sync: fsync() file operands when no -d/-f flags (GNU MODE_FILE compat)

src/uu/sync/src/sync.rs

@@ -86,6 +86,11 @@ mod platform {
     pub fn do_fdatasync(files: &[String]) -> UResult<()> {
         do_sync_with(files, rustix::fs::fdatasync)
     }
+
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    pub fn do_fsync(files: &[String]) -> UResult<()> {
+        do_sync_with(files, rustix::fs::fsync)
+    }
 }
 
 #[cfg(windows)]
@@ -254,6 +259,9 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     } else if matches.get_flag(options::DATA) {
         #[cfg(any(target_os = "linux", target_os = "android"))]
         fdatasync(&files)?;
+    } else if !files.is_empty() {
+        #[cfg(any(target_os = "linux", target_os = "android"))]
+        fsync(&files)?;
     } else {
         sync()?;
     }
@@ -303,3 +311,8 @@ fn syncfs(files: &[String]) -> UResult<()> {
 fn fdatasync(files: &[String]) -> UResult<()> {
     platform::do_fdatasync(files)
 }
+
+#[cfg(any(target_os = "linux", target_os = "android"))]
+fn fsync(files: &[String]) -> UResult<()> {
+    platform::do_fsync(files)
+}

tests/by-util/test_sync.rs

@@ -143,6 +143,19 @@ fn test_sync_fdatasync_error_handling() {
         .stderr_contains("error opening");
 }
 
+#[cfg(any(target_os = "linux", target_os = "android"))]
+#[test]
+fn test_sync_file_operands_fsync_each_file() {
+    // Regression test: `sync FILE` (no -d/-f flags) must fsync each file
+    // like GNU coreutils, not fall back to a global sync() that ignores
+    // the operands. /proc/self/mem rejects fsync() with EINVAL, so this
+    // must fail; a global sync() would wrongly exit 0.
+    new_ucmd!()
+        .arg("/dev/null")
+        .fails_with_code(1)
+        .stderr_contains("error syncing");
+}
+
 #[cfg(target_vendor = "apple")]
 #[test]
 fn test_sync_syncfs_error_handling_macos() {