RFR: 8261242: [Linux] OSContainer::is_containerized() returns true when run outside a container

[Severin Gehwolf]

Please review this enhancement to the container detection code which allows it to figure out whether the JVM is actually running inside a container (`podman`, `docker`, `crio`), or with some other means that enforces memory/cpu limits by means of the cgroup filesystem. If neither of those conditions hold, the JVM runs in not containerized mode, addressing the issue described in the JBS tracker. For example, on my Linux system `is_containerized() == false" is being indicated with the following trace log line:


[0.001s][debug][os,container] OSContainer::init: is_containerized() = false because no cpu or memory limit is present


This state is being exposed by the Java `Metrics` API class using the new (still JDK internal) `isContainerized()` method. Example:


java -XshowSettings:system --version
Operating System Metrics:
    Provider: cgroupv1
    System not containerized.
openjdk 23-internal 2024-09-17
OpenJDK Runtime Environment (fastdebug build 23-internal-adhoc.sgehwolf.jdk-jdk)
OpenJDK 64-Bit Server VM (fastdebug build 23-internal-adhoc.sgehwolf.jdk-jdk, mixed mode, sharing)


The basic property this is being built on is the observation that the cgroup controllers typically get mounted read only into containers. Note that the current container tests assert that `OSContainer::is_containerized() == true` in various tests. Therefore, using the heuristic of "is any memory or cpu limit present" isn't sufficient. I had considered that in an earlier iteration, but many container tests failed.

Overall, I think, with this patch we improve the current situation of claiming a containerized system being present when it's actually just a regular Linux system.

Testing:

- [x] GHA (risc-v failure seems infra related)
- [x] Container tests on Linux x86_64 of cgroups v1 and cgroups v2 (including gtests)
- [x] Some manual testing using cri-o

Thoughts?

-------------

Commit messages:
 - jcheck fixes
 - Fix tests
 - Implement Metrics.isContainerized()
 - Some clean-up
 - Drop cgroups testing on plain Linux
 - Implement fall-back logic for non-ro controller mounts
 - Make find_ro static and local to compilation unit
 - 8261242: [Linux] OSContainer::is_containerized() returns true

Changes: https://git.openjdk.org/jdk/pull/18201/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18201&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8261242
  Stats: 360 lines in 20 files changed: 258 ins; 78 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/18201.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18201/head:pull/18201

PR: https://git.openjdk.org/jdk/pull/18201