refactor: remove magic numbers

general/echo/kmdf/driver/DriverSync/src/device.rs

@@ -30,6 +30,19 @@ use crate::{
     WDF_REQUEST_CONTEXT_TYPE_INFO,
 };
 
+/// Number of 100-nanosecond intervals in one millisecond. WDF relative times
+/// are expressed in 100-nanosecond units, so this converts a millisecond delay
+/// into the units WDF expects.
+const RELATIVE_100_NS_INTERVALS_PER_MS: i64 = 10_000;
+
+/// Delay, in milliseconds, before the periodic timer first fires once the
+/// device has started.
+const START_TIMER_DUE_TIME_MS: i64 = 100;
+
+/// 100ms relative time (in 100-nanosecond units). The negative sign marks the
+/// value as a relative (rather than absolute) timeout.
+const WDF_REL_TIMEOUT_IN_MS: i64 = -START_TIMER_DUE_TIME_MS * RELATIVE_100_NS_INTERVALS_PER_MS;
+
 /// Worker routine called to create a device and its software resources.
 ///
 /// # Arguments:
@@ -162,7 +175,7 @@ extern "C" fn echo_evt_device_self_managed_io_start(device: WDFDEVICE) -> NTSTAT
     // into low power state.
     unsafe { call_unsafe_wdf_function_binding!(WdfIoQueueStart, queue) };
 
-    let due_time: i64 = -(100) * (10000);
+    let due_time: i64 = WDF_REL_TIMEOUT_IN_MS;
 
     let _ = unsafe { (*queue_context).timer.start(due_time) };
 

general/echo/kmdf/driver/DriverSync/src/driver.rs

@@ -177,9 +177,15 @@ fn echo_print_driver_version() -> NTSTATUS {
         call_unsafe_wdf_function_binding!(WdfDriverIsVersionAvailable, driver, &raw mut ver)
     } > 0
     {
-        println!("Yes, framework version is 1.0");
+        println!(
+            "Yes, framework version is {}.{}",
+            ver.MajorVersion, ver.MinorVersion
+        );
     } else {
-        println!("No, framework version is not 1.0");
+        println!(
+            "No, framework version is not {}.{}",
+            ver.MajorVersion, ver.MinorVersion
+        );
     }
 
     STATUS_SUCCESS

general/echo/kmdf/driver/DriverSync/src/queue.rs

@@ -44,11 +44,33 @@ use crate::{
     WDF_TIMER_CONFIG_SIZE,
 };
 
-/// Set max write length for testing
-const MAX_WRITE_LENGTH: usize = 1024 * 40;
+/// Number of bytes in one kilobyte.
+const BYTES_PER_KB: usize = 1024;
 
-/// Set timer period in ms
-const TIMER_PERIOD: u32 = 1000 * 10;
+/// Max write length, in bytes, for testing
+const MAX_WRITE_LENGTH: usize = 40 * BYTES_PER_KB;
+
+/// Number of milliseconds in one second.
+const MS_PER_SECOND: u32 = 1000;
+
+/// Watchdog timer period, in seconds.
+const TIMER_PERIOD_SECONDS: u32 = 10;
+
+/// Timer period in ms
+const TIMER_PERIOD: u32 = TIMER_PERIOD_SECONDS * MS_PER_SECOND;
+
+/// Non-zero char literal (of one to four chars) for pool tag used in
+/// `ExAllocatePool2`
+const MEMORY_TAG: u32 = u32::from_be_bytes(*b"sam1");
+
+/// Initial cancel/completion ownership count assigned to a new request. A
+/// claimant takes ownership by decrementing the count down to zero.
+const INITIAL_CANCEL_OWNERSHIP_COUNT: i32 = 1;
+
+/// Total ownership count held by the timer DPC once it has claimed completion
+/// of a request: the initial count plus the single increment it acquired via
+/// `echo_increment_request_cancel_ownership_count`.
+const TIMER_CLAIMED_OWNERSHIP_COUNT: i32 = INITIAL_CANCEL_OWNERSHIP_COUNT + 1;
 
 /// This routine will interlock increment a value only if the current value
 /// is greater then the floor value.
@@ -356,7 +378,8 @@ fn echo_set_current_request(request: WDFREQUEST, queue: WDFQUEUE) {
     // they will interlock decrement the count.  When the count reaches zero,
     // ownership has been acquired and the caller may complete the request.
     unsafe {
-        (*request_context).cancel_completion_ownership_count = AtomicI32::new(1);
+        (*request_context).cancel_completion_ownership_count =
+            AtomicI32::new(INITIAL_CANCEL_OWNERSHIP_COUNT);
     }
 
     // Defer the completion to another thread from the timer dpc
@@ -564,9 +587,8 @@ extern "C" fn echo_evt_io_write(queue: WDFQUEUE, request: WDFREQUEST, length: us
             (*queue_context).length = 0;
         }
 
-        // FIXME: Memory Tag
         (*queue_context).buffer =
-            ExAllocatePool2(POOL_FLAG_NON_PAGED, length as SIZE_T, 's' as u32);
+            ExAllocatePool2(POOL_FLAG_NON_PAGED, length as SIZE_T, MEMORY_TAG);
         if (*queue_context).buffer.is_null() {
             println!(
                 "echo_evt_io_write Could not allocate {:?} byte buffer",
@@ -697,12 +719,12 @@ unsafe extern "C" fn echo_evt_timer_func(timer: WDFTIMER) {
             // currently racing with it), there is no need to use an interlocked
             // decrement to lower the cancel ownership count.
 
-            // 2 is the initial count we set when we initialized
-            // CancelCompletionOwnershipCount plus the call to
+            // TIMER_CLAIMED_OWNERSHIP_COUNT is the initial count we set when we
+            // initialized CancelCompletionOwnershipCount plus the call to
             // EchoIncrementRequestCancelOwnershipCount()
             (*request_context)
                 .cancel_completion_ownership_count
-                .fetch_sub(2, Ordering::SeqCst);
+                .fetch_sub(TIMER_CLAIMED_OWNERSHIP_COUNT, Ordering::SeqCst);
             complete_request = true;
         }
     }

general/echo/kmdf/exe/src/main.rs

@@ -70,6 +70,16 @@ static READER_TYPE: u32 = 1;
 static WRITER_TYPE: u32 = 2;
 static NUM_ASYNCH_IO: usize = 100;
 static BUFFER_SIZE: usize = 40 * 1024;
+/// Transfer length, in bytes, for the first synchronous write/read test.
+static SYNC_TEST_SMALL_LENGTH: u32 = 512;
+/// Transfer length, in bytes, for the second synchronous write/read test.
+static SYNC_TEST_LARGE_LENGTH: u32 = 30 * 1024;
+/// Completion key associated with the device handle on the I/O completion port.
+static COMPLETION_PORT_KEY: usize = 1;
+/// Number of concurrent threads allowed to run for the I/O completion port.
+/// Zero lets the system allow as many concurrent threads as there are
+/// processors.
+static COMPLETION_PORT_CONCURRENT_THREADS: u32 = 0;
 
 fn main() -> Result<(), Box<dyn Error>> {
     let argument_vector: Vec<String> = env::args().collect();
@@ -155,9 +165,9 @@ Exit the app anytime by pressing Ctrl-C
 
         h.join().unwrap().unwrap();
     } else {
-        perform_write_read_test(h_device, 512)?;
+        perform_write_read_test(h_device, SYNC_TEST_SMALL_LENGTH)?;
 
-        perform_write_read_test(h_device, 30 * 1024)?;
+        perform_write_read_test(h_device, SYNC_TEST_LARGE_LENGTH)?;
     }
 
     Ok(())
@@ -334,7 +344,12 @@ fn async_io_work(io_type: u32) -> Result<(), Box<dyn Error>> {
     // Call Win32 API FFI CreateIoCompletionPort to get handle for completing async
     // requests
     unsafe {
-        h_completion_port = CreateIoCompletionPort(h_device, std::ptr::null_mut(), 1, 0);
+        h_completion_port = CreateIoCompletionPort(
+            h_device,
+            std::ptr::null_mut(),
+            COMPLETION_PORT_KEY,
+            COMPLETION_PORT_CONCURRENT_THREADS,
+        );
     }
 
     if h_completion_port.is_null() {