[crac] RFR: 8353243: [CRaC] Show all options in engine help [v4]

[Radim Vansa]

On Tue, 8 Apr 2025 10:53:21 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 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 four additional commits since the last revision:
> 
>  - Make list of VM-controlled options static
>  - Use comma as a separator when printing controlled options
>  - Simplify vm_controlled_options
>  - Show all options in engine help

Marked as reviewed by rvansa (Committer).

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PR Review: https://git.openjdk.org/crac/pull/220#pullrequestreview-2749785631