Add more from the std

library/std/src/sys/io/kernel_copy/mod.rs

@@ -0,0 +1,23 @@
+pub enum CopyState {
+    #[cfg_attr(not(any(target_os = "linux", target_os = "android")), expect(dead_code))]
+    Ended(u64),
+    Fallback(u64),
+}
+
+cfg_select! {
+    any(target_os = "linux", target_os = "android") => {
+        mod linux;
+        pub use linux::kernel_copy;
+    }
+    _ => {
+        use crate::io::{Result, Read, Write};
+
+        pub fn kernel_copy<R: ?Sized, W: ?Sized>(_reader: &mut R, _writer: &mut W) -> Result<CopyState>
+        where
+            R: Read,
+            W: Write,
+        {
+            Ok(CopyState::Fallback(0))
+        }
+    }
+}