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https://github.com/cgwalters/atomic-pkglayer

Demo of package layering
https://github.com/cgwalters/atomic-pkglayer

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Demo of package layering

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This patchset has moved
-----------------------

See https://github.com/projectatomic/rpm-ostree/pull/107

Layering RPM packages on top of an (rpm-)ostree tree
----------------------------------------------------

This is a proof-of-concept for RPM package layering on top of an
OSTree base tree. It is only a demonstrator; do not use in
production.

To use:

# ./atomic-pkglayer add strace

Now, let's try:

# ostree admin status

What's up with that ? Well, OSTree is telling us
it no longer knows how to upgrade the system. If you look at the
origin file underneath `/ostree/deploy/.../*.origin` for the new
deployment, you'll see that we have listed the additional packages,
and the refspec is now `base_refspec`.

And indeed if we try it:

# atomic upgrade
error: No origin/refspec in current deployment origin; cannot upgrade via ostree

Anyways, let's reboot, and notice that strace is available.

# systemctl reboot
# rpm -q strace

A very important thing to note; we do have a single unified RPM
database, still in /usr/share/rpm.

Upgrading
---------

# ./atomic-pkglayer upgrade

This will check for *both* tree upgrades and new packages. Oh, and it
will redownload the packages every time. Because, again, this is just
a proof of concept...

Removing layered packages
-------------------------

# ./atomic-pkglayer remove strace

Unlike most package systems, this can *only* be used to remove
explicitly added packages. It's not allowed to remove packages from
the base tree, nor packages that are intermediate dependencies of
added packages.

Integrating this into rpm-ostree
--------------------------------

There are a number of reasons I wrote this proof-of-concept as an
addon layer.

* The whole subject deserves a lot of thought and careful coding,
and ultimately will require changes in RPM to make this work more
widely.
* There's a strong drive right now to backport rpm-ostree to EL7,
and that limits the dependency/feature growth.
* For rpm-ostree, we intend to use the new C libraries of hawkey/librepo
for package management - this will allow much tighter integeration
than using yum allows.
* yum is GPL, rpm-ostree is LGPL (for several reasons, but an important one
is to allow ASL2.0 code to link to it)