cp: omit pipe() if input is pipe

Author: oech3

src/uucore/src/lib/features/buf_copy/linux.rs

@@ -39,21 +39,22 @@ where
     R: Read + AsFd + AsRawFd,
     S: Write + AsFd + AsRawFd,
 {
-    // If we're on Linux or Android, try to use the splice() system call
-    // for faster writing. If it works, we're done.
-    // todo: bypass broker pipe this if input or output is pipe. We use this mostly for stream.
-    if !crate::pipes::splice_unbounded_broker(src, dest)? {
-        return Ok(());
+    // try to use the splice() system call
+    // for faster writing. If it works, we're done
+    // todo: dedup with cat/src/splice.rs
+    let fallback = match crate::pipes::splice(&src, dest, crate::pipes::MAX_ROOTLESS_PIPE_SIZE) {
+        Ok(_) => crate::pipes::splice_unbounded(src, dest)?,
+        // both of in/output are not pipe
+        _ => crate::pipes::splice_unbounded_broker(src, dest)?,
+    };
+    if fallback {
+        std::io::copy(src, dest)?;
+        // If the splice() call failed and there has been some data written to
+        // stdout via while loop above AND there will be second splice() call
+        // that will succeed, data pushed through splice will be output before
+        // the data buffered in stdout.lock. Therefore additional explicit flush
+        // is required here.
+        dest.flush()?;
     }
-
-    // If the splice() call failed, fall back on slower writing.
-    std::io::copy(src, dest)?;
-
-    // If the splice() call failed and there has been some data written to
-    // stdout via while loop above AND there will be second splice() call
-    // that will succeed, data pushed through splice will be output before
-    // the data buffered in stdout.lock. Therefore additional explicit flush
-    // is required here.
-    dest.flush()?;
     Ok(())
 }