Hi, Some package modified my /etc/init.d/udev to need /usr/lib/systemd/systemd-udevd and system failed to boot properly as I didn't have it. I installed sys-apps/systemd which required the uninstallation of sys-fs/udev as versions later than 186 provide it and there is no flag to disable the included udev. Bad thing is that no ebuild actually checks for systemd-186 and expect sys-fs/udev. Both versions are marked unstable but not masked. A workaround is to add --nodeps at emerge command line. Thank you.
Oh, it's corrected in systemd-188 Sorry!