[jdk8u-dev] RFR: 8278951: containers/cgroup/PlainRead.java fails on Ubuntu 21.10 [v3]

[Jonathan Dowland]

> This is a backport of 8278951 to jdk8u-dev as part of the cgroups v2 backport initiative.
> 
> Dependent PRs are in use.
> 
> It was clean (modulo path shuffles). The use of `log_trace` needed adjusting for jdk8u-dev.

Jonathan Dowland has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:

 - replace log_trace with tty->print_cr
 - 8278951: containers/cgroup/PlainRead.java fails on Ubuntu 21.10
   
   Reviewed-by: sgehwolf
   Backport-of: 35172cdaf38d83cd3ed57a5436bf985dde2d802b
 - PlainRead: ProcessBuilder: jdk8u-appropriate command line flags
 - adjust jtreg settings and imports for 8u
 - 8197408: Bad pointer comparison and small cleanup in os_linux.cpp
   
   Reviewed-by: bobv, stuefe
 - Test fix by Severin. Thanks!
 - replace post-jdk8u Optional.isEmpty
 - 8239559: Cgroups: Incorrect detection logic on some systems
   
   Adjust heuristic with cgroup mounts according to mountinfo
   
   Backport-of: 53ee0c4963007b86db7979312b81f990e6ce271a
 - 8240189: [TESTBUG] Some cgroup tests are failing after JDK-8231111
   
   Reviewed-by: mdoerr
   Backport-of: c92adf41587767e9c5c8e116cfaeb375d36928aa
 - Don't pass --add-exports to jdk8u java inside docker
   
   These are JDK9+ module specific parameters.
 - ... and 3 more: https://git.openjdk.org/jdk8u-dev/compare/e6c38804...7fc8633b

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

Changes:
  - all: https://git.openjdk.org/jdk8u-dev/pull/155/files
  - new: https://git.openjdk.org/jdk8u-dev/pull/155/files/e6c38804..7fc8633b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=155&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=155&range=01-02

  Stats: 71 lines in 4 files changed: 50 ins; 4 del; 17 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/155.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/155/head:pull/155

PR: https://git.openjdk.org/jdk8u-dev/pull/155