fixes #8220

implements the --exchange flag for linux systems with testing

Author: hz2

src/uu/mv/locales/en-US.ftl

@@ -26,6 +26,12 @@ mv-error-not-directory = target {$path}: Not a directory
 mv-error-target-not-directory = target directory {$path}: Not a directory
 mv-error-failed-access-not-directory = failed to access {$path}: Not a directory
 mv-error-backup-with-no-clobber = cannot combine --backup with -n/--no-clobber or --update=none-fail
+mv-error-exchange-needs-two-files = --exchange requires exactly two files to exchange
+mv-error-exchange-conflicts-with-target-directory = --exchange conflicts with --target-directory
+mv-error-exchange-conflicts-with-backup = --exchange conflicts with backup options
+mv-error-exchange-conflicts-with-update = --exchange conflicts with update options
+mv-error-exchange-not-supported = --exchange is not supported on this system
+mv-error-exchange-cross-device = --exchange requires both files to be on the same filesystem
 mv-error-extra-operand = mv: extra operand {$operand}
 mv-error-backup-might-destroy-source = backing up {$target} might destroy source;  {$source} not moved
 mv-error-will-not-overwrite-just-created = will not overwrite just-created '{$target}' with '{$source}'
@@ -48,6 +54,7 @@ mv-help-verbose = explain what is being done
 mv-help-progress = Display a progress bar.
   Note: this feature is not supported by GNU coreutils.
 mv-help-debug = explain how a file is copied. Implies -v
+mv-help-exchange = exchange two files atomically (Linux only)
 
 # Verbose messages
 mv-verbose-renamed = renamed {$from} -> {$to}

src/uu/mv/locales/fr-FR.ftl

@@ -26,6 +26,12 @@ mv-error-not-directory = cible {$path} : N'est pas un répertoire
 mv-error-target-not-directory = répertoire cible {$path} : N'est pas un répertoire
 mv-error-failed-access-not-directory = impossible d'accéder à {$path} : N'est pas un répertoire
 mv-error-backup-with-no-clobber = impossible de combiner --backup avec -n/--no-clobber ou --update=none-fail
+mv-error-exchange-needs-two-files = --exchange nécessite exactement deux fichiers à échanger
+mv-error-exchange-conflicts-with-target-directory = --exchange est en conflit avec --target-directory
+mv-error-exchange-conflicts-with-backup = --exchange est en conflit avec les options de sauvegarde
+mv-error-exchange-conflicts-with-update = --exchange est en conflit avec les options de mise à jour
+mv-error-exchange-not-supported = --exchange n'est pas pris en charge sur ce système
+mv-error-exchange-cross-device = --exchange nécessite que les deux fichiers soient sur le même système de fichiers
 mv-error-extra-operand = mv : opérande supplémentaire {$operand}
 mv-error-backup-might-destroy-source = sauvegarder {$target} pourrait détruire la source ; {$source} non déplacé
 mv-error-will-not-overwrite-just-created = ne va pas écraser le fichier qui vient d'être créé '{$target}' avec '{$source}'
@@ -48,6 +54,7 @@ mv-help-verbose = expliquer ce qui est fait
 mv-help-progress = Afficher une barre de progression.
   Note : cette fonctionnalité n'est pas supportée par GNU coreutils.
 mv-help-debug = expliquer comment un fichier est copié. Implique -v
+mv-help-exchange = échanger deux fichiers de manière atomique (Linux uniquement)
 
 # Messages verbeux
 mv-verbose-renamed = renommé {$from} -> {$to}

src/uu/mv/src/mv.rs

@@ -97,6 +97,9 @@ pub struct Options {
 
     /// `--debug`
     pub debug: bool,
+
+    /// `--exchange`
+    pub exchange: bool,
 }
 
 impl Default for Options {
@@ -112,6 +115,7 @@ impl Default for Options {
             strip_slashes: false,
             progress_bar: false,
             debug: false,
+            exchange: false,
         }
     }
 }
@@ -138,6 +142,7 @@ static OPT_VERBOSE: &str = "verbose";
 static OPT_PROGRESS: &str = "progress";
 static ARG_FILES: &str = "files";
 static OPT_DEBUG: &str = "debug";
+static OPT_EXCHANGE: &str = "exchange";
 
 #[uucore::main]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
@@ -175,6 +180,34 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         ));
     }
 
+    // Validate exchange flag
+    if matches.get_flag(OPT_EXCHANGE) {
+        if files.len() != 2 {
+            return Err(UUsageError::new(
+                1,
+                get_message("mv-error-exchange-needs-two-files"),
+            ));
+        }
+        if matches.contains_id(OPT_TARGET_DIRECTORY) {
+            return Err(UUsageError::new(
+                1,
+                get_message("mv-error-exchange-conflicts-with-target-directory"),
+            ));
+        }
+        if backup_mode != BackupMode::None {
+            return Err(UUsageError::new(
+                1,
+                get_message("mv-error-exchange-conflicts-with-backup"),
+            ));
+        }
+        if update_mode != UpdateMode::All {
+            return Err(UUsageError::new(
+                1,
+                get_message("mv-error-exchange-conflicts-with-update"),
+            ));
+        }
+    }
+
     let backup_suffix = backup_control::determine_backup_suffix(&matches);
 
     let target_dir = matches
@@ -198,6 +231,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         strip_slashes: matches.get_flag(OPT_STRIP_TRAILING_SLASHES),
         progress_bar: matches.get_flag(OPT_PROGRESS),
         debug: matches.get_flag(OPT_DEBUG),
+        exchange: matches.get_flag(OPT_EXCHANGE),
     };
 
     mv(&files[..], &opts)
@@ -294,6 +328,12 @@ pub fn uu_app() -> Command {
                 .help(get_message("mv-help-debug"))
                 .action(ArgAction::SetTrue),
         )
+        .arg(
+            Arg::new(OPT_EXCHANGE)
+                .long(OPT_EXCHANGE)
+                .help(get_message("mv-help-exchange"))
+                .action(ArgAction::SetTrue),
+        )
 }
 
 fn determine_overwrite_mode(matches: &ArgMatches) -> OverwriteMode {
@@ -311,6 +351,73 @@ fn determine_overwrite_mode(matches: &ArgMatches) -> OverwriteMode {
     }
 }
 
+/// Atomically exchange two files using renameat2 with RENAME_EXCHANGE
+#[cfg(target_os = "linux")]
+fn exchange_files(path1: &Path, path2: &Path, opts: &Options) -> UResult<()> {
+    use std::ffi::CString;
+    use std::os::unix::ffi::OsStrExt;
+
+    // Convert paths to C strings
+    let c_path1 = CString::new(path1.as_os_str().as_bytes())
+        .map_err(|e| USimpleError::new(1, format!("Invalid path {}: {}", path1.display(), e)))?;
+    let c_path2 = CString::new(path2.as_os_str().as_bytes())
+        .map_err(|e| USimpleError::new(1, format!("Invalid path {}: {}", path2.display(), e)))?;
+
+    // RENAME_EXCHANGE flag for renameat2
+    const RENAME_EXCHANGE: libc::c_int = 2;
+
+    // Use renameat2 to atomically exchange the files
+    let result = unsafe {
+        libc::syscall(
+            libc::SYS_renameat2,
+            libc::AT_FDCWD,
+            c_path1.as_ptr(),
+            libc::AT_FDCWD,
+            c_path2.as_ptr(),
+            RENAME_EXCHANGE,
+        )
+    };
+
+    if result == 0 {
+        if opts.verbose {
+            println!("{} <-> {}", path1.display(), path2.display());
+        }
+        Ok(())
+    } else {
+        let errno = unsafe { *libc::__errno_location() };
+        match errno {
+            libc::ENOTSUP | libc::EINVAL => Err(USimpleError::new(
+                1,
+                get_message("mv-error-exchange-not-supported"),
+            )),
+            libc::ENOENT => {
+                let missing_path = if !path1.exists() { path1 } else { path2 };
+                Err(MvError::NoSuchFile(missing_path.display().to_string()).into())
+            }
+            libc::EXDEV => Err(USimpleError::new(
+                1,
+                get_message("mv-error-exchange-cross-device"),
+            )),
+            _ => {
+                let error_msg = std::io::Error::from_raw_os_error(errno);
+                Err(USimpleError::new(
+                    1,
+                    format!("exchange failed: {}", error_msg),
+                ))
+            }
+        }
+    }
+}
+
+/// Fallback exchange implementation for non-Linux systems
+#[cfg(not(target_os = "linux"))]
+fn exchange_files(_path1: &Path, _path2: &Path, _opts: &Options) -> UResult<()> {
+    Err(USimpleError::new(
+        1,
+        get_message("mv-error-exchange-not-supported"),
+    ))
+}
+
 fn parse_paths(files: &[OsString], opts: &Options) -> Vec<PathBuf> {
     let paths = files.iter().map(Path::new);
 
@@ -536,6 +643,17 @@ fn handle_multiple_paths(paths: &[PathBuf], opts: &Options) -> UResult<()> {
 pub fn mv(files: &[OsString], opts: &Options) -> UResult<()> {
     let paths = parse_paths(files, opts);
 
+    // Handle exchange mode
+    if opts.exchange {
+        if paths.len() != 2 {
+            return Err(USimpleError::new(
+                1,
+                get_message("mv-error-exchange-needs-two-files"),
+            ));
+        }
+        return exchange_files(&paths[0], &paths[1], opts);
+    }
+
     if let Some(ref name) = opts.target_dir {
         return move_files_into_dir(&paths, &PathBuf::from(name), opts);
     }

tests/by-util/test_mv.rs

@@ -2488,3 +2488,140 @@ fn test_mv_cross_device_permission_denied() {
     set_permissions(other_fs_tempdir.path(), PermissionsExt::from_mode(0o755))
         .expect("Unable to restore directory permissions");
 }
+
+// Tests for --exchange flag
+#[test]
+#[cfg(target_os = "linux")]
+fn test_mv_exchange_basic() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    at.write("file2", "content2");
+
+    ucmd.arg("--exchange").arg("file1").arg("file2").succeeds();
+
+    // After exchange, file1 should have content2 and file2 should have content1
+    assert_eq!(at.read("file1"), "content2");
+    assert_eq!(at.read("file2"), "content1");
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_mv_exchange_verbose() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    at.write("file2", "content2");
+
+    ucmd.arg("--exchange")
+        .arg("--verbose")
+        .arg("file1")
+        .arg("file2")
+        .succeeds()
+        .stdout_contains("file1 <-> file2");
+}
+
+#[test]
+fn test_mv_exchange_wrong_number_of_args() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+
+    ucmd.arg("--exchange")
+        .arg("file1")
+        .fails()
+        .stderr_contains("requires at least 2 values");
+}
+
+#[test]
+fn test_mv_exchange_three_files() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    at.write("file2", "content2");
+    at.write("file3", "content3");
+
+    ucmd.arg("--exchange")
+        .arg("file1")
+        .arg("file2")
+        .arg("file3")
+        .fails()
+        .stderr_contains("--exchange requires exactly two files");
+}
+
+#[test]
+fn test_mv_exchange_conflicts_with_target_directory() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    at.write("file2", "content2");
+    at.mkdir("dir");
+
+    ucmd.arg("--exchange")
+        .arg("--target-directory")
+        .arg("dir")
+        .arg("file1")
+        .arg("file2")
+        .fails()
+        .stderr_contains("--exchange conflicts with --target-directory");
+}
+
+#[test]
+fn test_mv_exchange_conflicts_with_backup() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    at.write("file2", "content2");
+
+    ucmd.arg("--exchange")
+        .arg("--backup")
+        .arg("file1")
+        .arg("file2")
+        .fails()
+        .stderr_contains("--exchange conflicts with backup options");
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_mv_exchange_missing_file() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    // file2 doesn't exist
+
+    ucmd.arg("--exchange")
+        .arg("file1")
+        .arg("file2")
+        .fails()
+        .stderr_contains("cannot stat file2: No such file or directory");
+}
+
+#[test]
+#[cfg(not(target_os = "linux"))]
+fn test_mv_exchange_missing_file() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    // file2 doesn't exist
+
+    ucmd.arg("--exchange")
+        .arg("file1")
+        .arg("file2")
+        .fails()
+        .stderr_contains("--exchange is not supported on this system");
+}
+
+#[test]
+#[cfg(not(target_os = "linux"))]
+fn test_mv_exchange_not_supported() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.write("file1", "content1");
+    at.write("file2", "content2");
+
+    ucmd.arg("--exchange")
+        .arg("file1")
+        .arg("file2")
+        .fails()
+        .stderr_contains("--exchange is not supported on this system");
+}