/*
 * mv-sync: atomic rename that fails if the destination already exists.
 *
 * Uses renameat2(2) with RENAME_NOREPLACE (Linux 3.15+).
 *
 * Exit codes:
 *   0  success
 *   1  rename failed (reason on stderr)
 *   2  wrong number of arguments
 */

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/syscall.h>

#ifndef RENAME_NOREPLACE
#define RENAME_NOREPLACE (1 << 0)
#endif

int main(int argc, char *argv[]) {
	if (argc != 3) {
		fprintf(stderr, "usage: mv-sync <src> <dst>\n");
		return 2;
	}

	long ret = syscall(SYS_renameat2,
		AT_FDCWD, argv[1],
		AT_FDCWD, argv[2],
		RENAME_NOREPLACE);

	if (ret != 0) {
		fprintf(stderr, "mv-sync: rename \"%s\" -> \"%s\": %s\n",
			argv[1], argv[2], strerror(errno));
		return 1;
	}

	return 0;
}