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? Thanks, Daniel _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
