Parsers

linuxnet.qos uses a number of parser classes to parse the output of the tc(8) command:

• QDiscParser

• QClassParser

• TrafficFilterParser

The following classes are also used in parsing:

• QDiscOutput

• QClassOutput

• FilterOutput

• FilterOutputLine

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Queuing discipline parsing

The QDiscParser class is responsible for parsing the output of tc -s qdisc ls dev <interface>.

The QDiscParser.register_qdisc() method must be invoked to register queueing discipline classes.

class QDiscParser(allow_parsing_errors: bool)

Helper class that creates QDisc objects from the output of the tc(8) command.

classmethod register_qdisc(ident: str, klass) → None

Register the given class (which should be a subclass of the QDisc class).

This method is intended to be used for adding support for new queuing disciplines.

Parameters:

• ident – the qdisc name that appears in the tc -s qdisc ls output.

• klass – the Python class for this queuing discipline

class QDiscOutput(line_group: List[str])

Helper class used for parsing tc qdisc ls output for a single qdisc

Parameters:

line_group – list of lines, guaranteed not to be empty

get_handle() → Handle

Returns the (parsed) Handle of the queuing discipline.

get_parent_handle() → Optional[Handle]

Returns the (parsed) Handle of the parent of this queueing discipline, or None if this is a root qdisc

get_refcnt() → Optional[int]

Returns reference count of qdisc (None for non-root qdiscs, and for some root qdiscs like mq)

get_qdisc_line() → str

Returns the tc(8) output qdisc line

get_field_iter() → Iterator[str]

Return an iterator for the (remaining) fields of the qdisc line

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Queuing class parsing

The QClassParser class is responsible for parsing the output of tc -s class ls dev <interface>.

The QClassParser.register_qclass() method must be invoked to register Python classes providing support for classes of classful queueing disciplines.

class QClassParser(allow_parsing_errors: bool)

Helper class that creates QClass objects from the output of the tc(8) command.

classmethod register_qclass(ident: str, klass) → None

Register the given class (which should be a subclass of the QClass class).

This method is intended to be used for adding support for new queuing discipline classes.

Parameters:

• ident – the queuing class name that appears in the tc -s class ls output.

• klass – the Python class for this queuing class

class QClassOutput(line_group: List[str])

Helper class used for parsing tc class ls output for a single qclass

Parameters:

line_group – list of lines, guaranteed not to be empty

get_handle() → Handle

Returns the (parsed) Handle of the queuing class.

get_parent_handle() → Handle

Returns the (parsed) Handle of the parent of the queuing class.

get_qdisc_handle() → Optional[Handle]

Returns the Handle of a (leaf) qdisc

get_class_line() → str

Returns the tc(8) output class line

get_field_iter() → Iterator[str]

Return an iterator for the (remaining) fields of the class line

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Traffic filter parsing

The TrafficFilterParser class is responsible for parsing the output of tc filter ls dev <interface>.

The TrafficFilterParser.register_filter() method must be invoked to register classes traffic filter classes.

class TrafficFilterParser(allow_parsing_errors: bool)

Helper class that creates TrafficFilter objects from the output of the tc(8) command.

classmethod register_filter(*, filter_type: str, protocol: str, klass) → None

Register the given class (which should be a subclass of the TrafficFilter class).

This method is intended to be used for adding support for new traffic filter types.

Parameters:

• filter_type – a tc(8) filter type, e.g. u32

• protocol – a tc(8) protocol name, e.g. ip

• klass – the Python class for this (filter_type, protocol)

classmethod register_action(*, action_name: str, klass) → None

Register the given class (which should be a subclass of the TrafficAction class).

This method is intended to be used for adding support for new traffic actions.

Parameters:

• action_name – tc(8) action, e.g. police

• klass – the Python class for this action

classmethod parse_action(fields: List[str], nfl_iter: Iterator[str]) → TrafficAction

Parse the tc(8) output for a traffic action.

Parameters:

• fields – fields of the output line identifying the action and its arguments; fields[0] is the action type

• nfl_iter – iterator returning the lines after the lines that start with ‘filter’

Return type:

a TrafficAction instance

Raises a TcParsingError if unable to parse the action

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class FilterOutput(proto: str, prio: int, filter_type: str, owner: QNode)

An instance of this class contains the tc(8) output for a single filter.

Parameters:

• proto – filter protocol

• prio – filter priority

• filter_type – filter type

• owner – QDisc/QClass that owns the filter

get_prio() → int

Returns the priority value

get_proto() → str

Returns the protocol value

get_filter_type() → str

Returns the filter type

get_filter_owner() → QNode

Returns the QDisc/QClass that owns the filter

get_first_line() → str

Returns the first line from the tc(8) output for this filter

has_nonfilter_lines() → bool

Returns True if the filter output has any lines not starting with the word filter

filter_lines_iter() → Iterator[FilterOutputLine]

Returns an iterator that returns FilterOutputLine instances.

nonfilter_lines_iter() → Iterator[str]

Returns an iterator that returns lines (strings)

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class FilterOutputLine(line: str, fields: List[str])

A class that holds a line of filter output.

One can iterate over the fields of the line:

def parse_fields(fline: FilterOutputLine):
    for field in fline:
        if field == 'xxx':
            ...

The entire line can be returned by using the str() builtin function.

Parameters:

• line – the complete tc(8) filter line

• fields – list of fields of the line after the filter type