RFR: 8349988: Change cgroup version detection logic to not depend on /proc/cgroups [v2]

[Thomas Fitzsimmons]

> This pull request fixes https://bugs.openjdk.org/browse/JDK-8349988 and https://bugs.openjdk.org/browse/JDK-8347811.
> 
> I tested it with:
> 
> 
> java -Xlog:os+container=trace -version
> 
> on:
> 
> `Red Hat Enterprise Linux 8 (cgroups v1 only)`:
> _No change in behaviour_
> 
> `Fedora 41 (cgroups v2)`:
> _More verbose output due to `/sys/fs/cgroup/cgroup.controllers` parsing:_
> 
> --- tt-old-f41.txt	2025-02-26 15:37:56.310738515 -0500
> +++ tt-new-f41.txt	2025-02-26 15:37:56.601739407 -0500
> @@ -1,7 +1,12 @@
>  [trace][os,container] OSContainer::init: Initializing Container Support
> -[debug][os,container] Detected optional pids controller entry in /proc/cgroups
> -[debug][os,container] controller cpuset is not enabled
> -                    ] 
> +[debug][os,container] v2 controller cpuset is enabled and relevant
> +[debug][os,container] v2 controller cpu is enabled and required
> +[debug][os,container] v2 controller io is enabled but not relevant
> +[debug][os,container] v2 controller memory is enabled and required
> +[debug][os,container] v2 controller hugetlb is enabled but not relevant
> +[debug][os,container] v2 controller pids is enabled and relevant
> +[debug][os,container] v2 controller rdma is enabled but not relevant
> +[debug][os,container] v2 controller misc is enabled but not relevant
>  [debug][os,container] Detected cgroups v2 unified hierarchy
>  [trace][os,container] Adjusting controller path for memory: /sys/fs/cgroup/user.slice/user-4215196.slice/user at 4215196.service/app.slice/app-org.gnome.Terminal.slice/vte-spawn-135086d6-2de4-4f2e-ad94-899b5eecaf83.scope
>  [trace][os,container] Path to /memory.max is /sys/fs/cgroup/user.slice/user-4215196.slice/user at 4215196.service/app.slice/app-org.gnome.Terminal.slice/vte-spawn-135086d6-2de4-4f2e-ad94-899b5eecaf83.scope/memory.max
> 
> 
> `Fedora 41 (custom kernel with cgroups v1 disabled)`:
> _Fixes `cgroups v2` detection:_
> 
> --- tt-old-f41-custom-kernel.txt	2025-02-26 15:37:58.197744304 -0500
> +++ tt-new-f41-custom-kernel.txt	2025-02-26 15:37:59.380747933 -0500
> @@ -1,7 +1,63 @@
>  [trace][os,container] OSContainer::init: Initializing Container Support
> -[debug][os,container] Detected optional pids controller entry in /proc/cgroups
> -[debug][os,container] controller cpuset is not enabled
> -                    ] 
> -[debug][os,container] controller memory is not enabled
> -                    ] 
> -[debug][os,container] One or more required controllers disabled at kernel level.
> +[debug][os,container] v2 controller cpuset is enabled and relevant
> +[debug][os,container] v2 contro...

Thomas Fitzsimmons has updated the pull request incrementally with 10 additional commits since the last revision:

 - Detect cpuset-disabled condition during cgroups v1 /proc/cgroups parsing
   
   Remove from cgroups v1 branch incorrect log messages about cpuset
   controller being optional.  Add test case for cgroups v1, cpuset
   disabled.
 - Improve !cgroups_v2_enabled branch comment
 - Debug-log optional and disabled cgroups v2 controllers
   
   Do not log enabled controllers that are not relevant to the JDK.
 - Move index declaration to scope in which it is used
 - Remove empty string check during cgroup.controllers parsing
 - Define ISSPACE_CHARS macro, use it in strsep call
 - Pass fgets result to strsep
 - Replace is_cgroupsV2 with cgroups_v2_enabled
   
   Also fix the testCgroupv1SystemdOnly and testCgroupv1NoMounts test
   cases such that their /proc/cgroups and /proc/self/cgroup contents
   correspond.  This prevents assertion failures these tests were
   producing when is_cgroupsV2 was replaced with cgroups_v2_enabled.
 - Comment statfs check
 - Add redefinition guard for CGROUP2_SUPER_MAGIC

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23811/files
  - new: https://git.openjdk.org/jdk/pull/23811/files/39a6463c..67107287

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23811&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23811&range=00-01

  Stats: 127 lines in 2 files changed: 92 ins; 13 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/23811.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23811/head:pull/23811

PR: https://git.openjdk.org/jdk/pull/23811