RFR: JDK-8260966 (fs) Consolidate Linux and macOS implementations of UserDefinedFileAttributeView

[Alan Bateman]

On Wed, 17 Feb 2021 08:41:43 GMT, Sebastian Stenzel <github.com+1204330+overheadhunter at openjdk.org> wrote:

> Deduplicated code in these classes:
> - `LinuxUserDefinedAttributeView` + `BsdUserDefinedAttributeView` → `UnixUserDefinedAttributeView`. Due to different supported length of attribute names, I added an abstract method `UnixUserDefinedAttributeView.maxNameLength()`.
> - `LinuxNativeDispatcher` + `BsdNativeDispatcher` → `UnixNativeDispatcher`. I basically just moved the Linux implementation up to Unix and added preprocessor directives to distinguish Linux/BSD/Other. Others will throw ENOTSUP UnixExceptions.
> - `LinuxFileStore.isExtendedAttributesEnabled()` + `BsdFileStore.isExtendedAttributesEnabled()` → `UnixFileStore.isExtendedAttributesEnabled()`
> 
> For the latter I introduced `UnixConstants.XATTR_NOT_FOUND`, which is `ENODATA` on Linux and `ENOATTR` on BSD. Note that `UnixConstants.ENODATA` is still present, as @AlanBateman "would prefer if we left ENODATA so that it can be used in Linux specific code" (Quote from https://github.com/openjdk/jdk/pull/2363#issuecomment-772534587)
> 
> This also fixes `Files.copy(src, dst, StandardCopyOption.COPY_ATTRIBUTES)` on macOS/BSD. Previosly an [invocation was missing](https://github.com/openjdk/jdk/blob/jdk-17%2B7/src/java.base/macosx/classes/sun/nio/fs/BsdFileSystem.java#L70-L72).
> 
> I plan to add further commits to clean up this code, once the deduplication is reviewed.

Thanks for spitting up the steps in the refactoring as it makes it easier to review. One other thing that is still creating noise in the patch is that I think your IDE or editor has changed the formatting to 8 space indent in several places where the original code in LinuxUserDefinedFileAttributeView.java was 4 space indent. We've typically used 4 space indent in this code. If you revert those indentations then I think it will reduce the size of the patch and make it easy for us to see where the real changes are.

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PR: https://git.openjdk.java.net/jdk/pull/2604