[crac] RFR: 8351701: [CRaC] CRaCEngineOptions=help cannot be used with CRaCRestoreFrom [v2]

[Radim Vansa]

On Wed, 12 Mar 2025 06:35:25 GMT, Timofei Pushkin <tpushkin at openjdk.org> wrote:

>> `help` will be treated as just another engine options and passed through to the engine, which in case of crexec will lead to `crexec: unknown configure option: help` error. Using `-XX:CRaCEngineOptions=help,args=--arg` or `-XX:CRaCEngineOptions=help=true` will do the same. Both on checkpoint and on restore. There were tests for this but I removed most of them as excessive, brought them back now.
>> 
>> This is intentional, I made it this way for simplicity: would need to parse options and compare all their names to `help` otherwise — and I don't think it would bring much UX benefit. By saying "use '-XX:CRaCEngineOptions=help' to ..." in the VM option docs I meant exactly that: that "help" should be specified as the only option — this can be stated more explicitly but that would be more wordy and I think it is understandable enough as is.
>
> We can replace the above with a separate `-XX:CRaCPrintEngineHelpAndExit` VM option if the behavior above seems too unintuitive

I am fine with the existing state, was just wondering whether it will both print help and error, or just error out somewhere else... Looks like there won't be a surprise so all's good.

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PR Review Comment: https://git.openjdk.org/crac/pull/211#discussion_r1991197903