[crac] RFR: 8353243: [CRaC] Show all options in engine help

[duke]

On Mon, 31 Mar 2025 08:58:32 GMT, Timofei Pushkin <tpushkin at openjdk.org> wrote:

> C/R engines are now advised to list all options in `configuration_doc`. If JVM does not let users to control some options it states that in the engine help message.
> 
> crexec now documents internal options, such as `image_location` and `exec_location`, in its doc message.
> 
> This is how crexec's help looks with this change:
> 
> $ java -XX:CRaCEngineOptions=help
> crexec - pseudo-CRaC-engine used to relay data from JVM to a "real" engine implemented as an executable (instead of a library). The engine executable is expected to have CRaC-CRIU-like CLI. Support of the configuration options also depends on the engine executable.
> 
> Configuration options:
> * image_location=<path> (no default) - path to a directory with checkpoint/restore files.
> * exec_location=<path> (no default) - path to the engine executable.
> * keep_running=<true/false> (default: false) - keep the process running after the checkpoint or kill it.
> * direct_map=<true/false> (default: true) - on restore, map process data directly from saved files. This may speedup the restore but the resulting process will not be the same as before the checkpoint.
> * args=<string> (default: "") - free space-separated arguments passed directly to the engine executable, e.g. "--arg1 --arg2 --arg3".
> 
> Configuration options controlled by the JVM: image_location exec_location

@TimPushkin 
Your change (at version 71c4227fb5575cb47f07572d30adb4a26ea0b3f9) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/crac/pull/220#issuecomment-2766018546