[systemd-devel] 'Offline System Updates' examination

[Alexander E. Patrakov]

2012/6/21 Lennart Poettering <lennart at poettering.net>:
> On Wed, 20.06.12 22:23, Antonio Trande (anto.trande at gmail.com) wrote:
>
>> 'Offline System Updates' will come as feature for Fedora 18. Reading your
>> official page <http://freedesktop.org/wiki/Software/systemd/SystemUpdates>:
>>
>> The system update script now creates a btrfs snapshot (if possible), then
>> > installs all RPMs. After completion (regardless whether the update
>> > succeeded or failed) the /system-update symlink is removed. In addition, on
>> > failure it reverts to the old btrfs state (modulo the aforementioned
>> > symlink), on success it leaves the newly made changes in place.
>> >
>>
>> BTRFS ? Will 'Offline Updates' be available only with BTRFS ?
>
> Nope. But on btrfs we'll make a snapshot of the old system state. On
> non-btrfs we won't.

As far as I understand from the design document, both on btrfs and on
ext4 the sequence is:

1) Download updates
2) Reboot into a minimal environment (system-update.target), make a
snapshot if the FS supports it
3) Install updates automatically
4) Reboot

And I have two questions about that:

1) Can one configure the system to use kexec instead of the reboot?
(BTW, the only machine that I have access to and where kexec doesn't
work is a multi-CPU KVM guest)

2) Did anyone consider a plan to do updates on ext4 and btrfs
differently? E.g. one can use the same sequence as above for ext4 and
"make a writable snapshot, install to snapshot, reboot with that
snapshot as root" on btrfs. This, theoretically, has a huge advantage
of being able to work on on source-based distributions like gentoo
(unlike the original sequence, which means at least 1 hour of complete
downtime due to compilation of LibreOffice at step 3).

-- 
Alexander E. Patrakov