dirCreateDirPosix

fn dirCreateDirPosix(userdata: ?*anyopaque, dir: Dir, sub_path: []const u8, permissions: Dir.Permissions) Dir.CreateDirError!void {
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    _ = t;

    var path_buffer: [posix.PATH_MAX]u8 = undefined;
    const sub_path_posix = try pathToPosix(sub_path, &path_buffer);

    const syscall: Syscall = try .start();
    while (true) {
        switch (posix.errno(posix.system.mkdirat(dir.handle, sub_path_posix, permissions.toMode()))) {
            .SUCCESS => {
                syscall.finish();
                return;
            },
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            .ACCES => return syscall.fail(error.AccessDenied),
            .PERM => return syscall.fail(error.PermissionDenied),
            .DQUOT => return syscall.fail(error.DiskQuota),
            .EXIST => return syscall.fail(error.PathAlreadyExists),
            .LOOP => return syscall.fail(error.SymLinkLoop),
            .MLINK => return syscall.fail(error.LinkQuotaExceeded),
            .NAMETOOLONG => return syscall.fail(error.NameTooLong),
            .NOENT => return syscall.fail(error.FileNotFound),
            .NOMEM => return syscall.fail(error.SystemResources),
            .NOSPC => return syscall.fail(error.NoSpaceLeft),
            .NOTDIR => return syscall.fail(error.NotDir),
            .ROFS => return syscall.fail(error.ReadOnlyFileSystem),
            // dragonfly: when dir_fd is unlinked from filesystem
            .NOTCONN => return syscall.fail(error.FileNotFound),
            .ILSEQ => return syscall.fail(error.BadPathName),
            .BADF => |err| return syscall.errnoBug(err), // File descriptor used after closed.
            .FAULT => |err| return syscall.errnoBug(err),
            else => |err| return syscall.unexpectedErrno(err),
        }
    }
}