On Wed, Oct 26, 2011 at 5:57 AM, clemens fischer <ino-news@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Thomas Bächler wrote: > >> Am 25.10.2011 20:12, schrieb clemens fischer: >> >>>> Mounting /usr needs to go to the initramfs. It is possible to >>>> implement a mount handler for this. At this stage, the by-label >>>> symlinks exist already. >>> >>> AFAIU udevd(8) is responsible for setting up those symlinks. How can >>> they exist _before_ udevd(8) is started? >> >> I'll let you go back and read everything again, what you are saying >> makes no sense whatsoever, and I have no idea how to reply to it. > > Lucky you, I have a way to explain it: There are udev rules referencing > stuff in /usr. If people mount /usr by-label or by-uuid, udev must have > completed to setup those symlinks. Catch-22. most of the time initramfs install scripts will inject everything you need, even if stuff is in /usr, just fine, and it will all work correctly ... in initramfs. udev has everything it needs to run properly in that environment (once the real init takes over these assurances *POOF*) ... keep in mind udev will actually be ran twice, the first being killed off before real init exec's and takes over. the reasons for not supporting separate /usr are very similar to the reasons for not supporting /run and /run/lock on within var anymore -- define "system binary". the answer is transient, subjective, and contextual -- my system is not your system is not their system -- eg, systemd needs udev at step ONE ... nobody would have guessed init would dep dbus 5+ years ago (except the visionaries of course ;-). separate usr is mostly pointless in my experience, though there are probably several appropriate niche cases. per your "udev references /usr", if you look at the rule, it tries /sbin and /usr/sbin -- in that order -- and it just so happens that: # which dmsetup /sbin/dmsetup udev doesnt do much beyond actually creating the symlinks, the UUIDs/LABELs -> blockdev mappings are discovered by blkid (take a look at the rules). like most things "*nix-ey", udevd is more-or-less a dumb shell that provides a convenient environment for *other* tools to do the heavy lifting. it's "personal" task is to create nodes with proper permissions + names + links as the kernel finds them ... that's about it. Tom/Thomas, I would be interested in experimenting with this as time allows. I'm not sure i grasp the problem though ... after switch_root and mount --move why can't initiscripts or systemd simply notice the mount and tear it down? i must be overlooking something critical because it's like 4am, but this seems related to a problem ive been having w/systemd (on GPT -> MDRAID -> LVM2 ->EXT4) where at the last second systemd flashing a message about not being about to deactivate one device (the root?, i have swap/boot/root all on that array) -- C Anthony
