1 .. SPDX-License-Identifier: BSD-3-Clause
2 Copyright(c) 2010-2015 Intel Corporation.
4 Libpcap and Ring Based Poll Mode Drivers
5 ========================================
7 In addition to Poll Mode Drivers (PMDs) for physical and virtual hardware,
8 the DPDK also includes pure-software PMDs, two of these drivers are:
10 * A libpcap -based PMD (librte_pmd_pcap) that reads and writes packets using libpcap,
11 - both from files on disk, as well as from physical NIC devices using standard Linux kernel drivers.
13 * A ring-based PMD (librte_pmd_ring) that allows a set of software FIFOs (that is, rte_ring)
14 to be accessed using the PMD APIs, as though they were physical NICs.
18 The libpcap -based PMD is disabled by default in the build configuration files,
19 owing to an external dependency on the libpcap development files which must be installed on the board.
20 Once the libpcap development files are installed,
21 the library can be enabled by setting CONFIG_RTE_LIBRTE_PMD_PCAP=y and recompiling the DPDK.
23 Using the Drivers from the EAL Command Line
24 -------------------------------------------
26 For ease of use, the DPDK EAL also has been extended to allow pseudo-Ethernet devices,
27 using one or more of these drivers,
28 to be created at application startup time during EAL initialization.
30 To do so, the --vdev= parameter must be passed to the EAL.
31 This takes take options to allow ring and pcap-based Ethernet to be allocated and used transparently by the application.
32 This can be used, for example, for testing on a virtual machine where there are no Ethernet ports.
37 Pcap-based devices can be created using the virtual device --vdev option.
38 The device name must start with the net_pcap prefix followed by numbers or letters.
39 The name is unique for each device. Each device can have multiple stream options and multiple devices can be used.
40 Multiple device definitions can be arranged using multiple --vdev.
41 Device name and stream options must be separated by commas as shown below:
43 .. code-block:: console
45 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
46 --vdev 'net_pcap0,stream_opt0=..,stream_opt1=..' \
47 --vdev='net_pcap1,stream_opt0=..'
52 Multiple ways of stream definitions can be assessed and combined as long as the following two rules are respected:
54 * A device is provided with two different streams - reception and transmission.
56 * A device is provided with one network interface name used for reading and writing packets.
58 The different stream types are:
60 * rx_pcap: Defines a reception stream based on a pcap file.
61 The driver reads each packet within the given pcap file as if it was receiving it from the wire.
62 The value is a path to a valid pcap file.
64 rx_pcap=/path/to/file.pcap
66 * tx_pcap: Defines a transmission stream based on a pcap file.
67 The driver writes each received packet to the given pcap file.
68 The value is a path to a pcap file.
69 The file is overwritten if it already exists and it is created if it does not.
71 tx_pcap=/path/to/file.pcap
73 * rx_iface: Defines a reception stream based on a network interface name.
74 The driver reads packets from the given interface using the Linux kernel driver for that interface.
75 The driver captures both the incoming and outgoing packets on that interface.
76 The value is an interface name.
80 * rx_iface_in: Defines a reception stream based on a network interface name.
81 The driver reads packets from the given interface using the Linux kernel driver for that interface.
82 The driver captures only the incoming packets on that interface.
83 The value is an interface name.
87 * tx_iface: Defines a transmission stream based on a network interface name.
88 The driver sends packets to the given interface using the Linux kernel driver for that interface.
89 The value is an interface name.
93 * iface: Defines a device mapping a network interface.
94 The driver both reads and writes packets from and to the given interface.
95 The value is an interface name.
102 Read packets from one pcap file and write them to another:
104 .. code-block:: console
106 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
107 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
108 -- --port-topology=chained
110 Read packets from a network interface and write them to a pcap file:
112 .. code-block:: console
114 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
115 --vdev 'net_pcap0,rx_iface=eth0,tx_pcap=file_tx.pcap' \
116 -- --port-topology=chained
118 Read packets from a pcap file and write them to a network interface:
120 .. code-block:: console
122 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
123 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_iface=eth1' \
124 -- --port-topology=chained
126 Forward packets through two network interfaces:
128 .. code-block:: console
130 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
131 --vdev 'net_pcap0,iface=eth0' --vdev='net_pcap1;iface=eth1'
133 Enable 2 tx queues on a network interface:
135 .. code-block:: console
137 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
138 --vdev 'net_pcap0,rx_iface=eth1,tx_iface=eth1,tx_iface=eth1' \
141 Read only incoming packets from a network interface and write them back to the same network interface:
143 .. code-block:: console
145 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
146 --vdev 'net_pcap0,rx_iface_in=eth1,tx_iface=eth1'
148 Using libpcap-based PMD with the testpmd Application
149 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
151 One of the first things that testpmd does before starting to forward packets is to flush the RX streams
152 by reading the first 512 packets on every RX stream and discarding them.
153 When using a libpcap-based PMD this behavior can be turned off using the following command line option:
155 .. code-block:: console
159 It is also available in the runtime command line:
161 .. code-block:: console
165 It is useful for the case where the rx_pcap is being used and no packets are meant to be discarded.
166 Otherwise, the first 512 packets from the input pcap file will be discarded by the RX flushing operation.
168 .. code-block:: console
170 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
171 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
172 -- --port-topology=chained --no-flush-rx
176 The network interface provided to the PMD should be up. The PMD will return
177 an error if interface is down, and the PMD itself won't change the status
178 of the external network interface.
184 To run a DPDK application on a machine without any Ethernet devices, a pair of ring-based rte_ethdevs can be used as below.
185 The device names passed to the --vdev option must start with net_ring and take no additional parameters.
186 Multiple devices may be specified, separated by commas.
188 .. code-block:: console
190 ./testpmd -l 1-3 -n 4 --vdev=net_ring0 --vdev=net_ring1 -- -i
191 EAL: Detected lcore 1 as core 1 on socket 0
194 Interactive-mode selected
195 Configuring Port 0 (socket 0)
196 Configuring Port 1 (socket 0)
197 Checking link statuses...
198 Port 0 Link Up - speed 10000 Mbps - full-duplex
199 Port 1 Link Up - speed 10000 Mbps - full-duplex
202 testpmd> start tx_first
203 io packet forwarding - CRC stripping disabled - packets/burst=16
204 nb forwarding cores=1 - nb forwarding ports=2
205 RX queues=1 - RX desc=128 - RX free threshold=0
206 RX threshold registers: pthresh=8 hthresh=8 wthresh=4
207 TX queues=1 - TX desc=512 - TX free threshold=0
208 TX threshold registers: pthresh=36 hthresh=0 wthresh=0
209 TX RS bit threshold=0 - TXQ flags=0x0
212 Telling cores to stop...
213 Waiting for lcores to finish...
215 .. image:: img/forward_stats.*
217 .. code-block:: console
219 +++++++++++++++ Accumulated forward statistics for allports++++++++++
220 RX-packets: 462384736 RX-dropped: 0 RX-total: 462384736
221 TX-packets: 462384768 TX-dropped: 0 TX-total: 462384768
222 +++++++++++++++++++++++++++++++++++++++++++++++++++++
227 Using the Poll Mode Driver from an Application
228 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
230 Both drivers can provide similar APIs to allow the user to create a PMD, that is,
231 rte_ethdev structure, instances at run-time in the end-application,
232 for example, using rte_eth_from_rings() or rte_eth_from_pcaps() APIs.
233 For the rings-based PMD, this functionality could be used, for example,
234 to allow data exchange between cores using rings to be done in exactly the
235 same way as sending or receiving packets from an Ethernet device.
236 For the libpcap-based PMD, it allows an application to open one or more pcap files
237 and use these as a source of packet input to the application.
242 To create two pseudo-Ethernet ports where all traffic sent to a port is looped back
243 for reception on the same port (error handling omitted for clarity):
247 #define RING_SIZE 256
251 struct rte_ring *ring[NUM_RINGS];
254 ring[0] = rte_ring_create("R0", RING_SIZE, SOCKET0, RING_F_SP_ENQ|RING_F_SC_DEQ);
255 ring[1] = rte_ring_create("R1", RING_SIZE, SOCKET0, RING_F_SP_ENQ|RING_F_SC_DEQ);
257 /* create two ethdev's */
259 port0 = rte_eth_from_rings("net_ring0", ring, NUM_RINGS, ring, NUM_RINGS, SOCKET0);
260 port1 = rte_eth_from_rings("net_ring1", ring, NUM_RINGS, ring, NUM_RINGS, SOCKET0);
263 To create two pseudo-Ethernet ports where the traffic is switched between them,
264 that is, traffic sent to port 0 is read back from port 1 and vice-versa,
265 the final two lines could be changed as below:
269 port0 = rte_eth_from_rings("net_ring0", &ring[0], 1, &ring[1], 1, SOCKET0);
270 port1 = rte_eth_from_rings("net_ring1", &ring[1], 1, &ring[0], 1, SOCKET0);
272 This type of configuration could be useful in a pipeline model, for example,
273 where one may want to have inter-core communication using pseudo Ethernet devices rather than raw rings,
274 for reasons of API consistency.
276 Enqueuing and dequeuing items from an rte_ring using the rings-based PMD may be slower than using the native rings API.
277 This is because DPDK Ethernet drivers make use of function pointers to call the appropriate enqueue or dequeue functions,
278 while the rte_ring specific functions are direct function calls in the code and are often inlined by the compiler.
280 Once an ethdev has been created, for either a ring or a pcap-based PMD,
281 it should be configured and started in the same way as a regular Ethernet device, that is,
282 by calling rte_eth_dev_configure() to set the number of receive and transmit queues,
283 then calling rte_eth_rx_queue_setup() / tx_queue_setup() for each of those queues and
284 finally calling rte_eth_dev_start() to allow transmission and reception of packets to begin.