Skip using the active slot as a seed when installing bundles

[fhackenberger]

As a workaround for resource intensive and slow install procedures when using casync and tar images (see #511) I created an option for the install command, which skips using the active slot as a seed when running casync.

This enables the following use case:

• Remote repository chunk store contains only chunks for most recent update
• Images have a .caexclude file included, which prevents /var/tmp/update.casync.castr from being chunked
• Device does the bind-mount & casync make --store /var/tmp/update.casync.castr /var/tmp/update.casync.caidx /mnt/rauc/ step in the background once.
• Device does an rsync with --delete on remote chunks store / index file / raucb
• Device installs without using slot as seed rauc install --ignore-seed bundle.raucb

The workaround decribed splits the long running operations into separate units, which can be run independently and frees the device to do a full casync make on every update. Downside is that additional storage is used permanently. But that's probably good, as it makes it clear how much space is actually left, if updates should still work.

[codecov]

Codecov Report

Merging #513 into master will decrease coverage by 0.02%.
The diff coverage is 27.27%.

@@            Coverage Diff             @@
##           master     #513      +/-   ##
==========================================
- Coverage    66.5%   66.47%   -0.03%     
==========================================
  Files          24       24              
  Lines        6463     6470       +7     
==========================================
+ Hits         4298     4301       +3     
- Misses       2165     2169       +4

Impacted Files	Coverage Δ
src/main.c	67.43% <0%> (-0.06%)	⬇️
src/update_handler.c	37.05% <0%> (-0.1%)	⬇️
src/service.c	75.27% <100%> (+0.09%)	⬆️
src/install.c	80.7% <66.66%> (-0.08%)	⬇️

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[fhackenberger]

I'm not really familiar with your testing requirements. Can someone else contribute a test for this new feature?

[fhackenberger]

@ejoerns How do you feel about the tests? Would you or someone else be able to add them? I've looked at the testing code, but I'm quite unfamiliar with the framework.

[ejoerns]

I agree that it is a use case to disable seeding. Mainly because of casync's limited capabilities in seed store cleanup and for devices with really constrained temporary storage.

Thus basically introducing an option to disable seeding is something that I'd like to see.

But the way for selecting this option you chose is probably the wrong one:

• You break the API of the Install D-Bus command which will prevent all current API users from simply updating to a new RAUC release
• Deciding to not use the slot as a seed store is probably not a property of an installation but instead a property of the system.

To target the first point, we have #446 hanging around and waiting for getting merged.
But because of the second point I would prefer having a simple system config option that allows disabling seeding.

I thought that we already had some own developments towards this direction, but I was not able to find any.

@OnkelUlla could you also please have a look at this as you just cared for the casync stuff in context of #501 ?

[fhackenberger]

Thanks for the feedback @ejoerns! I agree it should rather be a system setting in system.conf, having it as an argument for the install command is less than ideal. Not sure if I have the time to adapt this soon, so I'd also be happy if someone else continues this work.