45. Packet Capture Library
The DPDK pdump library provides a framework for packet capturing in DPDK.
The library does the complete copy of the Rx and Tx mbufs to a new mempool and
hence it slows down the performance of the applications, so it is recommended
to use this library for debugging purposes.
The library uses a generic multi process channel to facilitate communication between primary and secondary process for enabling/disabling packet capture on ports.
The library provides the following APIs to initialize the packet capture framework, to enable or disable the packet capture, and to uninitialize it.
rte_pdump_init(): This API initializes the packet capture framework.rte_pdump_enable(): This API enables the packet capture on a given port and queue.rte_pdump_enable_bpf()This API enables the packet capture on a given port and queue. It also allows setting an optional filter using DPDK BPF interpreter and setting the captured packet length.rte_pdump_enable_by_deviceid(): This API enables the packet capture on a given device id (vdev name or pci address) and queue.rte_pdump_enable_bpf_by_deviceid()This API enables the packet capture on a given device id (vdev name or pci address) and queue. It also allows setting an optional filter using DPDK BPF interpreter and setting the captured packet length.rte_pdump_disable(): This API disables the packet capture on a given port and queue.rte_pdump_disable_by_deviceid(): This API disables the packet capture on a given device id (vdev name or pci address) and queue.rte_pdump_uninit(): This API uninitializes the packet capture framework.
45.1. Operation
The primary process using librte_pdump is responsible for initializing the packet
capture framework. The packet capture framework, as part of its initialization, creates the
multi process channel to facilitate communication with secondary process, so the
secondary process app/pdump tool is responsible for enabling and disabling the packet capture on ports.
45.2. Implementation Details
The library API rte_pdump_init(), initializes the packet capture framework by creating the multi process
channel using rte_mp_action_register() API. The primary process will listen to secondary process requests
to enable or disable the packet capture over the multi process channel.
The library APIs rte_pdump_enable() and rte_pdump_enable_by_deviceid() enables the packet capture.
For the calls to these APIs from secondary process, the library creates the “pdump enable” request and sends
the request to the primary process over the multi process channel. The primary process takes this request
and enables the packet capture by registering the Ethernet RX and TX callbacks for the given port or device_id
and queue combinations. Then the primary process will mirror the packets to the new mempool and enqueue them to
the rte_ring that secondary process have passed to these APIs.
The packet ring supports one of two formats.
The default format enqueues copies of the original packets into the rte_ring.
If the RTE_PDUMP_FLAG_PCAPNG is set, the mbuf data is extended
with header and trailer to match the format of Pcapng enhanced packet block.
The enhanced packet block has meta-data such as the timestamp, port and queue
the packet was captured on.
It is up to the application consuming the packets from the ring
to select the format desired.
The library APIs rte_pdump_disable() and rte_pdump_disable_by_deviceid() disables the packet capture.
For the calls to these APIs from secondary process, the library creates the “pdump disable” request and sends
the request to the primary process over the multi process channel. The primary process takes this request and
disables the packet capture by removing the Ethernet RX and TX callbacks for the given port or device_id and
queue combinations.
The library API rte_pdump_uninit(), uninitializes the packet capture framework by calling rte_mp_action_unregister()
function.
45.3. Use Case: Packet Capturing
The DPDK app/dpdk-dumpcap utility uses this library
to capture packets in DPDK.