RFR: JDK-8260966 (fs) Consolidate Linux and macOS implementations of UserDefinedFileAttributeView [v3]

[Alan Bateman]

On Tue, 2 Mar 2021 05:40:05 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.
>
> Sebastian Stenzel has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Moved method below constructor and changed comment style

Thanks for the update.
A minor nit is that the new javadoc for isExtendedAttributesEnabled means there is 100+ line in the source file, mildly annoying when reviewing diffs in side-by-side view.

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Marked as reviewed by alanb (Reviewer).

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