-.. BSD LICENSE
- Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
- All rights reserved.
-
- Redistribution and use in source and binary forms, with or without
- modification, are permitted provided that the following conditions
- are met:
-
- * Redistributions of source code must retain the above copyright
- notice, this list of conditions and the following disclaimer.
- * Redistributions in binary form must reproduce the above copyright
- notice, this list of conditions and the following disclaimer in
- the documentation and/or other materials provided with the
- distribution.
- * Neither the name of Intel Corporation nor the names of its
- contributors may be used to endorse or promote products derived
- from this software without specific prior written permission.
-
- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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- OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright(c) 2010-2014 Intel Corporation.
.. _Mbuf_Library:
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_indirect_buffer:
+
Direct and Indirect Buffers
---------------------------
If the resulting reference counter is equal to 0, the direct buffer is freed since it is no longer in use.
There are a few things to remember when dealing with indirect buffers.
-First of all, it is not possible to attach an indirect buffer to another indirect buffer.
+First of all, an indirect buffer is never attached to another indirect buffer.
+Attempting to attach buffer A to indirect buffer B that is attached to C, makes rte_pktmbuf_attach() automatically attach A to C, effectively cloning B.
Secondly, for a buffer to become indirect, its reference counter must be equal to 1,
that is, it must not be already referenced by another indirect buffer.
Finally, it is not possible to reattach an indirect buffer to the direct buffer (unless it is detached first).
---------
All networking application should use mbufs to transport network packets.
-
-.. |mbuf1| image:: img/mbuf1.svg
-
-.. |mbuf2| image:: img/mbuf2.svg
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