Users can specify an artifact cache quota larger than their disk size

Summary

Users can specify an artifact cache quota larger than their disk size. This makes no sense.

Steps to reproduce

Set

cache:
  quota: *value > current disk space*

in ~/.config/buildstream.conf. Now build a system larger than the remaining disk space.

What is the current bug behavior?

Builds will be allowed to run despite running out of disk space.

What is the expected correct behavior?

Buildstream should tell me that my quota is too large and do something that isn't building as if I had a much larger disk than I have.

Possible fixes

While parsing somewhere around here, we should check if the disk quota exceeds the amount of drive space available.

If you're feeling particularly fancy, you can make buildstream figure out how much space its cache uses, then figure out how full the drive is, and then check if quota > remaining + cache. If not, simply checking if quota > disk space might be enough.

Other relevant information

• BuildStream version affected: /milestone %"BuildStream_v1.3"

---