'Twas brillig, and Daniel Drake at 11/04/12 17:33 did gyre and gimble: > On Wed, Apr 11, 2012 at 9:40 AM, Lennart Poettering > <lenn...@poettering.net> wrote: >> So on shutdown after stopping all services we execute systemd-shutdown >> as PID 1 replacing the normal systemd process. This is useful to drop >> all references to files on disk, so that we can remount the disk r/o >> even on upgrades. >> >> systemd-shutdown is basically a single loop that tries to >> umount/read-only mount all file systems it finds as long as this changes >> the list of active mounts. This code also disables all swaps and detachs >> DM/loop devices in the same loop. > > Thanks as always for the fast and good explanation! With that pointer, > I found the problem, see below. > >>> We do have a bit of a strange fs-layout, where our root fs is kept >>> inside /versions/pristine/X on the root partition. The initramfs takes >>> care of this with some bind-mount and chroot tricks so that it looks >>> 'normal' afterwards, but maybe something along these lines is >>> confusing systemd. >> >> chroot()? Meh, you should not use chroot for these kinds of things... > > Actually, we don't use chroot directly. Here's what happens: > > dracut mounts the root fs at /sysroot, then in a pre-pivot dracut > trigger OLPC does: > > mkdir /vsysroot > mount --bind /sysroot/versions/run/6 /vsysroot > umount /sysroot > NEWROOT=/vsysroot > > Dracut then goes ahead and performs switch_root on $NEWROOT to pivot > onto the real system. > > (Happy to hear advice on a nicer way to do this) > > When the system finishes booting, /proc/self/mountinfo looks like: > http://dev.laptop.org/~dsd/20120411/mountinfo.txt > > Now, in systemd-shutdown we reach mount_points_list_get() in umount.c, > which does: > > /* If we encounter a bind mount, don't try to remount > * the source dir too early */ > skip_ro = !streq(root, "/"); > > Hence skip_ro gets set to 1 for our / > > mount_points_list_remount_read_only() then ignores the / mount and > leaves it as RW during shutdown. > > I don't really understand the reasoning for the above behaviour of > bind mounts. Would it be acceptable to special-case this condition if > the path in question is / so that skip_ro does not get set? Or are > there other options available?
Keep in mind that systemd cannot umount / (and often cannot unmount /usr either) so after it has done everything it can it should re-enter the dracut initrd to let it do some additional tidy up, i.e. properly unmounting /usr and /, deactivating LVM+crypt if they were used for / or /usr (tho' I do not think either of these is done just yet - needs work at dracut side) etc. Make sure you build dracut with --systemdsystemunitdir arguement to get the dracut-shutdown.service files built and make sure they are included on the running system. HTHs Col -- Colin Guthrie gmane(at)colin.guthr.ie http://colin.guthr.ie/ Day Job: Tribalogic Limited http://www.tribalogic.net/ Open Source: Mageia Contributor http://www.mageia.org/ PulseAudio Hacker http://www.pulseaudio.org/ Trac Hacker http://trac.edgewall.org/ _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
