provide handover interface to host

[lnussel]

There are use cases where scripts inside a transaction need to convey information back to the host such as openSUSE/sdbootutil#92. So far scripts try to abuse /dev/shm due to lack of a better solution.

Therefore I'd like to propose to introduce e.g. /run/transactional-update/snapshot/$id that is then bind mounted as /run of snapshot $id while it's open.

[lnussel]

Another option would be to provide something like /run/host like systemd-nspawn: https://systemd.io/CONTAINER_INTERFACE/

That one would still require special treatment inside the transaction though while the bind mount solution could just transparently see stuff that existing packages touch in /run anyway.

[aplanas]

I am testing now a plugin mechanism for tukit, that it is executed while the chroot environment is alive (but not active). The plugins can use the host /run to transfer this information and drop /dev/shm. Can be an alternative to this proposal, as can be extended by different projects that provider their own plugins (sdbootutil, suse-module-tools, t-u, etc)

[aplanas]

Proposal: #122

[laenion]

#122 was merged. It may still be worth thinking about a dedicated handover interface, so I'm leaving this ticket open for now.