SV *
my_xs_func(p_struct, len)
        void *p_struct;
        IV len
    PREINIT:
        int bytes_read;
        char *tmp_buffer;
    PPCODE:
        tmp_buffer = (char *)malloc(len + 1); // + 1 for NULL
        if (tmp_buffer == NULL)
            XSRETURN_UNDEF;

        bytes_read = my_func(p_struct, tmp_buffer, len);
 
        // need to NULL-terminate the buffer
        tmp_buffer[bytes_read] = '\0';

        XPUSHs(sv_2mortal(newSVpv(tmp_buffer, bytes_read)));

        free(tmp_buffer);