[crac] RFR: 8353243: [CRaC] Show all options in engine help [v3]

[Timofei Pushkin]

On Tue, 8 Apr 2025 10:43:54 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
>
> Timofei Pushkin has refreshed the contents of this pull request, and previous commits have been removed. Incremental views are not available.

Rebased on top of the current main branch just in case (GitHub showed a conflict), no changes

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PR Comment: https://git.openjdk.org/crac/pull/220#issuecomment-2786026131