and so on between different entities in the system.
Message buffers may also use their buffer pointers to point to other message buffer data sections or other structures.
-Figure 8 and Figure 9 show some of these scenarios.
+:numref:`figure_mbuf1` and :numref:`figure_mbuf2` show some of these scenarios.
-.. _pg_figure_8:
+.. _figure_mbuf1:
-**Figure 8. An mbuf with One Segment**
+.. figure:: img/mbuf1.*
-.. image22_png has been replaced
+ An mbuf with One Segment
-|mbuf1|
-.. _pg_figure_9:
+.. _figure_mbuf2:
-**Figure 9. An mbuf with Three Segments**
+.. figure:: img/mbuf2.*
-.. image23_png has been replaced
+ An mbuf with Three Segments
-|mbuf2|
The Buffer Manager implements a fairly standard set of buffer access functions to manipulate network packets.
For chained buffers, only the first mbuf of the chain stores this meta information.
+For instance, this is the case on RX side for the IEEE1588 packet
+timestamp mechanism, the VLAN tagging and the IP checksum computation.
+
+On TX side, it is also possible for an application to delegate some
+processing to the hardware if it supports it. For instance, the
+PKT_TX_IP_CKSUM flag allows to offload the computation of the IPv4
+checksum.
+
+The following examples explain how to configure different TX offloads on
+a vxlan-encapsulated tcp packet:
+``out_eth/out_ip/out_udp/vxlan/in_eth/in_ip/in_tcp/payload``
+
+- calculate checksum of out_ip::
+
+ mb->l2_len = len(out_eth)
+ mb->l3_len = len(out_ip)
+ mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CSUM
+ set out_ip checksum to 0 in the packet
+
+ This is supported on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM.
+
+- calculate checksum of out_ip and out_udp::
+
+ mb->l2_len = len(out_eth)
+ mb->l3_len = len(out_ip)
+ mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CSUM | PKT_TX_UDP_CKSUM
+ set out_ip checksum to 0 in the packet
+ set out_udp checksum to pseudo header using rte_ipv4_phdr_cksum()
+
+ This is supported on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM
+ and DEV_TX_OFFLOAD_UDP_CKSUM.
+
+- calculate checksum of in_ip::
+
+ mb->l2_len = len(out_eth + out_ip + out_udp + vxlan + in_eth)
+ mb->l3_len = len(in_ip)
+ mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CSUM
+ set in_ip checksum to 0 in the packet
+
+ This is similar to case 1), but l2_len is different. It is supported
+ on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM.
+ Note that it can only work if outer L4 checksum is 0.
+
+- calculate checksum of in_ip and in_tcp::
+
+ mb->l2_len = len(out_eth + out_ip + out_udp + vxlan + in_eth)
+ mb->l3_len = len(in_ip)
+ mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CSUM | PKT_TX_TCP_CKSUM
+ set in_ip checksum to 0 in the packet
+ set in_tcp checksum to pseudo header using rte_ipv4_phdr_cksum()
+
+ This is similar to case 2), but l2_len is different. It is supported
+ on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM and
+ DEV_TX_OFFLOAD_TCP_CKSUM.
+ Note that it can only work if outer L4 checksum is 0.
+
+- segment inner TCP::
+
+ mb->l2_len = len(out_eth + out_ip + out_udp + vxlan + in_eth)
+ mb->l3_len = len(in_ip)
+ mb->l4_len = len(in_tcp)
+ mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CKSUM | PKT_TX_TCP_CKSUM |
+ PKT_TX_TCP_SEG;
+ set in_ip checksum to 0 in the packet
+ set in_tcp checksum to pseudo header without including the IP
+ payload length using rte_ipv4_phdr_cksum()
+
+ This is supported on hardware advertising DEV_TX_OFFLOAD_TCP_TSO.
+ Note that it can only work if outer L4 checksum is 0.
+
+- calculate checksum of out_ip, in_ip, in_tcp::
+
+ mb->outer_l2_len = len(out_eth)
+ mb->outer_l3_len = len(out_ip)
+ mb->l2_len = len(out_udp + vxlan + in_eth)
+ mb->l3_len = len(in_ip)
+ mb->ol_flags |= PKT_TX_OUTER_IPV4 | PKT_TX_OUTER_IP_CKSUM | \
+ PKT_TX_IP_CKSUM | PKT_TX_TCP_CKSUM;
+ set out_ip checksum to 0 in the packet
+ set in_ip checksum to 0 in the packet
+ set in_tcp checksum to pseudo header using rte_ipv4_phdr_cksum()
+
+ This is supported on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM,
+ DEV_TX_OFFLOAD_UDP_CKSUM and DEV_TX_OFFLOAD_OUTER_IPV4_CKSUM.
+
+The list of flags and their precise meaning is described in the mbuf API
+documentation (rte_mbuf.h). Also refer to the testpmd source code
+(specifically the csumonly.c file) for details.
+
Direct and Indirect Buffers
---------------------------
---------
All networking application should use mbufs to transport network packets.
-
-.. |mbuf1| image:: img/mbuf1.*
-
-.. |mbuf2| image:: img/mbuf2.*