyboard) in early boot.

And read every message printed by the emerge of udev and udev-init-scripts
to ensure the system is in order before booting as this news item might
not be complete.