mbuf data is 1400 bytes but the most common (?) use, Ethernet II frames, allow for 1518 bytes

[Nicolson Ken (ニコルソン ケン)]

Hi all,

Looking at sending Ethernet packets over a DPDK connection, I see that an Ethernet Type II frame has 1518 max, but mbuf's data block is 1400 bytes.

Is this what the headroom and tailroom are for? I see example code that uses the headroom for the MAC Header, but what is the preferred way of copying a 1518 Ethernet packet into an mbuf? Should I use rte_pktmbuf_append() to reserve the extra bytes, or is there a better way?

Thanks,
Ken