The prior use of the UID is uninteresting in general for consumers who
wants to learn things about _what_ the build is, not what is the UID of
the build user running it.
Achieving this with a place where a mapping between cgroup names and
build requests are maintained is non trivial because there's no "global"
daemon that keeps track of this information and such a daemon would
require a persistent location to track this.
Rather than solving that, we will just encode the derivation hash inside
the cgroup name. Userspace can simply pull this apart and query Nix to
obtain the original corresponding derivation for more information.
This provides userspace with a way to map cgroup names to pnames for
example. Going further, if you have a map between attribute paths and
derivation hashes, you can power a database of cgroup metrics per
attribute paths by combining all of that.
In addition to this rename, we adopt a systemd-ish convention for
template units (`@`).
As a result, userspace tooling that will scrape cgroup metrics will
discover a consistent path as long as they filter out the UID part,
especially in context of Id6c458aad30eaa08c3609ac8280a7dde8e8f3cf9
change.
This problem is tracked under #1073.
Change-Id: I238d0568a3e4b1ff3057781c0639528d666b4d37
Signed-off-by: Raito Bezarius <raito@lix.systems>
Raito Bezarius
63871751ce