diff --git a/inc/functions/fs.php b/inc/functions/fs.php
new file mode 100644
index 00000000..0c43d66a
--- /dev/null
+++ b/inc/functions/fs.php
@@ -0,0 +1,143 @@
+<?php
+
+namespace Vichan\Functions;
+
+
+class FsUtils {
+	public const ATOMIC_MULTI_ERR_NONE = 0;
+	public const ATOMIC_MULTI_ERR_SRC_BAD = 1;
+	public const ATOMIC_MULTI_ERR_SRC_NO_PERM = 2;
+	public const ATOMIC_MULTI_ERR_TARGET_BAD = 3;
+	public const ATOMIC_MULTI_ERR_TARGET_NO_PERM = 4;
+	public const ATOMIC_MULTI_ERR_ACTION_ERROR = 5;
+
+
+	private static function atomic_multi(array $config, string $src_dir, string $target_dir, iterable $src_file_names, callable $action, callable $action_rollback): int {
+		if (!is_dir($src_dir)) {
+			return self::ATOMIC_MULTI_ERR_SRC_BAD;
+		}
+		if (!is_readable($src_dir)) {
+			return self::ATOMIC_MULTI_ERR_SRC_NO_PERM;
+		}
+
+		if (!is_dir($target_dir)) {
+			return self::ATOMIC_MULTI_ERR_TARGET_BAD;
+		}
+		if (!is_writable($target_dir)) {
+			return self::ATOMIC_MULTI_ERR_TARGET_NO_PERM;
+		}
+
+		$src_dir = self::ensure_end_path_separator($src_dir);
+		$target_dir = self::ensure_end_path_separator($target_dir);
+
+		$linked = [];
+		foreach ($src_file_names as $file_name) {
+			$src_path = $src_dir . $file_name;
+			$target_path = $target_dir . $file_name;
+
+			$success = $action($src_path, $target_path);
+
+			if ($success) {
+				$linked[] = $file_name;
+			}
+			// Rollback.
+			else {
+				if ($config['syslog']) {
+					$l_count = count($linked);
+					_syslog(LOG_ERR, "Failed to link $src_path in $target_dir, rolling back $l_count linked files.");
+				}
+
+				foreach ($linked as $file_name) {
+					$src_path = $src_dir . $file_name;
+					$target_path = $target_dir . $file_name;
+
+					// Already falling back, ignore eventual errors and just log them.
+					$success = $action_rollback($src_path, $target_path);
+					if (!$success && $config['syslog']) {
+						_syslog(LOG_ERR, "Failed to rollback $target_path in $src_dir.");
+					}
+				}
+
+				return self::ATOMIC_MULTI_ERR_ACTION_ERROR;
+			}
+		}
+
+		return self::ATOMIC_MULTI_ERR_NONE;
+	}
+
+
+	/**
+	 * Appends a '/' to the given path if not already present.
+	 * @return string Returns the directory path terminating with a path separator.
+	 */
+	public static function ensure_end_path_separator(string $dir): string {
+		if ($dir[strlen($dir) - 1] !== '/') {
+			return "$dir/";
+		}
+		return $dir;
+	}
+
+	/**
+	 * Copies all the files or aborts and rolls back on error.
+	 * Implemented with file hardlinking.
+	 * @param array $config The configuration array.
+	 * @param string $src_dir The directory from which to fetch the files.
+	 * @param string $target_dir The directory to which the files should be copied to.
+	 * @param iterable $src_file_names The names of the files in $src_dir to be copied into $target_dir. The file names
+	 * 									must NOT begin with a path separator.
+	 * @return int Returns one of the class's ATOMIC_MULTI_ERR_* constants.
+	 */
+	public function atomic_multi_copy(array $config, string $src_dir, string $target_dir, iterable $src_file_names) {
+		self::atomic_multi($config, $src_dir, $target_dir, $src_file_names, 'link', function($src_path, $target_path) {
+			// Delete the hard links.
+			\unlink($target_path);
+		});
+	}
+
+	/**
+	 * Copies all the files or aborts and rolls back on error.
+	 * Implemented via file move.
+	 * @param array $config The configuration array.
+	 * @param string $src_dir The directory from which to fetch the files.
+	 * @param string $target_dir The directory to which the files should be copied to.
+	 * @param iterable $src_file_names The names of the files in $src_dir to be copied into $target_dir. The file names
+	 * 									must NOT begin with a path separator.
+	 * @return int Returns one of the class's ATOMIC_MULTI_ERR_* constants.
+	 */
+	public function atomic_multi_move(array $config, string $src_dir, string $target_dir, iterable $src_file_names) {
+		self::atomic_multi($config, $src_dir, $target_dir, $src_file_names, 'rename', function ($src_path, $target_path) {
+			// Move the files back into the source directory.
+			\rename($target_path, $src_path);
+		});
+	}
+
+	/**
+	 * Deletes all the files in the given directory.
+	 *
+	 * @param string $src_dir The directory from which to delete the files.
+	 * @param iterable $src_file_names The names of the files in $src_dir to be deleted. The file names must NOT begin
+	 * 									with a path separator.
+	 * @return int Returns the number of deleted files.
+	 */
+	public function multi_delete(array $config, string $dir, iterable $file_names): int {
+		$dir = self::ensure_end_path_separator($dir);
+		$deleted = 0;
+
+		foreach ($file_names as $file_name) {
+			$target_path = $dir . $file_name;
+
+			$success = \unlink($target_path);
+
+			if ($success) {
+				$deleted++;
+			} elseif ($config['syslog']) {
+				_syslog(LOG_ERR, "Failed to delete $target_path");
+			}
+		}
+
+		return $deleted;
+	}
+
+	// Static class.
+	private function __construct() {}
+}