Detailed Output

The detailed form of output is also the default form. This form groups output into sections headed up by the ingress or egress pipeline being traversed. Each pipeline lists each table that was visited (by number and name), the ovn-northd source file and line number of the code that added the flow, the match expression and priority of the logical flow that was matched, and the actions that were executed.

The execution of OVN logical actions naturally forms a ``control stack’’ that resembles that of a program in conventional programming languages such as C or Java. Because the next action that calls into another logical flow table for a lookup is a recursive construct, OVN ``programs’’ in practice tend to form deep control stacks that, displayed in the obvious way using additional indentation for each level, quickly use up the horizontal space on all but the widest displays. To make detailed output more readable, without loss of generality, ovn-trace omits indentation for ``tail recursion,’’ that is, when next is the last action in a logical flow, it does not indent details of the next table lookup more deeply. Output still uses indentation when it is needed for clarity.

OVN ``programs’’ traces also tend to encounter long strings of logical flows with match expression 1 (which matches every packet) and the single action next;. These are uninteresting and merely clutter output, so ovn-trace omits them entirely even from detailed output.

The following excerpt from detailed ovn-trace output shows a section for a packet traversing the ingress pipeline of logical datapath ls1 with ingress logical port lp111. The packet matches a logical flow in table 0 (aka ls_in_port_sec_l2) with priority 50 and executes next(1); to pass to table 1. Tables 1 through 11 are trivial and omitted. In table 12 (aka ls_in_l2_lkup), the packet matches a flow with priority 50 based on its Ethernet destination address and the flow’s actions output the packet to the lrp11-attachement logical port.

    ingress(dp="ls1", inport="lp111")


    ---------------------------------


    0. ls_in_port_sec_l2: inport == "lp111", priority 50


    next(1);


    12. ls_in_l2_lkup: eth.dst == 00:00:00:00:ff:11, priority 50


    outport = "lrp11-attachment";


    output;


  

Summary Output

Summary output includes the logical pipelines visited by a packet and the logical actions executed on it. Compared to the detailed output, however, it removes details of tables and logical flows traversed by a packet. It uses a format closer to that of a programming language and does not attempt to avoid indentation. The summary output equivalent to the above detailed output fragment is:

    ingress(dp="ls1", inport="lp111") {


    outport = "lrp11-attachment";


    output;


    ...


    };


  

Minimal Output

Minimal output includes only actions that modify packet data (not including OVN registers or metadata such as outport) and output actions that actually deliver a packet to a logical port (excluding patch ports). The operands of actions that modify packet data are displayed reduced to constants, e.g. ip4.dst = reg0; might be show as ip4.dst = 192.168.0.1; if that was the value actually loaded. This yields output even simpler than the summary format. (Users familiar with Open vSwitch may recognize this as similar in spirit to the datapath actions listed at the bottom of ofproto/trace output.)

The minimal output format reflects the externally seen behavior of the logical networks more than it does the implementation. This makes this output format the most suitable for use in regression tests, because it is least likely to change when logical flow tables are rearranged without semantic change.

Trace Options

--detailed

--summary

--minimal

These options control the form and level of detail in ovn-trace output. If more than one of these options is specified, all of the selected forms are output, in the order listed above, each headed by a banner line. If none of these options is given, --detailed is the default. See Output, above, for a description of each kind of output.

--all

Selects all three forms of output.

--ovs[=remote]

Makes ovn-trace attempt to obtain and display the OpenFlow flows that correspond to each OVN logical flow. To do so, ovn-trace connects to remote (by default, unix:/var/run/openvswitch/br-int.mgmt) over OpenFlow and retrieves the flows. If remote is specified, it must be an active OpenFlow connection method described in ovs-ofctl(8).

To make the best use of the output, it is important to understand the relationship between logical flows and OpenFlow flows. ovn-architecture(7), under Architectural Physical Life Cycle of a Packet, describes this relationship. Keep in mind the following points:

--ct=flags

This option sets the ct_state flags that a ct_next logical action will report. The flags must be a comma- or space-separated list of the following connection tracking flags:

The ct_next action is used to implement the OVN distributed firewall. For testing, useful flag combinations include:

A packet might pass through the connection tracker twice in one trip through OVN: once following egress from a VM as it passes outward through a firewall, and once preceding ingress to a second VM as it passes inward through a firewall. Use multiple --ct options to specify the flags for multiple ct_next actions.

When --ct is unspecified, or when there are fewer --ct options than ct_next actions, the flags default to trk,est.

--friendly-names

--no-friendly-names

When cloud management systems such as OpenStack are layered on top of OVN, they often use long, human-unfriendly names for ports and datapaths, for example, ones that include entire UUIDs. They do usually include friendlier names, but the long, hard-to-read names are the ones that appear in matches and actions. By default, or with --friendly-names, ovn-trace substitutes these friendlier names for the long names in its output. Use --no-friendly-names to disable this behavior; this option might be useful, for example, if a program is going to parse ovn-trace output.

Daemon Options

--pidfile[=pidfile]

Causes a file (by default, program.pid) to be created indicating the PID of the running process. If the pidfile argument is not specified, or if it does not begin with /, then it is created in /var/run/openvswitch.

If --pidfile is not specified, no pidfile is created.

--overwrite-pidfile

By default, when --pidfile is specified and the specified pidfile already exists and is locked by a running process, the daemon refuses to start. Specify --overwrite-pidfile to cause it to instead overwrite the pidfile.

When --pidfile is not specified, this option has no effect.

--detach

Runs this program as a background process. The process forks, and in the child it starts a new session, closes the standard file descriptors (which has the side effect of disabling logging to the console), and changes its current directory to the root (unless --no-chdir is specified). After the child completes its initialization, the parent exits.

--monitor

Creates an additional process to monitor this program. If it dies due to a signal that indicates a programming error (SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV, SIGXCPU, or SIGXFSZ) then the monitor process starts a new copy of it. If the daemon dies or exits for another reason, the monitor process exits.

This option is normally used with --detach, but it also functions without it.

--no-chdir

By default, when --detach is specified, the daemon changes its current working directory to the root directory after it detaches. Otherwise, invoking the daemon from a carelessly chosen directory would prevent the administrator from unmounting the file system that holds that directory.

Specifying --no-chdir suppresses this behavior, preventing the daemon from changing its current working directory. This may be useful for collecting core files, since it is common behavior to write core dumps into the current working directory and the root directory is not a good directory to use.

This option has no effect when --detach is not specified.

--no-self-confinement

By default this daemon will try to self-confine itself to work with files under well-known directories whitelisted at build time. It is better to stick with this default behavior and not to use this flag unless some other Access Control is used to confine daemon. Note that in contrast to other access control implementations that are typically enforced from kernel-space (e.g. DAC or MAC), self-confinement is imposed from the user-space daemon itself and hence should not be considered as a full confinement strategy, but instead should be viewed as an additional layer of security.

--user=user:group

Causes this program to run as a different user specified in user:group, thus dropping most of the root privileges. Short forms user and :group are also allowed, with current user or group assumed, respectively. Only daemons started by the root user accepts this argument.

On Linux, daemons will be granted CAP_IPC_LOCK and CAP_NET_BIND_SERVICES before dropping root privileges. Daemons that interact with a datapath, such as ovs-vswitchd, will be granted three additional capabilities, namely CAP_NET_ADMIN, CAP_NET_BROADCAST and CAP_NET_RAW. The capability change will apply even if the new user is root.

On Windows, this option is not currently supported. For security reasons, specifying this option will cause the daemon process not to start.

Logging Options

-v[spec]

--verbose=[spec]

Sets logging levels. Without any spec, sets the log level for every module and destination to dbg. Otherwise, spec is a list of words separated by spaces or commas or colons, up to one from each category below:

Case is not significant within spec.

Regardless of the log levels set for file, logging to a file will not take place unless --log-file is also specified (see below).

For compatibility with older versions of OVS, any is accepted as a word but has no effect.

-v

--verbose

Sets the maximum logging verbosity level, equivalent to --verbose=dbg.

-vPATTERN:destination:pattern

--verbose=PATTERN:destination:pattern

Sets the log pattern for destination to pattern. Refer to ovs-appctl(8) for a description of the valid syntax for pattern.

-vFACILITY:facility

--verbose=FACILITY:facility

Sets the RFC5424 facility of the log message. facility can be one of kern, user, mail, daemon, auth, syslog, lpr, news, uucp, clock, ftp, ntp, audit, alert, clock2, local0, local1, local2, local3, local4, local5, local6 or local7. If this option is not specified, daemon is used as the default for the local system syslog and local0 is used while sending a message to the target provided via the --syslog-target option.

--log-file[=file]

Enables logging to a file. If file is specified, then it is used as the exact name for the log file. The default log file name used if file is omitted is /var/log/openvswitch/program.log.

--syslog-target=host:port

Send syslog messages to UDP port on host, in addition to the system syslog. The host must be a numerical IP address, not a hostname.

--syslog-method=method

Specify method as how syslog messages should be sent to syslog daemon. The following forms are supported:

PKI Options

PKI configuration is required to use SSL for the connection to the database (and the switch, if --ovs is specified).

Other Options

--db database

The OVSDB database remote to contact. If the OVN_SB_DB environment variable is set, its value is used as the default. Otherwise, the default is unix:/var/run/openvswitch/db.sock, but this default is unlikely to be useful outside of single-machine OVN test environments.