[crac] RFR: Support extra criu flags from the environment

[Anton Kozlov]

On Wed, 29 Jun 2022 13:00:59 GMT, Volker Simonis <simonis at openjdk.org> wrote:

> When testing with different `criu` versions or `criu` configurations it might be useful to be able to modify the default  `criu` command line parameters. This PR introduces the new environment variable `CRAC_CRIU_OPTS` which will be interpreted as a space separated list of `criu` flags to be appended to the hard-coded list of command line parameters. E.g.
> 
> 
> $ CRAC_CRIU_OPTS="-v4 -o resume.log -W /tmp/crac" java -XX:CRaCRestoreFrom=/tmp/crac
> 
> 
> This will set the logging level to 4 (thus overriding the hard-coded logging level of 1 for resuming), redirect the log to the file `resume.log` and change `criu`'s working directory (which will contain the log file) to `/tmp/crac`.

Changes requested by akozlov (Lead).

src/java.base/unix/native/criuengine/criuengine.c line 116:

> 114:         }
> 115:         *arg++ = NULL;
> 116:         assert(ARRAY_SIZE(args) >= (size_t)(arg - args));

I'm not sure if we are compiling with asserts. Could you turn this and another assert below into a runtime check and explicit failure if arguments do not fit?

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PR: https://git.openjdk.org/crac/pull/26