if (log && ((log_size + sizeof(struct log_head)) < size)) {
struct log_head *start = _log;
struct log_head *end = ((void*) _log) + size;
if (log && ((log_size + sizeof(struct log_head)) < size)) {
struct log_head *start = _log;
struct log_head *end = ((void*) _log) + size;