On 11-11-02 14:32, Lennart Poettering wrote:
What we do right now is this:
kill_all_processes();
do {
umount_all_file_systems_we_can();
read_only_mount_all_remaining_file_systems();
} while (we_had_some_success_with_that());
jump_into_initrd();
As long as mdmon references a file from the root disk we cannot umount
it, so the loop wouldn't be effective.
I've peeked into systemd, and from what I can see, it /only/ jumps back
to initramfs (prepare_new_root() and pivot_to_new_root()) if shutdown
"binary" is present on initramfs. And whenever mdmon is still running or
not, is not in any way determinent for pivot_root(2) call to succeed (or
... ?).
If /run/initramfs/shutdown is not present, then systemd just do the
things the old way as far as I can see - it doesn't even attempt to
pivot. And if it doesn't, the it can't umount the root (being itself
tied to it) ?
So essentially, if systemd execs /shutdown (after pivoting to
/run/initramfs) - then it's dracut's modules.d/99shutdown, which itself
sources hooks from other modules to do the rest of cleaning job. And
that should take care of all the remaining stuff (including terminating
mdmon in graceful way, and then umounting /oldroot). Either way - pretty
simple to add the necessary functionality to dracut.
So wouldn't simply a systemd's cgroup named say - immortals - with mdmon
(by default) in it suffice ? Pivot back as usual, leave mdmon alive, let
the dracut (or anything else used for initramfs) do the rest of the job
(properly).
p.s.
Sorry if I missed something obvious, it was a quick and late peek over
systemd's shutdown.c.
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