Use pwritev rather than copy_file_range, as it may be too recent

Also, tentatively fix "mismatched types" error for non-64b arch

src/uu/cp/src/cp.rs

@@ -9,7 +9,7 @@
 // For the full copyright and license information, please view the LICENSE file
 // that was distributed with this source code.
 
-// spell-checker:ignore (ToDO) ficlone ftruncate linkgs lstat nlink nlinks pathbuf reflink strs xattrs symlinked
+// spell-checker:ignore (ToDO) ficlone ftruncate linkgs lstat nlink nlinks pathbuf pwrite reflink strs xattrs symlinked
 
 #[macro_use]
 extern crate quick_error;
@@ -1617,7 +1617,7 @@ fn copy_on_write_linux(
         }
         (_, SparseMode::Always) => unsafe {
             let size: usize = src_file.metadata()?.size().try_into().unwrap();
-            if libc::ftruncate(dst_file.as_raw_fd(), i64::try_from(size).unwrap()) < 0 {
+            if libc::ftruncate(dst_file.as_raw_fd(), size.try_into().unwrap()) < 0 {
                 return Err(format!(
                     "failed to ftruncate {:?} to size {}: {}",
                     dest,
@@ -1633,25 +1633,18 @@ fn copy_on_write_linux(
 
             while current_offset < size {
                 use std::io::Read;
-                let (mut off_src, mut off_dst): (i64, i64) = (
-                    current_offset.try_into().unwrap(),
-                    current_offset.try_into().unwrap(),
-                );
 
                 let this_read = src_file.read(&mut buf)?;
-                current_offset += this_read;
 
                 if buf.iter().any(|&x| x != 0) {
-                    const COPY_FLAGS: u32 = 0;
-                    libc::copy_file_range(
-                        src_file.as_raw_fd(),
-                        &mut off_src,
+                    libc::pwrite(
                         dst_file.as_raw_fd(),
-                        &mut off_dst,
+                        buf.as_ptr() as *const libc::c_void,
                         this_read,
-                        COPY_FLAGS,
+                        current_offset.try_into().unwrap(),
                     );
                 }
+                current_offset += this_read;
             }
             Ok(())
         },