//// vim.syntax: asciidoc Copyright (c) 2011 Thomas Graf //// Routing Family Netlink Library (libnl-route) ============================================ Thomas Graf 3.1, Aug 11 2011: == Introduction This library provides APIs to the kernel interfaces of the routing family. NOTE: Work in progress. == Addresses [[route_link]] == Links (Network Devices) The link configuration interface is part of the +NETLINK_ROUTE+ protocol family and implements the following netlink message types: - View and modify the configuration of physical and virtual network devices. - Create and delete virtual network devices (e.g. dummy devices, VLAN devices, tun devices, bridging devices, ...) - View and modify per link network configuration settings (e.g. +net.ipv6.conf.eth0.accept_ra+, +net.ipv4.conf.eth1.forwarding+, ...) .Naming Convention (network device, link, interface) In networking several terms are commonly used to refer to network devices. While they have distinct meanings they have been used interchangeably in the past. Within the Linux kernel, the term _network device_ or _netdev_ is commonly used In user space the term _network interface_ is very common. The routing netlink protocol uses the term _link_ and so does the _iproute2_ utility and most routing daemons. === Netlink Protocol This section describes the protocol semantics of the netlink based link configuration interface. The following messages are defined: [options="header", cols="1,2,2"] |============================================================================== | Message Type | User -> Kernel | Kernel -> User | +RTM_NEWLINK+ | Create or update virtual network device | Reply to +RTM_GETLINK+ request or notification of link added or updated | +RTM_DELLINK+ | Delete virtual network device | Notification of link deleted or disappeared | +RTM_GETLINK+ | Retrieve link configuration and statistics | | +RTM_SETLINK+ | Modify link configuration | |============================================================================== See link:core.html#core_msg_types[Netlink Library - Message Types] for more information on common semantics of these message types. ==== Link Message Format All netlink link messages share a common header (+struct ifinfomsg+) which is appended after the netlink header (+struct nlmsghdr+). image:ifinfomsg.png["Link Message Header"] The meaning of each field may differ depending on the message type. A +struct ifinfomsg+ is defined in ++ to represent the header. Address Family (8bit):: The address family is usually set to +AF_UNSPEC+ but may be specified in +RTM_GETLINK+ requests to limit the returned links to a specific address family. Link Layer Type (16bit):: Currently only used in kernel->user messages to report the link layer type of a link. The value corresponds to the +ARPHRD_*+ defines found in ++. Translation from/to strings can be done using the functions nl_llproto2str()/nl_str2llproto(). Link Index (32bit):: Carries the interface index and is used to identify existing links. Flags (32bit):: In kernel->user messages the value of this field represents the current state of the link flags. In user->kernel messages this field is used to change flags or set the initial flag state of new links. Note that in order to change a flag, the flag must also be set in the _Flags Change Mask_ field. Flags Change Mask (32bit):: The primary use of this field is to specify a mask of flags that should be changed based on the value of the _Flags_ field. A special meaning is given to this field when present in link notifications, see TODO. Attributes (variable):: All link message types may carry netlink attributes. They are defined in the header file and share the prefix +IFLA_+. ==== Link Message Types .RTM_GETLINK (user->kernel) Lookup link by 1. interface index or 2. link name (+IFLA_IFNAME+) and return a single +RTM_NEWLINK+ message containing the link configuration and statistics or a netlink error message if no such link was found. *Parameters:* * *Address family* ** If the address family is set to +PF_BRIDGE+, only bridging devices will be returned. ** If the address family is set to +PF_INET6+, only ipv6 enabled devices will be returned. *Flags:* * +NLM_F_DUMP+ If set, all links will be returned in form of a multipart message. *Returns:* * +EINVAL+ if neither interface nor link name are set * +ENODEV+ if no link was found * +ENOBUFS+ if allocation failed .RTM_NEWLINK (user->kernel) Creates a new or updates an existing link. Only virtual links may be created but all links may be updated. *Flags:* - +NLM_F_CREATE+ Create link if it does not exist - +NLM_F_EXCL+ Return +EEXIST+ if link already exists *Returns:* - +EINVAL+ malformed message or invalid configuration parameters - +EAFNOSUPPORT+ if a address family specific configuration (+IFLA_AF_SPEC+) is not supported. - +EOPNOTSUPP+ if the link does not support modification of parameters - +EEXIST+ if +NLM_F_EXCL+ was set and the link exists alraedy - +ENODEV+ if the link does not exist and +NLM_F_CREATE+ is not set .RTM_NEWLINK (kernel->user) This message type is used in reply to a +RTM_GETLINK+ request and carries the configuration and statistics of a link. If multiple links need to be sent, the messages will be sent in form of a multipart message. The message type is also used for notifications sent by the kernel to the multicast group +RTNLGRP_LINK+ to inform about various link events. It is therefore recommended to always use a separate link socket for link notifications in order to separate between the two message types. TODO: document how to detect different notifications .RTM_DELLINK (user->kernel) Lookup link by 1. interface index or 2. link name (+IFLA_IFNAME+) and delete the virtual link. *Returns:* * +EINVAL+ if neither interface nor link name are set * +ENODEV+ if no link was found * +ENOTSUPP+ if the operation is not supported (not a virtual link) .RTM_DELLINK (kernel->user) Notification sent by the kernel to the multicast group +RTNLGRP_LINK+ when a. a network device was unregistered (change == ~0) b. a bridging device was deleted (address family will be +PF_BRIDGE+) === Get / List [[link_list]] ==== Get list of links To retrieve the list of links in the kernel, allocate a new link cache using +rtnl_link_alloc_cache()+ to hold the links. It will automatically construct and send a +RTM_GETLINK+ message requesting a dump of all links from the kernel and feed the returned +RTM_NEWLINK+ to the internal link message parser which adds the returned links to the cache. [source,c] ----- #include int rtnl_link_alloc_cache(struct nl_sock *sk, int family, struct nl_cache **result) ----- The cache will contain link objects (+struct rtnl_link+, see <>) and can be accessed using the standard cache functions. By setting the +family+ parameter to an address familly other than +AF_UNSPEC+, the resulting cache will only contain links supporting the specified address family. The following direct search functions are provided to search by interface index and by link name: [source,c] ----- #include struct rtnl_link *rtnl_link_get(struct nl_cache *cache, int ifindex); struct rtnl_link *rtnl_link_get_by_name(struct nl_cache *cache, const char *name); ----- .Example: Link Cache [source,c] ----- struct nl_cache *cache; struct rtnl_link *link; if (rtnl_link_alloc_cache(sock, AF_UNSPEC, &cache)) < 0) /* error */ if (!(link = rtnl_link_get_by_name(cache, "eth1"))) /* link does not exist */ /* do something with link */ rtnl_link_put(link); nl_cache_put(cache); ----- [[link_direct_lookup]] ==== Lookup Single Link (Direct Lookup) If only a single link is of interest, the link can be looked up directly without the use of a link cache using the function +rtnl_link_get_kernel()+. [source,c] ----- #include int rtnl_link_get_kernel(struct nl_sock *sk, int ifindex, const char *name, struct rtnl_link **result); ----- It will construct and send a +RTM_GETLINK+ request using the parameters provided and wait for a +RTM_NEWLINK+ or netlink error message sent in return. If the link exists, the link is returned as link object (see <>). .Example: Direct link lookup [source,c] ----- struct rtnl_link *link; if (rtnl_link_get_kernel(sock, 0, "eth1", &link) < 0) /* error */ /* do something with link */ rtnl_link_put(link); ----- NOTE: While using this function can save a substantial amount of bandwidth on the netlink socket, the result will not be cached, subsequent calls to rtnl_link_get_kernel() will always trigger sending a +RTM_GETLINK+ request. [[link_translate_ifindex]] ==== Translating interface index to link name Applications which require to translate interface index to a link name or vice verase may use the following functions to do so. Both functions require a filled link cache to work with. [source,c] ----- char *rtnl_link_i2name (struct nl_cache *cache, int ifindex, char *dst, size_t len); int rtnl_link_name2i (struct nl_cache *cache, const char *name); ----- === Add / Modify Several types of virtual link can be added on the fly using the function +rtnl_link_add()+. [source,c] ----- #include int rtnl_link_add(struct nl_sock *sk, struct rtnl_link *link, int flags); ----- === Delete The deletion of virtual links such as VLAN devices or dummy devices is done using the function +rtnl_link_delete()+. The link passed on to the function can be a link from a link cache or it can be construct with the minimal attributes needed to identify the link. [source,c] ----- #include int rtnl_link_delete(struct nl_sock *sk, const struct rtnl_link *link); ----- The function will construct and send a +RTM_DELLINK+ request message and returns any errors returned by the kernel. .Example: Delete link by name [source,c] ----- struct rtnl_link *link; if (!(link = rtnl_link_alloc())) /* error */ rtnl_link_set_name(link, "my_vlan"); if (rtnl_link_delete(sock, link) < 0) /* error */ rtnl_link_put(link); ----- [[link_object]] === Link Object A link is represented by the structure +struct rtnl_link+. Instances may be created with the function +rtnl_link_alloc()+ or via a link cache (see <>) and are freed again using the function +rtnl_link_put()+. [source,c] ----- #include struct rtnl_link *rtnl_link_alloc(void); void rtnl_link_put(struct rtnl_link *link); ----- [[link_attr_name]] ==== Name The name serves as unique, human readable description of the link. By default, links are named based on their type and then enumerated, e.g. eth0, eth1, ethn but they may be renamed at any time. Kernels >= 2.6.11 support identification by link name. [source,c] ----- #include void rtnl_link_set_name(struct rtnl_link *link, const char *name); char *rtnl_link_get_name(struct rtnl_link *link); ----- *Accepted link name format:* +[^ /]*+ (maximum length: 15 characters) [[link_attr_ifindex]] ==== Interface Index (Identifier) The interface index is an integer uniquely identifying a link. If present in any link message, it will be used to identify an existing link. [source,c] ----- #include void rtnl_link_set_ifindex(struct rtnl_link *link, int ifindex); int rtnl_link_get_ifindex(struct rtnl_link *link); ----- [[link_attr_group]] ==== Group Each link can be assigned a numeric group identifier to group a bunch of links together and apply a set of changes to a group instead of just a single link. [source,c] ----- #include void rtnl_link_set_group(struct rtnl_link *link, uint32_t group); uint32_t rtnl_link_get_group(struct rtnl_link *link); ----- [[link_attr_address]] ==== Link Layer Address The link layer address (e.g. MAC address). [source,c] ----- #include void rtnl_link_set_addr(struct rtnl_link *link, struct nl_addr *addr); struct nl_addr *rtnl_link_get_addr(struct rtnl_link *link); ----- [[link_attr_broadcast]] ==== Broadcast Address The link layer broadcast address [source,c] ----- #include void rtnl_link_set_broadcast(struct rtnl_link *link, struct nl_addr *addr); struct nl_addr *rtnl_link_get_broadcast(struct rtnl_link *link); ----- [[link_attr_mtu]] ==== MTU (Maximum Transmission Unit) The maximum transmission unit specifies the maximum packet size a network device can transmit or receive. This value may be lower than the capability of the physical network device. [source,c] ----- #include void rtnl_link_set_mtu(struct rtnl_link *link, unsigned int mtu); unsigned int rtnl_link_get_mtu(struct rtnl_link *link); ----- [[link_attr_flags]] ==== Flags The flags of a link enable or disable various link features or inform about the state of the link. [source,c] ----- #include void rtnl_link_set_flags(struct rtnl_link *link, unsigned int flags); void rtnl_link_unset_flags(struct rtnl_link *link, unsigned int flags); unsigned int rtnl_link_get_flags(struct rtnl_link *link); ----- [options="compact"] [horizontal] IFF_UP:: Link is up (administratively) IFF_RUNNING:: Link is up and carrier is OK (RFC2863 OPER_UP) IFF_LOWER_UP:: Link layer is operational IFF_DORMANT:: Driver signals dormant IFF_BROADCAST:: Link supports broadcasting IFF_MULTICAST:: Link supports multicasting IFF_ALLMULTI:: Link supports multicast routing IFF_DEBUG:: Tell driver to do debugging (currently unused) IFF_LOOPBACK:: Link loopback network IFF_POINTOPOINT:: Point-to-point link IFF_NOARP:: ARP is not supported IFF_PROMISC:: Status of promiscious mode IFF_MASTER:: Master of a load balancer (bonding) IFF_SLAVE:: Slave to a master link IFF_PORTSEL:: Driver supports setting media type (only used by ARM ethernet) IFF_AUTOMEDIA:: Link selects port automatically (only used by ARM ethernet) IFF_ECHO:: Echo sent packets (testing feature, CAN only) IFF_DYNAMIC:: Unused (BSD compatibility) IFF_NOTRAILERS:: Unused (BSD compatibility) To translate a link flag to a link flag name or vice versa: [source,c] ----- #include char *rtnl_link_flags2str(int flags, char *buf, size_t size); int rtnl_link_str2flags(const char *flag_name); ----- [[link_attr_txqlen]] ==== Transmission Queue Length The transmission queue holds packets before packets are delivered to the driver for transmission. It is usually specified in number of packets but the unit may be specific to the link type. [source,c] ----- #include void rtnl_link_set_txqlen(struct rtnl_link *link, unsigned int txqlen); unsigned int rtnl_link_get_txqlen(struct rtnl_link *link); ----- [[link_attr_operstate]] ==== Operational Status The operational status has been introduced to provide extended information on the link status. Traditionally the link state has been described using the link flags +IFF_UP, IFF_RUNNING, IFF_LOWER_UP+, and +IFF_DORMANT+ which was no longer sufficient for some link types. [source,c] ----- #include void rtnl_link_set_operstate(struct rtnl_link *link, uint8_t state); uint8_t rtnl_link_get_operstate(struct rtnl_link *link); ----- [options="compact"] [horizontal] IF_OPER_UNKNOWN:: Unknown state IF_OPER_NOTPRESENT:: Link not present IF_OPER_DOWN:: Link down IF_OPER_LOWERLAYERDOWN:: L1 down IF_OPER_TESTING:: Testing IF_OPER_DORMANT:: Dormant IF_OPER_UP:: Link up Translation of operational status code to string and vice versa: [source,c] ----- #include char *rtnl_link_operstate2str(uint8_t state, char *buf, size_t size); int rtnl_link_str2operstate(const char *name); ----- [[link_attr_mode]] ==== Mode Currently known link modes are: [options="compact"] [horizontal] IF_LINK_MODE_DEFAULT:: Default link mode IF_LINK_MODE_DORMANT:: Limit upward transition to dormant [source,c] ----- #include void rtnl_link_set_linkmode(struct rtnl_link *link, uint8_t mode); uint8_t rtnl_link_get_linkmode(struct rtnl_link *link); ----- Translation of link mode to string and vice versa: [source,c] ----- char *rtnl_link_mode2str(uint8_t mode, char *buf, size_t len); uint8_t rtnl_link_str2mode(const char *name); ----- [[link_attr_alias]] ==== IfAlias Alternative name for the link, primarly used for SNMP IfAlias. [source,c] ----- #include const char *rtnl_link_get_ifalias(struct rtnl_link *link); void rtnl_link_set_ifalias(struct rtnl_link *link, const char *alias); ----- *Length limit:* 256 [[link_attr_arptype]] ==== Hardware Type [source,c] ----- #include #include void rtnl_link_set_arptype(struct rtnl_link *link, unsigned int arptype); unsigned int rtnl_link_get_arptype(struct rtnl_link *link); ---- Translation of hardware type to character string and vice versa: [source,c] ----- #include char *nl_llproto2str(int arptype, char *buf, size_t len); int nl_str2llproto(const char *name); ----- [[link_attr_qdisc]] ==== Qdisc The name of the queueing discipline used by the link is of informational nature only. It is a read-only attribute provided by the kernel and cannot be modified. The set function is provided solely for the purpose of creating link objects to be used for comparison. For more information on how to modify the qdisc of a link, see section <>. [source,c] ----- #include void rtnl_link_set_qdisc(struct rtnl_link *link, const char *name); char *rtnl_link_get_qdisc(struct rtnl_link *link); ----- [[link_attr_promiscuity]] ==== Promiscuity The number of subsystem currently depending on the link being promiscuous mode. A value of 0 indicates that the link is not in promiscuous mode. It is a read-only attribute provided by the kernel and cannot be modified. The set function is provided solely for the purpose of creating link objects to be used for comparison. [source,c] ----- #include void rtnl_link_set_promiscuity(struct rtnl_link *link, uint32_t count); uint32_t rtnl_link_get_promiscuity(struct rtnl_link *link); ----- [[link_num_rxtx_queues]] ==== RX/TX Queues The number of RX/TX queues the link provides. The attribute is writable but will only be considered when creating a new network device via netlink. [source,c] ----- #include void rtnl_link_set_num_tx_queues(struct rtnl_link *link, uint32_t nqueues); uint32_t rtnl_link_get_num_tx_queues(struct rtnl_link *link); void rtnl_link_set_num_rx_queues(struct rtnl_link *link, uint32_t nqueues); uint32_t rtnl_link_get_num_rx_queues(struct rtnl_link *link); ----- [[link_attr_weight]] ==== Weight This attribute is unused and obsoleted in all recent kernels. [[link_modules]] === Modules [[link_bonding]] ==== Bonding .Example: Add bonding link [source,c] ----- #include struct rtnl_link *link; link = rtnl_link_bond_alloc(); rtnl_link_set_name(link, "my_bond"); /* requires admin privileges */ if (rtnl_link_add(sk, link, NLM_F_CREATE) < 0) /* error */ rtnl_link_put(link); ----- [[link_vlan]] ==== VLAN [source,c] ----- extern char * rtnl_link_vlan_flags2str(int, char *, size_t); extern int rtnl_link_vlan_str2flags(const char *); extern int rtnl_link_vlan_set_id(struct rtnl_link *, int); extern int rtnl_link_vlan_get_id(struct rtnl_link *); extern int rtnl_link_vlan_set_flags(struct rtnl_link *, unsigned int); extern int rtnl_link_vlan_unset_flags(struct rtnl_link *, unsigned int); extern unsigned int rtnl_link_vlan_get_flags(struct rtnl_link *); extern int rtnl_link_vlan_set_ingress_map(struct rtnl_link *, int, uint32_t); extern uint32_t * rtnl_link_vlan_get_ingress_map(struct rtnl_link *); extern int rtnl_link_vlan_set_egress_map(struct rtnl_link *, uint32_t, int); extern struct vlan_map *rtnl_link_vlan_get_egress_map(struct rtnl_link *, int *); ----- .Example: Add a VLAN device [source,c] ----- struct rtnl_link *link; int master_index; /* lookup interface index of eth0 */ if (!(master_index = rtnl_link_name2i(link_cache, "eth0"))) /* error */ /* allocate new link object of type vlan */ link = rtnl_link_vlan_alloc(); /* set eth0 to be our master device */ rtnl_link_set_link(link, master_index); rtnl_link_vlan_set_id(link, 10); if ((err = rtnl_link_add(sk, link, NLM_F_CREATE)) < 0) /* error */ rtnl_link_put(link); ----- [[link_macvlan]] ==== MACVLAN [source,c] ----- extern struct rtnl_link *rtnl_link_macvlan_alloc(void); extern int rtnl_link_is_macvlan(struct rtnl_link *); extern char * rtnl_link_macvlan_mode2str(int, char *, size_t); extern int rtnl_link_macvlan_str2mode(const char *); extern char * rtnl_link_macvlan_flags2str(int, char *, size_t); extern int rtnl_link_macvlan_str2flags(const char *); extern int rtnl_link_macvlan_set_mode(struct rtnl_link *, uint32_t); extern uint32_t rtnl_link_macvlan_get_mode(struct rtnl_link *); extern int rtnl_link_macvlan_set_flags(struct rtnl_link *, uint16_t); extern int rtnl_link_macvlan_unset_flags(struct rtnl_link *, uint16_t); extern uint16_t rtnl_link_macvlan_get_flags(struct rtnl_link *); ----- .Example: Add a MACVLAN device [source,c] ----- struct rtnl_link *link; int master_index; struct nl_addr* addr; /* lookup interface index of eth0 */ if (!(master_index = rtnl_link_name2i(link_cache, "eth0"))) /* error */ /* allocate new link object of type macvlan */ link = rtnl_link_macvlan_alloc(); /* set eth0 to be our master device */ rtnl_link_set_link(link, master_index); /* set address of virtual interface */ addr = nl_addr_build(AF_LLC, ether_aton("00:11:22:33:44:55"), ETH_ALEN); rtnl_link_set_addr(link, addr); nl_addr_put(addr); /* set mode of virtual interface */ rtnl_link_macvlan_set_mode(link, rtnl_link_macvlan_str2mode("bridge")); if ((err = rtnl_link_add(sk, link, NLM_F_CREATE)) < 0) /* error */ rtnl_link_put(link); ----- == Neighbouring == Routing [[route_tc]] == Traffic Control The traffic control architecture allows the queueing and prioritization of packets before they are enqueued to the network driver. To a limited degree it is also possible to take control of network traffic as it enters the network stack. The architecture consists of three different types of modules: - *Queueing disciplines (qdisc)* provide a mechanism to enqueue packets in different forms. They may be used to implement fair queueing, prioritization of differentiated services, enforce bandwidth limitations, or even to simulate network behaviour such as packet loss and packet delay. Qdiscs can be classful in which case they allow traffic classes described in the next paragraph to be attached to them. - *Traffic classes (class)* are supported by several qdiscs to build a tree structure for different types of traffic. Each class may be assigned its own set of attributes such as bandwidth limits or queueing priorities. Some qdiscs even allow borrowing of bandwidth between classes. - *Classifiers (cls)* are used to decide which qdisc/class the packet should be enqueued to. Different types of classifiers exists, ranging from classification based on protocol header values to classification based on packet priority or firewall marks. Additionally most classifiers support *extended matches (ematch)* which allow extending classifiers by a set of matcher modules, and *actions* which allow classifiers to take actions such as mangling, mirroring, or even rerouting of packets. .Default Qdisc The default qdisc used on all network devices is `pfifo_fast`. Network devices which do not require a transmit queue such as the loopback device do not have a default qdisc attached. The `pfifo_fast` qdisc provides three bands to prioritize interactive traffic over bulk traffic. Classification is based on the packet priority (diffserv). image:qdisc_default.png["Default Qdisc"] .Multiqueue Default Qdisc If the network device provides multiple transmit queues the `mq` qdisc is used by default. It will automatically create a separate class for each transmit queue available and will also replace the single per device tx lock with a per queue lock. image:qdisc_mq.png["Multiqueue default Qdisc"] .Example of a customized classful qdisc setup The following figure illustrates a possible combination of different queueing and classification modules to implement quality of service needs. image:tc_overview.png["Classful Qdisc diagram"] === Traffic Control Object Each type traffic control module (qdisc, class, classifier) is represented by its own structure. All of them are based on the traffic control object represented by `struct rtnl_tc` which itself is based on the generic object `struct nl_object` to make it cacheable. The traffic control object contains all attributes, implementation details and statistics that are shared by all of the traffic control object types. image:tc_obj.png["struct rtnl_tc hierarchy"] It is not possible to allocate a `struct rtnl_tc` object, instead the actual tc object types must be allocated directly using `rtnl_qdisc_alloc()`, `rtnl_class_alloc()`, `rtnl_cls_alloc()` and then casted to `struct rtnl_tc` using the `TC_CAST()` macro. .Usage Example: Allocation, Casting, Freeing [source,c] ----- #include #include struct rtnl_qdisc *qdisc; /* Allocation of a qdisc object */ qdisc = rtnl_qdisc_alloc(); /* Cast the qdisc to a tc object using TC_CAST() to use rtnl_tc_ functions. */ rtnl_tc_set_mpu(TC_CAST(qdisc), 64); /* Free the qdisc object */ rtnl_qdisc_put(qdisc); ----- [[tc_attr]] ==== Attributes Handle:: The handle uniquely identifies a tc object and is used to refer to other tc objects when constructing tc trees. + [source,c] ----- void rtnl_tc_set_handle(struct rtnl_tc *tc, uint32_t handle); uint32_t rtnl_tc_get_handle(struct rtnl_tc *tc); ----- Interface Index:: The interface index specifies the network device the traffic object is attached to. The function `rtnl_tc_set_link()` should be preferred when setting the interface index. It stores the reference to the link object in the tc object and allows retrieving the `mtu` and `linktype` automatically. + [source,c] ----- void rtnl_tc_set_ifindex(struct rtnl_tc *tc, int ifindex); void rtnl_tc_set_link(struct rtnl_tc *tc, struct rtnl_link *link); int rtnl_tc_get_ifindex(struct rtnl_tc *tc); ----- Link Type:: The link type specifies the kind of link that is used by the network device (e.g. ethernet, ATM, ...). It is derived automatically when the network device is specified with `rtnl_tc_set_link()`. The default fallback is `ARPHRD_ETHER` (ethernet). + [source,c] ----- void rtnl_tc_set_linktype(struct rtnl_tc *tc, uint32_t type); uint32_t rtnl_tc_get_linktype(struct rtnl_tc *tc); ----- Kind:: The kind character string specifies the type of qdisc, class, classifier. Setting the kind results in the module specific structure being allocated. Therefore it is imperative to call `rtnl_tc_set_kind()` before using any type specific API functions such as `rtnl_htb_set_rate()`. + [source,c] ----- int rtnl_tc_set_kind(struct rtnl_tc *tc, const char *kind); char *rtnl_tc_get_kind(struct rtnl_tc *tc); ----- MPU:: The Minimum Packet Unit specifies the minimum packet size which will be transmitted ever be seen by this traffic control object. This value is used for rate calculations. Not all object implementations will make use of this value. The default value is 0. + [source,c] ----- void rtnl_tc_set_mpu(struct rtnl_tc *tc, uint32_t mpu); uint32_t rtnl_tc_get_mpu(struct rtnl_tc *tc); ----- MTU:: The Maximum Transmission Unit specifies the maximum packet size which will be transmitted. The value is derived from the link specified with `rtnl_tc_set_link()` if not overwritten with `rtnl_tc_set_mtu()`. If no link and MTU is specified, the value defaults to 1500 (ethernet). + [source,c] ----- void rtnl_tc_set_mtu(struct rtnl_tc *tc, uint32_t mtu); uint32_t rtnl_tc_get_mtu(struct rtnl_tc *tc); ----- Overhead:: The overhead specifies the additional overhead per packet caused by the network layer. This value can be used to correct packet size calculations if the packet size on the wire does not match the packet size seen by the kernel. The default value is 0. + [source,c] ----- void rtnl_tc_set_overhead(struct rtnl_tc *tc, uint32_t overhead); uint32_t rtnl_tc_get_overhead(struct rtnl_tc *tc); ----- Parent:: Specifies the parent traffic control object. The parent is identifier by its handle. Special values are: - `TC_H_ROOT`: attach tc object directly to network device (root qdisc, root classifier) - `TC_H_INGRESS`: same as `TC_H_ROOT` but on the ingress side of the network stack. + [source,c] ----- void rtnl_tc_set_parent(struct rtnl_tc *tc, uint32_t parent); uint32_t rtnl_tc_get_parent(struct rtnl_tc *tc); ----- Statistics:: Generic statistics, see <> for additional information. + [source,c] ----- uint64_t rtnl_tc_get_stat(struct rtnl_tc *tc, enum rtnl_tc_stat id); ----- [[tc_stats]] ==== Accessing Statistics The traffic control object holds a set of generic statistics. Not all traffic control modules will make use of all of these statistics. Some modules may provide additional statistics via their own APIs. .Statistic identifiers `(enum rtnl_tc_stat)` [cols="m,,", options="header", frame="topbot"] |==================================================================== | ID | Type | Description | RTNL_TC_PACKETS | Counter | Total # of packets transmitted | RTNL_TC_BYTES | Counter | Total # of bytes transmitted | RTNL_TC_RATE_BPS | Rate | Current bytes/s rate | RTNL_TC_RATE_PPS | Rate | Current packets/s rate | RTNL_TC_QLEN | Rate | Current length of the queue | RTNL_TC_BACKLOG | Rate | # of packets currently backloged | RTNL_TC_DROPS | Counter | # of packets dropped | RTNL_TC_REQUEUES | Counter | # of packets requeued | RTNL_TC_OVERLIMITS | Counter | # of packets that exceeded the limit |==================================================================== NOTE: `RTNL_TC_RATE_BPS` and `RTNL_TC_RATE_PPS` only return meaningful values if a rate estimator has been configured. .Usage Example: Retrieving tc statistics [source,c] ------- #include uint64_t drops, qlen; drops = rtnl_tc_get_stat(TC_CAST(qdisc), RTNL_TC_DROPS); qlen = rtnl_tc_get_stat(TC_CAST(qdisc), RTNL_TC_QLEN); ------- ==== Rate Table Calculations [[tc_qdisc]] === Queueing Discipline (qdisc) .Classless Qdisc The queueing discipline (qdisc) is used to implement fair queueing, priorization or rate control. It provides a _enqueue()_ and _dequeue()_ operation. Whenever a network packet leaves the networking stack over a network device, be it a physical or virtual device, it will be enqueued to a qdisc unless the device is queueless. The _enqueue()_ operation is followed by an immediate call to _dequeue()_ for the same qdisc to eventually retrieve a packet which can be scheduled for transmission by the driver. Additionally, the networking stack runs a watchdog which polls the qdisc regularly to dequeue and send packets even if no new packets are being enqueued. This additional watchdog is required due to the fact that qdiscs may hold on to packets and not return any packets upon _dequeue()_ in order to enforce bandwidth restrictions. image:classless_qdisc_nbands.png[alt="Multiband Qdisc", float="right"] The figure illustrates a trivial example of a classless qdisc consisting of three bands (queues). Use of multiple bands is a common technique in qdiscs to implement fair queueing between flows or prioritize differentiated services. Classless qdiscs can be regarded as a blackbox, their inner workings can only be steered using the configuration parameters provided by the qdisc. There is no way of taking influence on the structure of its internal queues itself. .Classful Qdisc Classful qdiscs allow for the queueing structure and classification process to be created by the user. image:classful_qdisc.png["Classful Qdisc"] The figure above shows a classful qdisc with a classifier attached to it which will make the decision whether to enqueue a packet to traffic class +1:1+ or +1:2+. Unlike with classless qdiscs, classful qdiscs allow the classification process and the structure of the queues to be defined by the user. This allows for complex traffic class rules to be applied. .List of Qdisc Implementations [options="header", frame="topbot", cols="2,1^,8"] |====================================================================== | Qdisc | Classful | Description | ATM | Yes | FIXME | Blackhole | No | This qdisc will drop all packets passed to it. | CBQ | Yes | The CBQ (Class Based Queueing) is a classful qdisc which allows creating traffic classes and enforce bandwidth limitations for each class. | DRR | Yes | The DRR (Deficit Round Robin) scheduler is a classful qdisc impelemting fair queueing. Each class is assigned a quantum specyfing the maximum number of bytes that can be served per round. Unused quantum at the end of the round is carried over to the next round. | DSMARK | Yes | FIXME | FIFO | No | FIXME | GRED | No | FIXME | HFSC | Yes | FIXME | HTB | Yes | FIXME | mq | Yes | FIXME | multiq | Yes | FIXME | netem | No | FIXME | Prio | Yes | FIXME | RED | Yes | FIXME | SFQ | Yes | FIXME | TBF | Yes | FIXME | teql | No | FIXME |====================================================================== .QDisc API Overview [cols="a,a", options="header", frame="topbot"] |==================================================================== | Attribute | C Interface | Allocation / Freeing:: | [source,c] ----- struct rtnl_qdisc *rtnl_qdisc_alloc(void); void rtnl_qdisc_put(struct rtnl_qdisc *qdisc); ----- | Addition:: | [source,c] ----- int rtnl_qdisc_build_add_request(struct rtnl_qdisc *qdisc, int flags, struct nl_msg **result); int rtnl_qdisc_add(struct nl_sock *sock, struct rtnl_qdisc *qdisc, int flags); ----- | Modification:: | [source,c] ----- int rtnl_qdisc_build_change_request(struct rtnl_qdisc *old, struct rtnl_qdisc *new, struct nl_msg **result); int rtnl_qdisc_change(struct nl_sock *sock, struct rtnl_qdisc *old, struct rtnl_qdisc *new); ----- | Deletion:: | [source,c] ----- int rtnl_qdisc_build_delete_request(struct rtnl_qdisc *qdisc, struct nl_msg **result); int rtnl_qdisc_delete(struct nl_sock *sock, struct rtnl_qdisc *qdisc); ----- | Cache:: | [source,c] ----- int rtnl_qdisc_alloc_cache(struct nl_sock *sock, struct nl_cache **cache); struct rtnl_qdisc *rtnl_qdisc_get(struct nl_cache *cache, int, uint32_t); struct rtnl_qdisc *rtnl_qdisc_get_by_parent(struct nl_cache *, int, uint32_t); ----- |==================================================================== [[qdisc_get]] ==== Retrieving Qdisc Configuration The function rtnl_qdisc_alloc_cache() is used to retrieve the current qdisc configuration in the kernel. It will construct a +RTM_GETQDISC+ netlink message, requesting the complete list of qdiscs configured in the kernel. [source,c] ------- #include struct nl_cache *all_qdiscs; if (rtnl_link_alloc_cache(sock, &all_qdiscs) < 0) /* error while retrieving qdisc cfg */ ------- The cache can be accessed using the following functions: - Search qdisc with matching ifindex and handle: + [source,c] -------- struct rtnl_qdisc *rtnl_qdisc_get(struct nl_cache *cache, int ifindex, uint32_t handle); -------- - Search qdisc with matching ifindex and parent: + [source,c] -------- struct rtnl_qdisc *rtnl_qdisc_get_by_parent(struct nl_cache *cache, int ifindex , uint32_t parent); -------- - Or any of the generic cache functions (e.g. nl_cache_search(), nl_cache_dump(), etc.) .Example: Search and print qdisc [source,c] ------- struct rtnl_qdisc *qdisc; int ifindex; ifindex = rtnl_link_get_ifindex(eth0_obj); /* search for qdisc on eth0 with handle 1:0 */ if (!(qdisc = rtnl_qdisc_get(all_qdiscs, ifindex, TC_HANDLE(1, 0)))) /* no such qdisc found */ nl_object_dump(OBJ_CAST(qdisc), NULL); rtnl_qdisc_put(qdisc); ------- [[qdisc_add]] ==== Adding a Qdisc In order to add a new qdisc to the kernel, a qdisc object needs to be allocated. It will hold all attributes of the new qdisc. [source,c] ----- #include struct rtnl_qdisc *qdisc; if (!(qdisc = rtnl_qdisc_alloc())) /* OOM error */ ----- The next step is to specify all generic qdisc attributes using the tc object interface described in the section <>. The following attributes must be specified: - IfIndex - Parent - Kind [source,c] ----- /* Attach qdisc to device eth0 */ rtnl_tc_set_link(TC_CAST(qdisc), eth0_obj); /* Make this the root qdisc */ rtnl_tc_set_parent(TC_CAST(qdisc), TC_H_ROOT); /* Set qdisc identifier to 1:0, if left unspecified, a handle will be generated by the kernel. */ rtnl_tc_set_handle(TC_CAST(qdisc), TC_HANDLE(1, 0)); /* Make this a HTB qdisc */ rtnl_tc_set_kind(TC_CAST(qdisc), "htb"); ----- After specyfing the qdisc kind (rtnl_tc_set_kind()) the qdisc type specific interface can be used to set attributes which are specific to the respective qdisc implementations: [source,c] ------ /* HTB feature: Make unclassified packets go to traffic class 1:5 */ rtnl_htb_set_defcls(qdisc, TC_HANDLE(1, 5)); ------ Finally, the qdisc is ready to be added and can be passed on to the function rntl_qdisc_add() which takes care of constructing a netlink message requesting the addition of the new qdisc, sends the message to the kernel and waits for the response by the kernel. The function returns 0 if the qdisc has been added or updated successfully or a negative error code if an error occured. CAUTION: The kernel operation for updating and adding a qdisc is the same. Therefore when calling rtnl_qdisc_add() any existing qdisc with matching handle will be updated unless the flag NLM_F_EXCL is specified. The following flags may be specified: [horizontal] NLM_F_CREATE:: Create qdisc if it does not exist, otherwise -NLE_OBJ_NOTFOUND is returned. NLM_F_REPLACE:: If another qdisc is already attached to the same parent and their handles mismatch, replace the qdisc instead of returning -EEXIST. NLM_F_EXCL:: Return -NLE_EXISTS if a qdisc with matching handles exists already. WARNING: The function rtnl_qdisc_add() requires administrator privileges. [source,c] ------ /* Submit request to kernel and wait for response */ err = rtnl_qdisc_add(sock, qdisc, NLM_F_CREATE); /* Return the qdisc object to free memory resources */ rtnl_qdisc_put(qdisc); if (err < 0) { fprintf(stderr, "Unable to add qdisc: %s\n", nl_geterror(err)); return err; } ------ ==== Deleting a qdisc [source,c] ------ #include struct rtnl_qdisc *qdisc; qdisc = rtnl_qdisc_alloc(); rtnl_tc_set_link(TC_CAST(qdisc), eth0_obj); rtnl_tc_set_parent(TC_CAST(qdisc), TC_H_ROOT); rtnl_qdisc_delete(sock, qdisc) rtnl_qdisc_put(qdisc); ------ WARNING: The function rtnl_qdisc_delete() requires administrator privileges. [[qdisc_htb]] ==== HTB - Hierarchical Token Bucket .HTB Qdisc Attributes Default Class:: The default class is the fallback class to which all traffic which remained unclassified is directed to. If no default class or an invalid default class is specified, packets are transmitted directly to the next layer (direct transmissions). + [source,c] ----- uint32_t rtnl_htb_get_defcls(struct rtnl_qdisc *qdisc); int rtnl_htb_set_defcls(struct rtnl_qdisc *qdisc, uint32_t defcls); ----- Rate to Quantum (r2q):: TODO + [source,c] ----- uint32_t rtnl_htb_get_rate2quantum(struct rtnl_qdisc *qdisc); int rtnl_htb_set_rate2quantum(struct rtnl_qdisc *qdisc, uint32_t rate2quantum); ----- .HTB Class Attributes Priority:: + [source,c] ----- uint32_t rtnl_htb_get_prio(struct rtnl_class *class); int rtnl_htb_set_prio(struct rtnl_class *class, uint32_t prio); ----- Rate:: The rate (bytes/s) specifies the maximum bandwidth an invidivual class can use without borrowing. The rate of a class should always be greater or erqual than the rate of its children. + [source,c] ----- uint32_t rtnl_htb_get_rate(struct rtnl_class *class); int rtnl_htb_set_rate(struct rtnl_class *class, uint32_t ceil); ----- Ceil Rate:: The ceil rate specifies the maximum bandwidth an invidivual class can use. This includes bandwidth that is being borrowed from other classes. Ceil defaults to the class rate implying that by default the class will not borrow. The ceil rate of a class should always be greater or erqual than the ceil rate of its children. + [source,c] ----- uint32_t rtnl_htb_get_ceil(struct rtnl_class *class); int rtnl_htb_set_ceil(struct rtnl_class *class, uint32_t ceil); ----- Burst:: TODO + [source,c] ----- uint32_t rtnl_htb_get_rbuffer(struct rtnl_class *class); int rtnl_htb_set_rbuffer(struct rtnl_class *class, uint32_t burst); ----- Ceil Burst:: TODO + [source,c] ----- uint32_t rtnl_htb_get_bbuffer(struct rtnl_class *class); int rtnl_htb_set_bbuffer(struct rtnl_class *class, uint32_t burst); ----- Quantum:: TODO + [source,c] ----- int rtnl_htb_set_quantum(struct rtnl_class *class, uint32_t quantum); ----- extern int rtnl_htb_set_cbuffer(struct rtnl_class *, uint32_t); [[tc_class]] === Class [options="header", cols="s,a,a,a,a"] |======================================================================= | | UNSPEC | TC_H_ROOT | 0:pY | pX:pY | UNSPEC 3+^| [horizontal] qdisc =:: root-qdisc class =:: root-qdisc:0 | [horizontal] qdisc =:: pX:0 class =:: pX:0 | 0:hY 3+^| [horizontal] qdisc =:: root-qdisc class =:: root-qdisc:hY | [horizontal] qdisc =:: pX:0 class =:: pX:hY | hX:hY 3+^| [horizontal] qdisc =:: hX: class =:: hX:hY | if pX != hX return -EINVAL [horizontal] qdisc =:: hX: class =:: hX:hY |======================================================================= [[tc_cls]] === Classifier (cls) TODO [[tc_classid_mngt]] === ClassID Management TODO [[tc_pktloc]] === Packet Location Aliasing (pktloc) TODO [[tc_api]] === Traffic Control Module API TODO