yes: use tee syscall as pipe only fast-path

.vscode/cspell.dictionaries/workspace.wordlist.txt

@@ -8,6 +8,7 @@ advapi32-sys
 aho-corasick
 backtrace
 blake2b_simd
+rustix
 
 # * uutils project
 uutils
@@ -362,6 +363,7 @@ uutils
 
 # * function names
 getcwd
+setpipe
 
 # * other
 getlimits

Cargo.toml

@@ -435,6 +435,7 @@ rstest = "0.26.0"
 rstest_reuse = "0.7.0"
 rustc-hash = "2.1.1"
 rust-ini = "0.21.0"
+rustix = "1.1.4"
 same-file = "1.0.6"
 self_cell = "1.0.4"
 selinux = "=0.6.0"

src/uu/yes/Cargo.toml

@@ -22,6 +22,7 @@ path = "src/yes.rs"
 clap = { workspace = true }
 itertools = { workspace = true }
 fluent = { workspace = true }
+rustix = { workspace = true, features = ["pipe"] }
 
 [target.'cfg(unix)'.dependencies]
 uucore = { workspace = true, features = ["pipes", "signals"] }

src/uu/yes/src/yes.rs

@@ -13,8 +13,12 @@ use uucore::error::{UResult, USimpleError, strip_errno};
 use uucore::format_usage;
 use uucore::translate;
 
-// it's possible that using a smaller or larger buffer might provide better performance on some
-// systems, but honestly this is good enough
+#[cfg(any(target_os = "linux", target_os = "android"))]
+const MAX_ROOTLESS_PIPE_SIZE: usize = 1024 * 1024;
+// todo: investigate best rate
+#[cfg(any(target_os = "linux", target_os = "android"))]
+const BUF_SIZE: usize = MAX_ROOTLESS_PIPE_SIZE;
+#[cfg(not(any(target_os = "linux", target_os = "android")))]
 const BUF_SIZE: usize = 16 * 1024;
 
 #[uucore::main]
@@ -110,8 +114,25 @@ fn prepare_buffer(buf: &mut Vec<u8>) {
 
 pub fn exec(bytes: &[u8]) -> io::Result<()> {
     let stdout = io::stdout();
-    let mut stdout = stdout.lock();
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    {
+        use rustix::pipe::{SpliceFlags, fcntl_setpipe_size, pipe, tee};
+        // fast-path for pipe. todo: port the fast-path for > file
+        if let Ok((p_read, p_write)) = pipe() {
+            let _ = fcntl_setpipe_size(&p_read, MAX_ROOTLESS_PIPE_SIZE);
+            let _ = fcntl_setpipe_size(&stdout, MAX_ROOTLESS_PIPE_SIZE);
+            if std::fs::File::from(p_write).write_all(bytes).is_ok() {
+                while let Ok(1..) = tee(
+                    &p_read,
+                    &stdout,
+                    MAX_ROOTLESS_PIPE_SIZE,
+                    SpliceFlags::empty(),
+                ) {}
+            }
+        }
+    }
 
+    let mut stdout = stdout.lock();
     loop {
         stdout.write_all(bytes)?;
     }
@@ -122,6 +143,7 @@ mod tests {
     use super::*;
 
     #[test]
+    #[cfg(not(any(target_os = "linux", target_os = "android")))] // Linux uses different buffer size
     fn test_prepare_buffer() {
         let tests = [
             (150, 16350),

tests/by-util/test_yes.rs

@@ -70,7 +70,7 @@ fn test_long_input() {
     #[cfg(windows)]
     const TIMES: usize = 500;
     let arg = "abcdef".repeat(TIMES) + "\n";
-    let expected_out = arg.repeat(30);
+    let expected_out = arg.repeat(5);
     run(&[&arg[..arg.len() - 1]], expected_out.as_bytes());
 }