Theoretically able to shut down a driver?

In practice, I can't get any combination of C's aeronmd, C++'s DriverTool, Rust's `aeronmd`, and `do_terminate`.

examples/aeronmd.rs

@@ -13,6 +13,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 static RUNNING: AtomicBool = AtomicBool::new(true);
 
 unsafe extern "C" fn termination_hook(_clientd: *mut c_void) {
+    println!("Terminated");
     RUNNING.store(false, Ordering::SeqCst);
 }
 

examples/do_terminate.rs

@@ -0,0 +1,51 @@
+use aeron_rs::client::cnc_descriptor::MetaDataDefinition;
+use aeron_rs::client::concurrent::atomic_buffer::AtomicBuffer;
+use aeron_rs::client::concurrent::ring_buffer::ManyToOneRingBuffer;
+use aeron_rs::client::context::ClientContext;
+use aeron_rs::util::IndexT;
+use memmap::MmapOptions;
+use std::fs::OpenOptions;
+use std::mem::size_of;
+
+fn main() {
+    let path = ClientContext::default_aeron_path();
+    let cnc = path.join("cnc.dat");
+
+    println!("Opening CnC file: {}", cnc.display());
+    let file = OpenOptions::new()
+        .read(true)
+        .write(true)
+        .open(&cnc)
+        .expect("Unable to open CnC file");
+    let mut mmap =
+        unsafe { MmapOptions::default().map_mut(&file) }.expect("Unable to mmap CnC file");
+    println!("MMap len: {}", mmap.len());
+
+    // When creating the buffer, we need to offset by the CnC metadata
+    let cnc_metadata_len = size_of::<MetaDataDefinition>();
+    println!("Buffer len: {}", mmap[cnc_metadata_len..].len());
+
+    // Read metadata to get buffer length
+    let buffer_len = {
+        let atomic_buffer = AtomicBuffer::wrap(&mut mmap);
+        let metadata = atomic_buffer.overlay::<MetaDataDefinition>(0).unwrap();
+        metadata.to_driver_buffer_length
+    };
+
+    let buffer_end = cnc_metadata_len + buffer_len as usize;
+    let atomic_buffer = AtomicBuffer::wrap(&mut mmap[cnc_metadata_len..buffer_end]);
+    let mut ring_buffer =
+        ManyToOneRingBuffer::wrap(atomic_buffer).expect("Improperly sized buffer");
+
+    // 20 bytes: Client ID (8), correlation ID (8), token length (4)
+    let mut terminate_bytes = vec![0u8; 20];
+    let terminate_len = terminate_bytes.len();
+    let mut source_buffer = AtomicBuffer::wrap(&mut terminate_bytes);
+    let client_id = ring_buffer.next_correlation_id();
+    source_buffer.put_i64_ordered(0, client_id).unwrap();
+
+    let term_id: i32 = 0x0E;
+    ring_buffer
+        .write(term_id, &source_buffer, 0, terminate_len as IndexT)
+        .unwrap();
+}

src/client/cnc_descriptor.rs

@@ -50,7 +50,8 @@
 #[repr(C, align(4))]
 pub struct MetaDataDefinition {
     cnc_version: i32,
-    _to_driver_buffer_length: i32,
+    /// Size of the buffer containing data going to the media driver
+    pub to_driver_buffer_length: i32,
     _to_client_buffer_length: i32,
     _counter_metadata_buffer_length: i32,
     _counter_values_buffer_length: i32,

src/client/concurrent/atomic_buffer.rs

@@ -34,8 +34,10 @@ impl<'a> AtomicBuffer<'a> {
         }
     }
 
-    #[allow(clippy::cast_ptr_alignment)]
-    fn overlay<T>(&self, offset: IndexT) -> Result<&T>
+    /// Overlay a struct on a buffer.
+    ///
+    /// NOTE: Has the potential to cause undefined behavior if alignment is incorrect.
+    pub fn overlay<T>(&self, offset: IndexT) -> Result<&T>
     where
         T: Sized,
     {

src/client/concurrent/ring_buffer.rs

@@ -199,7 +199,6 @@ impl<'a> ManyToOneRingBuffer<'a> {
                 .unwrap();
             let available_capacity = self.capacity - (tail - head) as IndexT;
 
-            println!("Available: {}", available_capacity);
             if required > available_capacity {
                 // UNWRAP: Known-valid offset calculated during initialization
                 head = self
@@ -225,7 +224,6 @@ impl<'a> ManyToOneRingBuffer<'a> {
             tail_index = (tail & i64::from(mask)) as IndexT;
             let to_buffer_end_length = self.capacity - tail_index;
 
-            println!("To buffer end: {}", to_buffer_end_length);
             if required > to_buffer_end_length {
                 let mut head_index = (head & i64::from(mask)) as IndexT;