From 9eae6db10a532f0f5b80ebac605ea88ecbb1d0ef Mon Sep 17 00:00:00 2001
From: oech3 <79379754+oech3@users.noreply.github.com>
Date: Tue, 31 Mar 2026 11:21:43 +0900
Subject: [PATCH] cat: avoid pipe() if stdout is pipe

---
 .../workspace.wordlist.txt                    |  2 +-
 src/uu/cat/src/splice.rs                      | 53 +++++++++++--------
 src/uucore/src/lib/features/pipes.rs          |  6 +--
 3 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/.vscode/cspell.dictionaries/workspace.wordlist.txt b/.vscode/cspell.dictionaries/workspace.wordlist.txt
index a32ca0770..04a140215 100644
--- a/.vscode/cspell.dictionaries/workspace.wordlist.txt
+++ b/.vscode/cspell.dictionaries/workspace.wordlist.txt
@@ -367,6 +367,7 @@ uutils
 
 # * function names
 getcwd
+setpipe
 
 # * other
 getlimits
@@ -374,7 +375,6 @@ weblate
 algs
 wasm
 wasip
-SETPIPE
 
 # * stty terminal flags
 brkint
diff --git a/src/uu/cat/src/splice.rs b/src/uu/cat/src/splice.rs
index 268f0296c..14e88dd6e 100644
--- a/src/uu/cat/src/splice.rs
+++ b/src/uu/cat/src/splice.rs
@@ -23,33 +23,40 @@ pub(super) fn write_fast_using_splice<R: FdReadable, S: AsRawFd + AsFd>(
     handle: &InputHandle<R>,
     write_fd: &S,
 ) -> CatResult<bool> {
-    use nix::fcntl::{FcntlArg, fcntl};
-    let (pipe_rd, pipe_wr) = pipe()?;
-    // improve performance
-    let _ = fcntl(
-        write_fd,
-        FcntlArg::F_SETPIPE_SZ(MAX_ROOTLESS_PIPE_SIZE as i32),
-    );
-
-    loop {
-        match splice(&handle.reader, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
-            Ok(n) => {
-                if n == 0 {
-                    return Ok(false);
+    const FIRST_PIPE_SIZE: usize = 64 * 1024;
+    if splice(&handle.reader, &write_fd, FIRST_PIPE_SIZE).is_ok() {
+        // fcntl improves performance for large file which is large overhead for small files
+        let _ = rustix::pipe::fcntl_setpipe_size(write_fd, MAX_ROOTLESS_PIPE_SIZE);
+        loop {
+            match splice(&handle.reader, &write_fd, MAX_ROOTLESS_PIPE_SIZE) {
+                Ok(1..) => {}
+                Ok(0) => return Ok(false),
+                Err(_) => return Ok(true),
+            }
+        }
+    } else {
+        // output is not pipe. Needs broker to use splice() which is high cost for small files
+        let (pipe_rd, pipe_wr) = pipe()?;
+        loop {
+            match splice(&handle.reader, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
+                Ok(n) => {
+                    if n == 0 {
+                        return Ok(false);
+                    }
+                    if splice_exact(&pipe_rd, write_fd, n).is_err() {
+                        // If the first splice manages to copy to the intermediate
+                        // pipe, but the second splice to stdout fails for some reason
+                        // we can recover by copying the data that we have from the
+                        // intermediate pipe to stdout using normal read/write. Then
+                        // we tell the caller to fall back.
+                        copy_exact(&pipe_rd, write_fd, n)?;
+                        return Ok(true);
+                    }
                 }
-                if splice_exact(&pipe_rd, write_fd, n).is_err() {
-                    // If the first splice manages to copy to the intermediate
-                    // pipe, but the second splice to stdout fails for some reason
-                    // we can recover by copying the data that we have from the
-                    // intermediate pipe to stdout using normal read/write. Then
-                    // we tell the caller to fall back.
-                    copy_exact(&pipe_rd, write_fd, n)?;
+                Err(_) => {
                     return Ok(true);
                 }
             }
-            Err(_) => {
-                return Ok(true);
-            }
         }
     }
 }
diff --git a/src/uucore/src/lib/features/pipes.rs b/src/uucore/src/lib/features/pipes.rs
index 6f613558e..2615912c0 100644
--- a/src/uucore/src/lib/features/pipes.rs
+++ b/src/uucore/src/lib/features/pipes.rs
@@ -5,12 +5,12 @@
 
 //! Thin zero-copy-related wrappers around functions from the `rustix` crate.
 
+#[cfg(any(target_os = "linux", target_os = "android"))]
+use rustix::pipe::{SpliceFlags, fcntl_setpipe_size};
 #[cfg(any(target_os = "linux", target_os = "android"))]
 use std::fs::File;
 #[cfg(any(target_os = "linux", target_os = "android"))]
 use std::os::fd::AsFd;
-#[cfg(any(target_os = "linux", target_os = "android"))]
-use rustix::pipe::SpliceFlags;
 pub const MAX_ROOTLESS_PIPE_SIZE: usize = 1024 * 1024;
 
 /// A wrapper around [`rustix::pipe::pipe`] that ensures the pipe is cleaned up.
@@ -22,7 +22,7 @@ pub const MAX_ROOTLESS_PIPE_SIZE: usize = 1024 * 1024;
 pub fn pipe() -> std::io::Result<(File, File)> {
     let (read, write) = rustix::pipe::pipe()?;
     // improve performance for splice
-    let _ = fcntl(&read, FcntlArg::F_SETPIPE_SZ(MAX_ROOTLESS_PIPE_SIZE as i32));
+    let _ = fcntl_setpipe_size(&read, MAX_ROOTLESS_PIPE_SIZE);
 
     Ok((File::from(read), File::from(write)))
 }