VPP provides RFC5424 syslog protocol logging, which is used to transport event messages across network. VPP currently suports UDP transport based on RFC5426.

The syslog message has the following format:

header
structured data
free-form message

The header contains, priority, version, timestamp, hostname, application, process id and message id. It is followed by structured data, which provides a mechanism to express event data in easily parsable format. Structured data can contain zero, one or multiple structured data elements. Structured data element contains name-value pairs. Structured data can by followed by free-form message.

Following example explains how to use the internal APIs to genrate syslog message:

#include <vnet/syslog/syslog.h>
...
syslog_msg_t syslog_msg;
/* Check if syslog logging is enabled */
if (!syslog_is_enabled ())
  return;
/* Severity filer test */
if (syslog_severity_filter_block (severity))
  return;
/* Initialize syslog message header */
syslog_msg_init (&syslog_msg, facility, severity, "NAT", "SADD");
/* Create structured data element */
syslog_msg_sd_init (&syslog_msg, "nsess");
/* Add structured data element parameters (name-value pairs) */
syslog_msg_add_sd_param (&syslog_msg, "SSUBIX", "%d", ssubix);
syslog_msg_add_sd_param (&syslog_msg, "SVLAN", "%d", svlan);
syslog_msg_add_sd_param (&syslog_msg, "IATYP", "IPv4");
syslog_msg_add_sd_param (&syslog_msg, "ISADDR", "%U",
                         format_ip4_address, isaddr);
syslog_msg_add_sd_param (&syslog_msg, "ISPORT", "%d", isport);
syslog_msg_add_sd_param (&syslog_msg, "XATYP", "IPv4");
syslog_msg_add_sd_param (&syslog_msg, "XSADDR", "%U",
                         format_ip4_address, xsaddr);
syslog_msg_add_sd_param (&syslog_msg, "XSPORT", "%d", xsport);
syslog_msg_add_sd_param (&syslog_msg, "PROTO", "%d", proto);
/* Send syslog message */
syslog_msg_send (&syslog_msg);

Example above produces following syslog message: <134>1 2018-11-12T11:25:30.252715Z 172.16.4.1 NAT 5901 SADD [nsess SSUBIX="0" SVLAN="0" IATYP="IPv4" ISADDR="172.16.1.2" ISPORT="6303" XATYP="IPv4" XSADDR="10.0.0.3" XSPORT="16253" PROTO="6"]

To add free-form message use:

syslog_msg_add_msg (&syslog_msg, "event log entry");