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.
99 Runtime Config Options
100 ^^^^^^^^^^^^^^^^^^^^^^
102 - Use PCAP interface physical MAC
104 In case ``iface=`` configuration is set, user may want to use the selected interface's physical MAC
105 address. This can be done with a ``devarg`` ``phy_mac``, for example::
107 --vdev 'net_pcap0,iface=eth0,phy_mac=1'
109 - Use the RX PCAP file to infinitely receive packets
111 In case ``rx_pcap=`` configuration is set, user may want to use the selected PCAP file for rudimental
112 performance testing. This can be done with a ``devarg`` ``infinite_rx``, for example::
114 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,infinite_rx=1'
116 When this mode is used, it is recommended to drop all packets on transmit by not providing a tx_pcap or tx_iface.
118 This option is device wide, so all queues on a device will either have this enabled or disabled.
119 This option should only be provided once per device.
121 - Drop all packets on transmit
123 The user may want to drop all packets on tx for a device. This can be done by not providing a tx_pcap or tx_iface, for example::
125 --vdev 'net_pcap0,rx_pcap=file_rx.pcap'
127 In this case, one tx drop queue is created for each rxq on that device.
132 Read packets from one pcap file and write them to another:
134 .. code-block:: console
136 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
137 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
138 -- --port-topology=chained
140 Read packets from a network interface and write them to a pcap file:
142 .. code-block:: console
144 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
145 --vdev 'net_pcap0,rx_iface=eth0,tx_pcap=file_tx.pcap' \
146 -- --port-topology=chained
148 Read packets from a pcap file and write them to a network interface:
150 .. code-block:: console
152 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
153 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_iface=eth1' \
154 -- --port-topology=chained
156 Forward packets through two network interfaces:
158 .. code-block:: console
160 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
161 --vdev 'net_pcap0,iface=eth0' --vdev='net_pcap1;iface=eth1'
163 Enable 2 tx queues on a network interface:
165 .. code-block:: console
167 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
168 --vdev 'net_pcap0,rx_iface=eth1,tx_iface=eth1,tx_iface=eth1' \
171 Read only incoming packets from a network interface and write them back to the same network interface:
173 .. code-block:: console
175 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
176 --vdev 'net_pcap0,rx_iface_in=eth1,tx_iface=eth1'
178 Using libpcap-based PMD with the testpmd Application
179 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
181 One of the first things that testpmd does before starting to forward packets is to flush the RX streams
182 by reading the first 512 packets on every RX stream and discarding them.
183 When using a libpcap-based PMD this behavior can be turned off using the following command line option:
185 .. code-block:: console
189 It is also available in the runtime command line:
191 .. code-block:: console
195 It is useful for the case where the rx_pcap is being used and no packets are meant to be discarded.
196 Otherwise, the first 512 packets from the input pcap file will be discarded by the RX flushing operation.
198 .. code-block:: console
200 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
201 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
202 -- --port-topology=chained --no-flush-rx
206 The network interface provided to the PMD should be up. The PMD will return
207 an error if interface is down, and the PMD itself won't change the status
208 of the external network interface.
214 To run a DPDK application on a machine without any Ethernet devices, a pair of ring-based rte_ethdevs can be used as below.
215 The device names passed to the --vdev option must start with net_ring and take no additional parameters.
216 Multiple devices may be specified, separated by commas.
218 .. code-block:: console
220 ./testpmd -l 1-3 -n 4 --vdev=net_ring0 --vdev=net_ring1 -- -i
221 EAL: Detected lcore 1 as core 1 on socket 0
224 Interactive-mode selected
225 Configuring Port 0 (socket 0)
226 Configuring Port 1 (socket 0)
227 Checking link statuses...
228 Port 0 Link Up - speed 10000 Mbps - full-duplex
229 Port 1 Link Up - speed 10000 Mbps - full-duplex
232 testpmd> start tx_first
233 io packet forwarding - CRC stripping disabled - packets/burst=16
234 nb forwarding cores=1 - nb forwarding ports=2
235 RX queues=1 - RX desc=128 - RX free threshold=0
236 RX threshold registers: pthresh=8 hthresh=8 wthresh=4
237 TX queues=1 - TX desc=512 - TX free threshold=0
238 TX threshold registers: pthresh=36 hthresh=0 wthresh=0
239 TX RS bit threshold=0 - TXQ flags=0x0
242 Telling cores to stop...
243 Waiting for lcores to finish...
245 .. image:: img/forward_stats.*
247 .. code-block:: console
249 +++++++++++++++ Accumulated forward statistics for allports++++++++++
250 RX-packets: 462384736 RX-dropped: 0 RX-total: 462384736
251 TX-packets: 462384768 TX-dropped: 0 TX-total: 462384768
252 +++++++++++++++++++++++++++++++++++++++++++++++++++++
257 Using the Poll Mode Driver from an Application
258 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
260 Both drivers can provide similar APIs to allow the user to create a PMD, that is,
261 rte_ethdev structure, instances at run-time in the end-application,
262 for example, using rte_eth_from_rings() or rte_eth_from_pcaps() APIs.
263 For the rings-based PMD, this functionality could be used, for example,
264 to allow data exchange between cores using rings to be done in exactly the
265 same way as sending or receiving packets from an Ethernet device.
266 For the libpcap-based PMD, it allows an application to open one or more pcap files
267 and use these as a source of packet input to the application.
272 To create two pseudo-Ethernet ports where all traffic sent to a port is looped back
273 for reception on the same port (error handling omitted for clarity):
277 #define RING_SIZE 256
281 struct rte_ring *ring[NUM_RINGS];
284 ring[0] = rte_ring_create("R0", RING_SIZE, SOCKET0, RING_F_SP_ENQ|RING_F_SC_DEQ);
285 ring[1] = rte_ring_create("R1", RING_SIZE, SOCKET0, RING_F_SP_ENQ|RING_F_SC_DEQ);
287 /* create two ethdev's */
289 port0 = rte_eth_from_rings("net_ring0", ring, NUM_RINGS, ring, NUM_RINGS, SOCKET0);
290 port1 = rte_eth_from_rings("net_ring1", ring, NUM_RINGS, ring, NUM_RINGS, SOCKET0);
293 To create two pseudo-Ethernet ports where the traffic is switched between them,
294 that is, traffic sent to port 0 is read back from port 1 and vice-versa,
295 the final two lines could be changed as below:
299 port0 = rte_eth_from_rings("net_ring0", &ring[0], 1, &ring[1], 1, SOCKET0);
300 port1 = rte_eth_from_rings("net_ring1", &ring[1], 1, &ring[0], 1, SOCKET0);
302 This type of configuration could be useful in a pipeline model, for example,
303 where one may want to have inter-core communication using pseudo Ethernet devices rather than raw rings,
304 for reasons of API consistency.
306 Enqueuing and dequeuing items from an rte_ring using the rings-based PMD may be slower than using the native rings API.
307 This is because DPDK Ethernet drivers make use of function pointers to call the appropriate enqueue or dequeue functions,
308 while the rte_ring specific functions are direct function calls in the code and are often inlined by the compiler.
310 Once an ethdev has been created, for either a ring or a pcap-based PMD,
311 it should be configured and started in the same way as a regular Ethernet device, that is,
312 by calling rte_eth_dev_configure() to set the number of receive and transmit queues,
313 then calling rte_eth_rx_queue_setup() / tx_queue_setup() for each of those queues and
314 finally calling rte_eth_dev_start() to allow transmission and reception of packets to begin.