[jdk8u-dev] RFR: 8197408: Bad pointer comparison and small cleanup in os_linux.cpp [v2]

[Jonathan Dowland]

> This is a backport of [JDK-8197408](https://bugs.openjdk.org/browse/JDK-8197408) to jdk8u-dev as part of cgroups v2. I've backported it as a pre-requisite for 8278951: containers/cgroup/PlainRead.java fails on Ubuntu 21.10 (<https://github.com/openjdk/jdk8u-dev/pull/155>)
> 
> Most of the original patch has been integrated already: I've left a whitespace change in for os_linux.cpp to hopefully avoid context problems later on. The majority of this patch is introducing the test PlainRead.java.
> 
> Not clean: test adjustments to jtreg metadata, imports, and JVM flags needed.

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 11 additional commits since the last revision:

 - 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.
 - 8244500: jtreg test error in test/hotspot/jtreg/containers/docker/TestMemoryAwareness.java
   
   When the kernel doesn't support swap limits, expect host values instead.
   
   Reviewed-by: sgehwolf
   Backport-of: fb5132254d834ba01a4b65ce64143843e83c674e
 - Update file path in comment
 - ... and 1 more: https://git.openjdk.org/jdk8u-dev/compare/3ef0d0e0...74d73c96

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

Changes:
  - all: https://git.openjdk.org/jdk8u-dev/pull/164/files
  - new: https://git.openjdk.org/jdk8u-dev/pull/164/files/3ef0d0e0..74d73c96

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=164&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=164&range=00-01

  Stats: 71 lines in 4 files changed: 50 ins; 4 del; 17 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/164.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/164/head:pull/164

PR: https://git.openjdk.org/jdk8u-dev/pull/164