RFR: JDK-8264111 (fs) Leaking NativeBuffers in case of errors during UnixUserDefinedFileAttributeView.read/write [v3]

[Sebastian Stenzel]

> Added new private methods for `read(String name, long address, int rem)` and `write(String name, long address, int rem)` that take an address as an argument and thereby no longer need to deal with any NativeBuffers.
> 
> This allows a certain simplification of `read(String name, ByteBuffer dst)` and `write(String name, ByteBuffer src)` and use of `try (NativeBuffer nb = NativeBuffers.getNativeBuffer(rem)) {...}` which fixes the issue.

Sebastian Stenzel has updated the pull request incrementally with one additional commit since the last revision:

  Added reachabilityFence when dealing with DirectBuffer

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3171/files
  - new: https://git.openjdk.java.net/jdk/pull/3171/files/d3cb759b..2f1f2132

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3171&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3171&range=01-02

  Stats: 16 lines in 1 file changed: 8 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3171.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3171/head:pull/3171

PR: https://git.openjdk.java.net/jdk/pull/3171