device path: implement PartialEq+Eq for DevicePath (#265)

Author: nicholasbishop

src/proto/device_path.rs

@@ -17,6 +17,7 @@
 //! total size of the Node including the header.
 
 use crate::{proto::Protocol, unsafe_guid};
+use core::slice;
 
 /// Header that appears at the start of every [`DevicePath`] node.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -35,7 +36,7 @@ pub struct DevicePathHeader {
 /// This can be opened on a `LoadedImage.device()` handle using the `HandleProtocol` boot service.
 #[repr(C, packed)]
 #[unsafe_guid("09576e91-6d3f-11d2-8e39-00a0c969723b")]
-#[derive(Protocol)]
+#[derive(Eq, Protocol)]
 pub struct DevicePath {
     header: DevicePathHeader,
 }
@@ -70,6 +71,27 @@ impl DevicePath {
     }
 }
 
+impl PartialEq for DevicePath {
+    fn eq(&self, other: &DevicePath) -> bool {
+        // Check for equality with a byte-by-byte comparison of the device
+        // paths. Note that this covers the entire payload of the device path
+        // using the `length` field in the header, so it's not the same as just
+        // comparing the fields of the `DevicePath` struct.
+        unsafe {
+            let self_bytes = slice::from_raw_parts(
+                self as *const DevicePath as *const u8,
+                self.length() as usize,
+            );
+            let other_bytes = slice::from_raw_parts(
+                other as *const DevicePath as *const u8,
+                other.length() as usize,
+            );
+
+            self_bytes == other_bytes
+        }
+    }
+}
+
 /// Iterator over [`DevicePath`] nodes.
 ///
 /// Iteration ends when a path is reached where [`DevicePath::is_end_entire`]