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

[Bernd]

On Wed, 2 Apr 2025 18:39:57 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 hard-coded to `lib/tzdb.dat` and `lib/security/cacerts`. Only those two files from the `java.base` module will be allowed to be upgraded with a link from the current run-time image.
> 2. The upgrade needs to be opt-in. Similar to `--ignore-signing-information` for signed modular JARs. A user needs to add `--upgrade-files=<module>/<file-path>` for it to succeed.
> 
> `--upgrade-files` is a hidden `jlink` option since it only does anything for JEP 493 enabled builds. Users get a hint to apply the option if they so desire:
> 
> Example:
> 
> 
> $ ./bin/jlink --add-modules java.base --output java.base-jdk
> Error: [..]/lib/security/cacerts has been modified
> Hint: lib/security/cacerts is an upgradeable file. Add --upgrade-files=java.base/lib/security/cacerts to allow the upgrade.
> 
> 
> using the hint we get:
> 
> 
> $ ./bin/jlink --add-modules java.base --output java.base-jdk --upgrade-files=java.base/lib/security/cacerts
> $ ./java.base-jdk/bin/java --list-modules
> java.base at 25-internal
> $ sha512sum ./java.base-jdk/lib/security/cacerts 
> cf2b4c17161e79001c8e07def3de36c0d523f00a2a6b6e33893a2a3669d930957c11ac765dd29d5ff80e63ad100ef0258291891377f7133b997111ba97b15146  ./java.base-jdk/lib/security/cacerts
> $ sha512sum ./lib/security/cacerts 
> cf2b4c17161e79001c8e07def3de36c0d523f00a2a6b6e33893a2a3669d930957c11ac765dd29d5ff80e63ad100ef0258291891377f7133b997111ba97b15146  ./lib/security/cacerts
> 
> 
> **Testing**
> 
> - [ ] GHA
> - [x] `jdk/tools/jlink` jtreg tests
> - [x] Some manual tests with updated `tzdb.dat` and `cacerts` files.
> 
> Thoughts?

Well, shipping customized runtimes sounds like a valid usecase, but yes maybe it’s more important for jpackage.

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PR Comment: https://git.openjdk.org/jdk/pull/24388#issuecomment-2774651205