Reduce the usage of JNI in the Linux attach provider by making more use of the `Path` API.
- use the `Path` API to read file permissions - use the `Path` API to write to and read from Unix domain sockets - use JDK internal APIs to access the euid and eguid After this the sole usage of JNI in the Linux attach provider will be to send a signal using `kill`. I ran the tier1 and serviceability test suites and they both pass. I verified I can attach to and attach using a locally built JDK. I didn't do any Docker related tests. I split the changes into two commits: - The first commit ports the permission check code more or less directly from C to Java using integer based checks. - The second commit changes the permission check code to use higher level Java abstractions (`UserPrincipal`, `Set`, ...) I hope this makes it easier to review and verify the changes preserve the semantics. To the best of my knowledge `uid_t` is an unsigned 32 bit integer. `VM#geteuid()` returns it as `long`, unsigned. However `UnixUserPrincipals#fromUid` expects an `int`, I believe casting is the correct way to convert in this case. I tried to keep unrelated changes to `VirtualMachineImpl` to a minimum. I did however replace all usages of `java.io.File` with `java.nio.file.Path` and made two methods `static`. We could get rid of the `socket_path` instance variable if we instead use `socket_address` to flag a disconnect. Ultimately the same changes can be applied to the macOS an AIX implementations. ------------- Commit messages: - 8364281: Reduce JNI usage in Linux attach provider - 8364281: Reduce JNI usage in Linux attach provider Changes: https://git.openjdk.org/jdk/pull/26712/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26712&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8364281 Stats: 337 lines in 3 files changed: 45 ins; 242 del; 50 mod Patch: https://git.openjdk.org/jdk/pull/26712.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/26712/head:pull/26712 PR: https://git.openjdk.org/jdk/pull/26712
