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31 Libpcap and Ring Based Poll Mode Drivers
32 ========================================
34 In addition to Poll Mode Drivers (PMDs) for physical and virtual hardware,
35 the DPDK also includes two pure-software PMDs. These two drivers are:
37 * A libpcap -based PMD (librte_pmd_pcap) that reads and writes packets using libpcap,
38 - both from files on disk, as well as from physical NIC devices using standard Linux kernel drivers.
40 * A ring-based PMD (librte_pmd_ring) that allows a set of software FIFOs (that is, rte_ring)
41 to be accessed using the PMD APIs, as though they were physical NICs.
45 The libpcap -based PMD is disabled by default in the build configuration files,
46 owing to an external dependency on the libpcap development files which must be installed on the board.
47 Once the libpcap development files are installed,
48 the library can be enabled by setting CONFIG_RTE_LIBRTE_PMD_PCAP=y and recompiling the DPDK.
50 Using the Drivers from the EAL Command Line
51 -------------------------------------------
53 For ease of use, the DPDK EAL also has been extended to allow pseudo-Ethernet devices,
54 using one or more of these drivers,
55 to be created at application startup time during EAL initialization.
57 To do so, the --vdev= parameter must be passed to the EAL.
58 This takes take options to allow ring and pcap-based Ethernet to be allocated and used transparently by the application.
59 This can be used, for example, for testing on a virtual machine where there are no Ethernet ports.
64 Pcap-based devices can be created using the virtual device --vdev option.
65 The device name must start with the net_pcap prefix followed by numbers or letters.
66 The name is unique for each device. Each device can have multiple stream options and multiple devices can be used.
67 Multiple device definitions can be arranged using multiple --vdev.
68 Device name and stream options must be separated by commas as shown below:
70 .. code-block:: console
72 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
73 --vdev 'net_pcap0,stream_opt0=..,stream_opt1=..' \
74 --vdev='net_pcap1,stream_opt0=..'
79 Multiple ways of stream definitions can be assessed and combined as long as the following two rules are respected:
81 * A device is provided with two different streams - reception and transmission.
83 * A device is provided with one network interface name used for reading and writing packets.
85 The different stream types are:
87 * rx_pcap: Defines a reception stream based on a pcap file.
88 The driver reads each packet within the given pcap file as if it was receiving it from the wire.
89 The value is a path to a valid pcap file.
91 rx_pcap=/path/to/file.pcap
93 * tx_pcap: Defines a transmission stream based on a pcap file.
94 The driver writes each received packet to the given pcap file.
95 The value is a path to a pcap file.
96 The file is overwritten if it already exists and it is created if it does not.
98 tx_pcap=/path/to/file.pcap
100 * rx_iface: Defines a reception stream based on a network interface name.
101 The driver reads packets coming from the given interface using the Linux kernel driver for that interface.
102 The value is an interface name.
106 * tx_iface: Defines a transmission stream based on a network interface name.
107 The driver sends packets to the given interface using the Linux kernel driver for that interface.
108 The value is an interface name.
112 * iface: Defines a device mapping a network interface.
113 The driver both reads and writes packets from and to the given interface.
114 The value is an interface name.
121 Read packets from one pcap file and write them to another:
123 .. code-block:: console
125 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
126 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
127 -- --port-topology=chained
129 Read packets from a network interface and write them to a pcap file:
131 .. code-block:: console
133 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
134 --vdev 'net_pcap0,rx_iface=eth0,tx_pcap=file_tx.pcap' \
135 -- --port-topology=chained
137 Read packets from a pcap file and write them to a network interface:
139 .. code-block:: console
141 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
142 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_iface=eth1' \
143 -- --port-topology=chained
145 Forward packets through two network interfaces:
147 .. code-block:: console
149 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
150 --vdev 'net_pcap0,iface=eth0' --vdev='net_pcap1;iface=eth1'
152 Using libpcap-based PMD with the testpmd Application
153 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
155 One of the first things that testpmd does before starting to forward packets is to flush the RX streams
156 by reading the first 512 packets on every RX stream and discarding them.
157 When using a libpcap-based PMD this behavior can be turned off using the following command line option:
159 .. code-block:: console
163 It is also available in the runtime command line:
165 .. code-block:: console
169 It is useful for the case where the rx_pcap is being used and no packets are meant to be discarded.
170 Otherwise, the first 512 packets from the input pcap file will be discarded by the RX flushing operation.
172 .. code-block:: console
174 $RTE_TARGET/app/testpmd -l 0-3 -n 4 \
175 --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
176 -- --port-topology=chained --no-flush-rx
182 To run a DPDK application on a machine without any Ethernet devices, a pair of ring-based rte_ethdevs can be used as below.
183 The device names passed to the --vdev option must start with net_ring and take no additional parameters.
184 Multiple devices may be specified, separated by commas.
186 .. code-block:: console
188 ./testpmd -l 1-3 -n 4 --vdev=net_ring0 --vdev=net_ring1 -- -i
189 EAL: Detected lcore 1 as core 1 on socket 0
192 Interactive-mode selected
193 Configuring Port 0 (socket 0)
194 Configuring Port 1 (socket 0)
195 Checking link statuses...
196 Port 0 Link Up - speed 10000 Mbps - full-duplex
197 Port 1 Link Up - speed 10000 Mbps - full-duplex
200 testpmd> start tx_first
201 io packet forwarding - CRC stripping disabled - packets/burst=16
202 nb forwarding cores=1 - nb forwarding ports=2
203 RX queues=1 - RX desc=128 - RX free threshold=0
204 RX threshold registers: pthresh=8 hthresh=8 wthresh=4
205 TX queues=1 - TX desc=512 - TX free threshold=0
206 TX threshold registers: pthresh=36 hthresh=0 wthresh=0
207 TX RS bit threshold=0 - TXQ flags=0x0
210 Telling cores to stop...
211 Waiting for lcores to finish...
213 .. image:: img/forward_stats.*
215 .. code-block:: console
217 +++++++++++++++ Accumulated forward statistics for allports++++++++++
218 RX-packets: 462384736 RX-dropped: 0 RX-total: 462384736
219 TX-packets: 462384768 TX-dropped: 0 TX-total: 462384768
220 +++++++++++++++++++++++++++++++++++++++++++++++++++++
225 Using the Poll Mode Driver from an Application
226 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
228 Both drivers can provide similar APIs to allow the user to create a PMD, that is,
229 rte_ethdev structure, instances at run-time in the end-application,
230 for example, using rte_eth_from_rings() or rte_eth_from_pcaps() APIs.
231 For the rings-based PMD, this functionality could be used, for example,
232 to allow data exchange between cores using rings to be done in exactly the
233 same way as sending or receiving packets from an Ethernet device.
234 For the libpcap-based PMD, it allows an application to open one or more pcap files
235 and use these as a source of packet input to the application.
240 To create two pseudo-Ethernet ports where all traffic sent to a port is looped back
241 for reception on the same port (error handling omitted for clarity):
245 #define RING_SIZE 256
249 struct rte_ring *ring[NUM_RINGS];
252 ring[0] = rte_ring_create("R0", RING_SIZE, SOCKET0, RING_F_SP_ENQ|RING_F_SC_DEQ);
253 ring[1] = rte_ring_create("R1", RING_SIZE, SOCKET0, RING_F_SP_ENQ|RING_F_SC_DEQ);
255 /* create two ethdev's */
257 port0 = rte_eth_from_rings("net_ring0", ring, NUM_RINGS, ring, NUM_RINGS, SOCKET0);
258 port1 = rte_eth_from_rings("net_ring1", ring, NUM_RINGS, ring, NUM_RINGS, SOCKET0);
261 To create two pseudo-Ethernet ports where the traffic is switched between them,
262 that is, traffic sent to port 0 is read back from port 1 and vice-versa,
263 the final two lines could be changed as below:
267 port0 = rte_eth_from_rings("net_ring0", &ring[0], 1, &ring[1], 1, SOCKET0);
268 port1 = rte_eth_from_rings("net_ring1", &ring[1], 1, &ring[0], 1, SOCKET0);
270 This type of configuration could be useful in a pipeline model, for example,
271 where one may want to have inter-core communication using pseudo Ethernet devices rather than raw rings,
272 for reasons of API consistency.
274 Enqueuing and dequeuing items from an rte_ring using the rings-based PMD may be slower than using the native rings API.
275 This is because DPDK Ethernet drivers make use of function pointers to call the appropriate enqueue or dequeue functions,
276 while the rte_ring specific functions are direct function calls in the code and are often inlined by the compiler.
278 Once an ethdev has been created, for either a ring or a pcap-based PMD,
279 it should be configured and started in the same way as a regular Ethernet device, that is,
280 by calling rte_eth_dev_configure() to set the number of receive and transmit queues,
281 then calling rte_eth_rx_queue_setup() / tx_queue_setup() for each of those queues and
282 finally calling rte_eth_dev_start() to allow transmission and reception of packets to begin.