RFR: JDK-8262957 (fs) Fail fast in UnixFileStore.isExtendedAttributesEnabled

[Sebastian Stenzel]

On Thu, 4 Mar 2021 02:10:57 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Added new capability flag `UnixNativeDispatcher.SUPPORTS_XATTR`, which gets set `#ifdef _SYS_XATTR_H_`.
>> 
>> Note that `_SYS_XATTR_H_` is defined in `xattr.h` in both [macOS/Darwin](https://github.com/apple/darwin-xnu/blob/main/bsd/sys/xattr.h), [Linux and GNU-based BSD systems using glibc](https://github.com/bminor/glibc/blob/master/misc/sys/xattr.h). It might not be defined for other operating systems that still support xattr. So if OpenJDK eventually adds support for further platforms, this might need to be adjusted as well.
>> 
>> If xattr capabilities are missing, `UnixFileStore.isExtendedAttributesEnabled` will return false immediately, avoiding any I/O.
>> 
>> As a side effect of this change, I redefined some other (private) capabilities. Strictly speaking, this change is not required but keeps the code consistent, as [previously discussed in the mailing list](https://mail.openjdk.java.net/pipermail/nio-dev/2021-February/008133.html).
>
> I think this look all right. I'll withhold approving until @AlanBateman has commented.

@bplb @AlanBateman Bump ��

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PR: https://git.openjdk.java.net/jdk/pull/2816