pipes.rs: replace bool by Result<(),()>

src/uu/cat/src/cat.rs

@@ -481,7 +481,7 @@ fn print_fast<R: FdReadable>(handle: &mut InputHandle<R>) -> CatResult<()> {
     let mut stdout = stdout;
     // Try to use the splice() system call for faster writing. If it works, we're done.
     #[cfg(any(target_os = "linux", target_os = "android"))]
-    if !uucore::pipes::splice_unbounded_auto(&handle.reader, &mut stdout)?
+    if uucore::pipes::splice_unbounded_auto(&handle.reader, &mut stdout)?.is_ok()
         && !uucore::pipes::might_fuse(&handle.reader)
     {
         return Ok(());

src/uu/tail/src/tail.rs

@@ -596,7 +596,7 @@ fn print_target_section<
         }
     } else {
         #[cfg(any(target_os = "linux", target_os = "android"))]
-        if uucore::pipes::splice_unbounded_auto(file, &mut stdout)? {
+        if uucore::pipes::splice_unbounded_auto(file, &mut stdout)?.is_err() {
             io::copy(file, &mut stdout)?;
         }
         #[cfg(not(any(target_os = "linux", target_os = "android")))]

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

@@ -23,7 +23,7 @@ pub fn copy_stream(
 ) -> crate::error::UResult<()> {
     // If we're on Linux or Android, try to use the splice() system call
     // for faster writing. If it works, we're done.
-    if crate::pipes::splice_unbounded_auto(src, dest)? {
+    if crate::pipes::splice_unbounded_auto(src, dest)?.is_err() {
         // If the splice() call failed, fall back on writing "without buffering", or order of output would be wrong
         // unrelated for cp /dev/stdin since cp does not have multiple input? <https://github.com/uutils/coreutils/issues/5186>
         // RawWriter also removes io::copy's specialization

src/uucore/src/lib/features/pipes.rs

@@ -142,16 +142,17 @@ pub fn splice_unbounded_broker(
 
 /// try splice_unbounded 1st and splice_unbounded_broker if both of in/output are not pipe
 ///
-/// return true if write fallback is needed
-/// (the fallback will be embedded to this function in the future)
+/// see splice_unbounded_broker to handle returned error
 #[inline]
-pub fn splice_unbounded_auto(source: &impl AsFd, dest: &mut impl AsFd) -> std::io::Result<bool> {
-    // use splice to check that input or output is pipe which is efficient
-    let fallback = match splice(&source, dest, MAX_ROOTLESS_PIPE_SIZE) {
-        Ok(_) => splice_unbounded(source, dest).is_err(),
-        _ => splice_unbounded_broker(source, dest)?.is_err(),
-    };
-    Ok(fallback)
+pub fn splice_unbounded_auto(
+    source: &impl AsFd,
+    dest: &mut impl AsFd,
+) -> std::io::Result<Result<(), ()>> {
+    if splice_unbounded(source, dest).is_err() {
+        // input or output is not pipe
+        return splice_unbounded_broker(source, dest);
+    }
+    Ok(Ok(()))
 }
 
 /// splice `n` bytes with read/write fallback