Inotify::read_events does not read all events

[jimblandy]

The documentation for Inotify::read_events says:

Returns any available events

Returns an iterator over all events that are currently available.

However, the function only reads one buffers' worth of data from the inotify file descriptor; if there are more events available than can fit in the buffer, the returned Events iterator returns None without trying to read any more from the file descriptor.

This causes the notify crate to delay reporting events. That crate registers its inotify file descriptor with mio::PollOpt::edge(), which requests edge-triggered notifications, as described here: https://docs.rs/mio/0.6.15/mio/struct.Poll.html#edge-triggered-and-level-triggered

If when the socket was registered with Poll, edge triggered events were requested, then the call to Poll::poll done in step 5 will (probably) hang despite there being another 1kb still present in the socket read buffer. The reason for this is that edge-triggered mode delivers events only when changes occur on the monitored Evented. So, in step 5 the caller might end up waiting for some data that is already present inside the socket buffer.

This means that notify::inotify::EventLoop::handle_inotify is indeed counting on inotify::Inotify::read_events to behave as documented: to fully consume all available data from the file descriptor. Indeed, if I change notify::inotify::EventLoop::new to request level-triggered events on inotify_fd, I get all my file creation notifications.