yes: match with GNU's strace behaviour

src/uu/yes/src/yes.rs

@@ -111,23 +111,21 @@ pub fn exec(bytes: &[u8]) -> io::Result<()> {
     let stdout = rustix::stdio::stdout();
     // improve throughput
     let _ = rustix::pipe::fcntl_setpipe_size(stdout, MAX_ROOTLESS_PIPE_SIZE);
-    // don't show any error from fast-path and fallback to write for proper message
+    // GNU catches all strace injections for zero-copy syscalls except for 1st one (checking support of it)
     // tee() cannot control offset. We can do tee only if original bytes.len() is multiple of PIPE_BUF,
     // but it is slower than mixing splice even it reduces syscalls...
+    let bytes_len = bytes.len();
     if let Ok((p_read, mut p_write)) = pipe::<true>()
         && p_write.write_all(bytes).is_ok()
         && let Ok((broker_read, broker_write)) = pipe::<true>()
+        && Ok(bytes_len) == tee(&p_read, &broker_write, MAX_ROOTLESS_PIPE_SIZE)
+        && uucore::pipes::drain_pipe(&broker_read, &stdout, bytes_len)?.is_ok()
     {
-        'splice: while let Ok(mut remain) = tee(&p_read, &broker_write, MAX_ROOTLESS_PIPE_SIZE) {
-            debug_assert!(remain == bytes.len(), "splice() should cleanup pipe");
+        // fallback from tee() is possible since we did not send anything to stdout yet
+        while let Ok(mut remain) = tee(&p_read, &broker_write, MAX_ROOTLESS_PIPE_SIZE) {
+            debug_assert!(remain == bytes_len, "splice should cleanup pipe");
             while remain > 0 {
-                if let Ok(s) = splice(&broker_read, &stdout, remain) {
-                    remain -= s;
-                } else {
-                    // avoid output breakage with reduced remain even if it would not happen
-                    RawWriter(stdout).write_all(&bytes[bytes.len() - remain..])?;
-                    break 'splice;
-                }
+                remain -= splice(&broker_read, &stdout, remain)?;
             }
         }
     }