RFR: 8353185: Introduce the concept of upgradeable files in context of JEP 493 [v4]

[Alan Bateman]

On Mon, 7 Apr 2025 13:35:57 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> For JEP 493-enabled builds there are no JMODs. Certain files come from the installed JDK image when a user creates a custom run-time from it. This is problematic for example for files that often come from a different package (e.g. `cacerts` file for Linux distro builds of OpenJDK packaged as RPMs), or more generally when they get updated out-of-band of the JDK build itself like the tzupdater tool.
>> 
>> When that happens the hash sum recorded at JDK build time of those files no longer match, causing `jlink` to fail. I propose to allow for those files to get "upgraded" should this happen. The way this works is as follows:
>> 
>> 1. The list of upgradeable files is configured by a resource file in `jdk.jlink` on a per module basis. Right now, only two files from the `java.base` module will be allowed to be upgraded with a link from the current run-time image.
>> 2. For those files the hash sum checks are skipped.
>> 
>> **Testing**
>> 
>> - [x] GHA
>> - [x] `jdk/tools/jlink` jtreg tests (also on [GHA](https://github.com/jerboaa/jdk/actions/runs/14308729271))
>> - [x] Some manual tests with updated `tzdb.dat` and `cacerts` files.
>> 
>> Thoughts?
>
> Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review v2

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/LinkableRuntimeImage.java line 71:

> 69:     private static InputStream getDiffInputStream(String module) throws IOException {
> 70:         String resourceName = String.format(DIFF_PATTERN, module);
> 71:         return JDK_JLINK_MOD.getResourceAsStream(resourceName);

FYI you can use LinkableRuntimeImage.class.getResourceAsStream here as the resource is in the current module.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24388#discussion_r2031696600