File system notifications for Go Files

This version of fsnotify needs Go 1.16 (this was already the case since 1.5.1, but not documented). It also increases the minimum Linux version to 2.6.32.

Additions

• all: add Event.Has() and Op.Has() (#477)

This makes checking events a lot easier; for example:

    if event.Op&Write == Write && !(event.Op&Remove == Remove) {
    }

Becomes:

    if event.Has(Write) && !event.Has(Remove) {
    }

• all: add cmd/fsnotify (#463)

A command-line utility for testing and some examples.

Changes and fixes

• inotify: don't ignore events for files that don't exist (#260, #470)

Previously the inotify watcher would call os.Lstat() to check if a file still exists before emitting events.

This was inconsistent with other platforms and resulted in inconsistent event reporting (e.g. when a file is quickly removed and re-created), and generally a source of confusion. It was added in 2013 to fix a memory leak that no longer exists.

• all: return ErrNonExistentWatch when Remove() is called on a path that's not watched (#460)

• inotify: replace epoll() with non-blocking inotify (#434)

Non-blocking inotify was not generally available at the time this library was written in 2014, but now it is. As a result, the minimum Linux version is bumped from 2.6.27 to 2.6.32. This hugely simplifies the code and is faster.

• kqueue: don't check for events every 100ms (#480)

The watcher would wake up every 100ms, even when there was nothing to do. Now it waits until there is something to do.

• macos: retry opening files on EINTR (#475)

• kqueue: skip unreadable files (#479)

kqueue requires a file descriptor for every file in a directory; this would fail if a file was unreadable by the current user. Now these files are simply skipped.

• windows: fix renaming a watched directory if the parent is also watched (#370)

• windows: increase buffer size from 4K to 64K (#485)

• windows: close file handle on Remove() (#288)

• kqueue: put pathname in the error if watching a file fails (#471)

• inotify, windows: calling Close() more than once could race (#465)

• kqueue: improve Close() performance (#233)

• all: various documentation additions and clarifications.