Direct Mem Pool vs Indirect mem pool creation

[omer yamac]

Hello,

I need clarification while creating direct/indirect buffers for mbuf. I
couldn't find exact documentation, and I just looked over the fragmentation
test case and saw that two pools were created. One is a
direct pool, and the other is an indirect pool. Here are the methods to
create pools:
direct_pool = rte_pktmbuf_pool_create("FRAG_D_MBUF_POOL",
                          NUM_MBUFS, BURST, 0,
                          RTE_MBUF_DEFAULT_BUF_SIZE,
                          SOCKET_ID_ANY);
indirect_pool = rte_pktmbuf_pool_create("FRAG_I_MBUF_POOL",
                        NUM_MBUFS, BURST, 0,
                        0, SOCKET_ID_ANY)

I couldn't see the exact difference. Just the "data_room_size" parameter is
different. If this parameter is 0, then is the pool indirect?

Thanks all