RFR: 8302744: Refactor Hotspot container detection code

[Severin Gehwolf]

On Mon, 6 May 2024 16:51:33 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Please review this container detection code refactoring in hotspot. The main point of this is to
>> 
>> - get rid of the `GET_CONTAINER_INFO` macros which hide too many things under the hood
>> - prevent refactoring of the code (since `GET_CONTAINER_INFO` macros short-return and are therefore not portable; at least not without some risk)
>> - make the code easier to understand
>> - allow for better testing via `gtest`
>> - separate multi-line parsing from single line parsing for clarity.
>> 
>> Testing:
>> - [x] GHA
>> - [x] `gtest:cgroupTest` tests
>> - [x] Container tests on Linux with cgroup v1 (legacy) and cgroup v2. All pass.
>> 
>> Thoughts?
>
> src/hotspot/os/linux/cgroupSubsystem_linux.hpp line 87:
> 
>> 85:     return OSCONTAINER_ERROR;
>> 86:   }
>> 87: 
> 
> We can simplify this coding by just using fscanf. No need to call fgets + sscanf.

I was taking the advise of the `scanf` man page here:

       The  scanf()  family  of functions scans input like sscanf(3), but read
       from a FILE.  It is very difficult to use  these  functions  correctly,
       and  it  is preferable to read entire lines with fgets(3) or getline(3)
       and parse them later with sscanf(3) or more specialized functions  such
       as strtol(3).

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

PR Review Comment: https://git.openjdk.org/jdk/pull/19060#discussion_r1592122105