Re: update mechanism for new releases
The main point, where olpc-update wins without a shadow of a doubt,
is
failure-friendliness. Assuming a fail-safe filesystem, olpc-update can
be interrupted (hard) at any point, might take N runs to complete. And
will only switch to the 'new' image once it's completed in an atomic
operation.
RPM is unfortunately a disaster in this space. If an rpm transaction
fails, there are no sane ways to recover it. On XO-1 a full OS update
transaction with rpm will take a very long time, so it's highly
likely that it will be interrupted. RPM and yum hackers treat this as
an intractable problem.
Have you tried the « yum-complete-transaction » tool ? It comes from
the yum-utils package and might interest you :)
This is, IMO, the actual showstopper. If we had a fs that could
handle
snapshotting, then we could snapshot the system before starting the
RPM transaction, and have recovery hooks in the boot partition or in
initrd. There's been discussion on fedora-devel about hooking up yum
with btrfs transactions
I probably am way over my knowledge, but what about LVM snapshots ?
- olpc-update offers downgrades, but our software at higher layers
doesn't support this. The Journal format upgrade broke downgrades in
the last OS upgrade. Sugar 0.84 has another Journal format change,
probably with a similar upgrade-only path.
Yum/RPM also have downgrades. See the « yum-allow-downgrade » plugin
and the « --oldpackage » RPM option.
I'm don't know if those cover all the use cases you might have for
downgrades though.
----------
Mathieu Bridon (bochecha)