Hack mongo-c-driver to make it usable in seastar under async context. And thus we can use mongo-c-driver and mongo-cxx-driver.
Before use it, you should modify file mongoc-socket.c of mongo-c-driver
static bool
_mongoc_socket_wait (mongoc_socket_t *sock, /* IN */
int events, /* IN */
int64_t expire_at) /* IN */
to
bool
_mongoc_socket_wait (mongoc_socket_t *sock, /* IN */
int events, /* IN */
int64_t expire_at) /* IN */