Kernel/LibC: Implement rename{,at}

userspace/libraries/LibC/include/sys/syscall.h

@@ -14,6 +14,7 @@ __BEGIN_DECLS
 	O(SYS_OPENAT,			openat)			\
 	O(SYS_SEEK,				seek)			\
 	O(SYS_TELL,				tell)			\
+	O(SYS_RENAMEAT,			renameat)		\
 	O(SYS_TCGETATTR,		tcgetattr)		\
 	O(SYS_TCSETATTR,		tcsetattr)		\
 	O(SYS_FORK,				fork)			\

userspace/libraries/LibC/stdio.cpp

@@ -820,56 +820,12 @@ int remove(const char* path)
 
 int rename(const char* old, const char* _new)
 {
-	struct stat st;
-	if (lstat(old, &st) == -1)
-		return -1;
+	return renameat(AT_FDCWD, old, AT_FDCWD, _new);
+}
 
-	if (!S_ISREG(st.st_mode))
-	{
-		errno = ENOTSUP;
-		return -1;
-	}
-
-	if (unlink(_new) == -1 && errno != ENOENT)
-		return -1;
-
-	int old_fd = open(old, O_RDWR);
-	int new_fd = open(_new, O_RDWR | O_CREAT | O_EXCL, st.st_mode);
-	if (old_fd == -1 || new_fd == -1)
-		goto error;
-
-	for (;;)
-	{
-		char buffer[512];
-		ssize_t nread = read(old_fd, buffer, sizeof(buffer));
-		if (nread == -1)
-		{
-			unlink(_new);
-			goto error;
-		}
-		if (nread == 0)
-			break;
-
-		if (write(new_fd, buffer, nread) != nread)
-		{
-			unlink(_new);
-			goto error;
-		}
-	}
-
-	close(new_fd);
-	close(old_fd);
-
-	unlink(old);
-
-	return 0;
-
-error:
-	if (old_fd != -1)
-		close(old_fd);
-	if (new_fd != -1)
-		close(new_fd);
-	return -1;
+int renameat(int oldfd, const char* old, int newfd, const char* _new)
+{
+	return syscall(SYS_RENAMEAT, oldfd, old, newfd, _new);
 }
 
 void rewind(FILE* file)