Links (Interfaces)

Modules
	Link Info API

Macros
#define	RTNL_LINK_NOT_FOUND   -1
	Special interface index stating the link was not found.

Allocation/Freeing
struct rtnl_link *	rtnl_link_alloc (void)
void	rtnl_link_put (struct rtnl_link *link)

Cache Management
struct nl_cache *	rtnl_link_alloc_cache (struct nl_handle *handle)
	Allocate link cache and fill in all configured links. More...
struct rtnl_link *	rtnl_link_get (struct nl_cache *cache, int ifindex)
	Look up link by interface index in the provided cache. More...
struct rtnl_link *	rtnl_link_get_by_name (struct nl_cache *cache, const char *name)
	Look up link by link name in the provided cache. More...

Link Modifications
struct nl_msg *	rtnl_link_build_change_request (struct rtnl_link *old, struct rtnl_link *tmpl, int flags)
	Builds a netlink change request message to change link attributes. More...
int	rtnl_link_change (struct nl_handle *handle, struct rtnl_link *old, struct rtnl_link *tmpl, int flags)
	Change link attributes. More...

Name <-> Index Translations
char *	rtnl_link_i2name (struct nl_cache *cache, int ifindex, char *dst, size_t len)
	Translate an interface index to the corresponding link name. More...
int	rtnl_link_name2i (struct nl_cache *cache, const char *name)
	Translate a link name to the corresponding interface index. More...

Link Flags Translations
char *	rtnl_link_flags2str (int flags, char *buf, size_t len)
int	rtnl_link_str2flags (const char *name)

Link Statistics Translations
char *	rtnl_link_stat2str (int st, char *buf, size_t len)
int	rtnl_link_str2stat (const char *name)

Link Operstate Translations
char *	rtnl_link_operstate2str (int st, char *buf, size_t len)
int	rtnl_link_str2operstate (const char *name)

Link Mode Translations
char *	rtnl_link_mode2str (int st, char *buf, size_t len)
int	rtnl_link_str2mode (const char *name)

Attributes
void	rtnl_link_set_qdisc (struct rtnl_link *link, const char *qdisc)
char *	rtnl_link_get_qdisc (struct rtnl_link *link)
void	rtnl_link_set_name (struct rtnl_link *link, const char *name)
char *	rtnl_link_get_name (struct rtnl_link *link)
void	rtnl_link_set_addr (struct rtnl_link *link, struct nl_addr *addr)
struct nl_addr *	rtnl_link_get_addr (struct rtnl_link *link)
void	rtnl_link_set_broadcast (struct rtnl_link *link, struct nl_addr *brd)
struct nl_addr *	rtnl_link_get_broadcast (struct rtnl_link *link)
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)
void	rtnl_link_set_family (struct rtnl_link *link, int family)
int	rtnl_link_get_family (struct rtnl_link *link)
void	rtnl_link_set_arptype (struct rtnl_link *link, unsigned int arptype)
unsigned int	rtnl_link_get_arptype (struct rtnl_link *link)
void	rtnl_link_set_ifindex (struct rtnl_link *link, int ifindex)
int	rtnl_link_get_ifindex (struct rtnl_link *link)
void	rtnl_link_set_mtu (struct rtnl_link *link, unsigned int mtu)
unsigned int	rtnl_link_get_mtu (struct rtnl_link *link)
void	rtnl_link_set_txqlen (struct rtnl_link *link, unsigned int txqlen)
unsigned int	rtnl_link_get_txqlen (struct rtnl_link *link)
void	rtnl_link_set_weight (struct rtnl_link *link, unsigned int weight)
unsigned int	rtnl_link_get_weight (struct rtnl_link *link)
void	rtnl_link_set_link (struct rtnl_link *link, int ifindex)
int	rtnl_link_get_link (struct rtnl_link *link)
void	rtnl_link_set_master (struct rtnl_link *link, int ifindex)
int	rtnl_link_get_master (struct rtnl_link *link)
void	rtnl_link_set_operstate (struct rtnl_link *link, uint8_t operstate)
uint8_t	rtnl_link_get_operstate (struct rtnl_link *link)
void	rtnl_link_set_linkmode (struct rtnl_link *link, uint8_t linkmode)
uint8_t	rtnl_link_get_linkmode (struct rtnl_link *link)
uint64_t	rtnl_link_get_stat (struct rtnl_link *link, int id)
int	rtnl_link_set_info_type (struct rtnl_link *link, const char *type)
	Specify the info type of a link. More...
char *	rtnl_link_get_info_type (struct rtnl_link *link)
	Return info type of a link. More...

Detailed Description

Link Identification

A link can be identified by either its interface index or by its name. The kernel favours the interface index but falls back to the interface name if the interface index is lesser-than 0 for kernels >= 2.6.11. Therefore you can request changes without mapping a interface name to the corresponding index first.

Changeable Attributes

• Link layer address
• Link layer broadcast address
• device mapping (ifmap) (>= 2.6.9)
• MTU (>= 2.6.9)
• Transmission queue length (>= 2.6.9)
• Weight (>= 2.6.9)
• Link name (only via access through interface index) (>= 2.6.9)
• Flags (>= 2.6.9)
  • IFF_DEBUG
  • IFF_NOTRAILERS
  • IFF_NOARP
  • IFF_DYNAMIC
  • IFF_MULTICAST
  • IFF_PORTSEL
  • IFF_AUTOMEDIA
  • IFF_UP
  • IFF_PROMISC
  • IFF_ALLMULTI

Link Flags (linux/if.h)

IFF_UP            Status of link (up|down)
IFF_BROADCAST     Indicates this link allows broadcasting
IFF_MULTICAST     Indicates this link allows multicasting
IFF_ALLMULTI      Indicates this link is doing multicast routing
IFF_DEBUG         Tell the driver to do debugging (currently unused)
IFF_LOOPBACK      This is the loopback link
IFF_POINTOPOINT   Point-to-point link
IFF_NOARP         Link is unable to perform ARP
IFF_PROMISC       Status of promiscious mode flag
IFF_MASTER        Used by teql
IFF_SLAVE         Used by teql
IFF_PORTSEL       Indicates this link allows port selection
IFF_AUTOMEDIA     Indicates this link selects port automatically
IFF_DYNAMIC       Indicates the address of this link is dynamic
IFF_RUNNING       Link is running and carrier is ok.
IFF_NOTRAILERS    Unused, BSD compat.

Notes on IFF_PROMISC and IFF_ALLMULTI flags

Although you can query the status of IFF_PROMISC and IFF_ALLMULTI they do not represent the actual state in the kernel but rather whether the flag has been enabled/disabled by userspace. The link may be in promiscious mode even if IFF_PROMISC is not set in a link dump request response because promiscity might be needed by the driver for a period of time.

Note

The unit of the transmission queue length depends on the link type, a common unit is packets.

1) Retrieving information about available links

// The first step is to retrieve a list of all available interfaces within
// the kernel and put them into a cache.
struct nl_cache *cache = rtnl_link_alloc_cache(nl_handle);
 
// In a second step, a specific link may be looked up by either interface
// index or interface name.
struct rtnl_link *link = rtnl_link_get_by_name(cache, "lo");
 
// rtnl_link_get_by_name() is the short version for translating the
// interface name to an interface index first like this:
int ifindex = rtnl_link_name2i(cache, "lo");
struct rtnl_link *link = rtnl_link_get(cache, ifindex);
 
// After successful usage, the object must be given back to the cache
rtnl_link_put(link);

2) Changing link attributes

// In order to change any attributes of an existing link, we must allocate
// a new link to hold the change requests:
struct rtnl_link *request = rtnl_link_alloc();
 
// Now we can go on and specify the attributes we want to change:
rtnl_link_set_weight(request, 300);
rtnl_link_set_mtu(request, 1360);
 
// We can also shut an interface down administratively
rtnl_link_unset_flags(request, rtnl_link_str2flags("up"));
 
// Actually, we should know which link to change, so let's look it up
struct rtnl_link *old = rtnl_link_get(cache, "eth0");
 
// Two ways exist to commit this change request, the first one is to
// build the required netlink message and send it out in one single
// step:
rtnl_link_change(nl_handle, old, request);
 
// An alternative way is to build the netlink message and send it
// out yourself using nl_send_auto_complete()
struct nl_msg *msg = rtnl_link_build_change_request(old, request);
nl_send_auto_complete(nl_handle, nlmsg_hdr(msg));
nlmsg_free(msg);
 
// Don't forget to give back the link object ;->
rtnl_link_put(old);

3) Link Type Specific Attributes

// Some link types offer additional parameters and statistics specific
// to their type. F.e. a VLAN link can be configured like this:
//
// Allocate a new link and set the info type to "vlan". This is required
// to prepare the link to hold vlan specific attributes.
struct rtnl_link *request = rtnl_link_alloc();
rtnl_link_set_info_type(request, "vlan");
 
// Now vlan specific attributes can be set:
rtnl_link_vlan_set_id(request, 10);
rtnl_link_vlan_set_ingress_map(request, 2, 8);
 
// Of course the attributes can also be read, check the info type
// to make sure you are using the right access functions:
char *type = rtnl_link_get_info_type(link);
if (!strcmp(type, "vlan"))
        int id = rtnl_link_vlan_get_id(link);

Function Documentation

rtnl_link_alloc_cache()

struct nl_cache* rtnl_link_alloc_cache

(

struct nl_handle *

handle

)

Parameters

handle

Netlink handle.

Allocates a new link cache, initializes it properly and updates it to include all links currently configured in the kernel.

Note

Free the memory after usage.

Returns

Newly allocated cache or NULL if an error occured.

Definition at line 869 of file link.c.

{
        struct nl_cache * cache;
        
        cache = nl_cache_alloc(&rtnl_link_ops);
        if (cache == NULL)
                return NULL;
        
        if (handle && nl_cache_refill(handle, cache) < 0) {
                nl_cache_free(cache);
                return NULL;
        }
 
        return cache;
}

References nl_cache_alloc().

rtnl_link_get()

struct rtnl_link* rtnl_link_get	(	struct nl_cache *	cache,
		int	ifindex
	)

Parameters

cache	link cache
ifindex	link interface index

The caller owns a reference on the returned object and must give the object back via rtnl_link_put().

Returns

pointer to link inside the cache or NULL if no match was found.

Definition at line 895 of file link.c.

{
        struct rtnl_link *link;
 
        if (cache->c_ops != &rtnl_link_ops)
                return NULL;
 
        nl_list_for_each_entry(link, &cache->c_items, ce_list) {
                if (link->l_index == ifindex) {
                        nl_object_get((struct nl_object *) link);
                        return link;
                }
        }
 
        return NULL;
}

Referenced by rtnl_link_i2name().

rtnl_link_get_by_name()

struct rtnl_link* rtnl_link_get_by_name	(	struct nl_cache *	cache,
		const char *	name
	)

Parameters

cache	link cache
name	link name

The caller owns a reference on the returned object and must give the object back via rtnl_link_put().

Returns

pointer to link inside the cache or NULL if no match was found.

Definition at line 922 of file link.c.

{
        struct rtnl_link *link;
 
        if (cache->c_ops != &rtnl_link_ops)
                return NULL;
 
        nl_list_for_each_entry(link, &cache->c_items, ce_list) {
                if (!strcmp(name, link->l_name)) {
                        nl_object_get((struct nl_object *) link);
                        return link;
                }
        }
 
        return NULL;
}

Referenced by rtnl_link_name2i().

rtnl_link_build_change_request()

struct nl_msg* rtnl_link_build_change_request	(	struct rtnl_link *	old,
		struct rtnl_link *	tmpl,
		int	flags
	)

Parameters

old	link to be changed
tmpl	template with requested changes
flags	additional netlink message flags

Builds a new netlink message requesting a change of link attributes. The netlink message header isn't fully equipped with all relevant fields and must be sent out via nl_send_auto_complete() or supplemented as needed. old must point to a link currently configured in the kernel and tmpl must contain the attributes to be changed set via rtnl_link_set_* functions.

Returns

New netlink message

Note

Not all attributes can be changed, see Changeable Attributes for more details.

Definition at line 965 of file link.c.

{
        struct nl_msg *msg;
        struct ifinfomsg ifi = {
                .ifi_family = old->l_family,
                .ifi_index = old->l_index,
        };
 
        if (tmpl->ce_mask & LINK_ATTR_FLAGS) {
                ifi.ifi_flags = old->l_flags & ~tmpl->l_flag_mask;
                ifi.ifi_flags |= tmpl->l_flags;
        }
 
        msg = nlmsg_alloc_simple(RTM_SETLINK, flags);
        if (!msg)
                goto nla_put_failure;
 
        if (nlmsg_append(msg, &ifi, sizeof(ifi), NLMSG_ALIGNTO) < 0)
                goto nla_put_failure;
 
        if (tmpl->ce_mask & LINK_ATTR_ADDR)
                NLA_PUT_ADDR(msg, IFLA_ADDRESS, tmpl->l_addr);
 
        if (tmpl->ce_mask & LINK_ATTR_BRD)
                NLA_PUT_ADDR(msg, IFLA_BROADCAST, tmpl->l_bcast);
 
        if (tmpl->ce_mask & LINK_ATTR_MTU)
                NLA_PUT_U32(msg, IFLA_MTU, tmpl->l_mtu);
 
        if (tmpl->ce_mask & LINK_ATTR_TXQLEN)
                NLA_PUT_U32(msg, IFLA_TXQLEN, tmpl->l_txqlen);
 
        if (tmpl->ce_mask & LINK_ATTR_WEIGHT)
                NLA_PUT_U32(msg, IFLA_WEIGHT, tmpl->l_weight);
 
        if (tmpl->ce_mask & LINK_ATTR_IFNAME)
                NLA_PUT_STRING(msg, IFLA_IFNAME, tmpl->l_name);
 
        if (tmpl->ce_mask & LINK_ATTR_OPERSTATE)
                NLA_PUT_U8(msg, IFLA_OPERSTATE, tmpl->l_operstate);
 
        if (tmpl->ce_mask & LINK_ATTR_LINKMODE)
                NLA_PUT_U8(msg, IFLA_LINKMODE, tmpl->l_linkmode);
 
        if ((tmpl->ce_mask & LINK_ATTR_LINKINFO) && tmpl->l_info_ops &&
            tmpl->l_info_ops->io_put_attrs) {
                struct nlattr *info;
 
                if (!(info = nla_nest_start(msg, IFLA_LINKINFO)))
                        goto nla_put_failure;
 
                NLA_PUT_STRING(msg, IFLA_INFO_KIND, tmpl->l_info_ops->io_name);
 
                if (tmpl->l_info_ops->io_put_attrs(msg, tmpl) < 0)
                        goto nla_put_failure;
 
                nla_nest_end(msg, info);
        }
 
        return msg;
 
nla_put_failure:
        nlmsg_free(msg);
        return NULL;
}

References nla_nest_end(), nla_nest_start(), NLA_PUT_ADDR, NLA_PUT_STRING, NLA_PUT_U32, NLA_PUT_U8, nlmsg_alloc_simple(), nlmsg_append(), and nlmsg_free().

Referenced by rtnl_link_change().

rtnl_link_change()

int rtnl_link_change	(	struct nl_handle *	handle,
		struct rtnl_link *	old,
		struct rtnl_link *	tmpl,
		int	flags
	)

Parameters

handle	netlink handle
old	link to be changed
tmpl	template with requested changes
flags	additional netlink message flags

Builds a new netlink message by calling rtnl_link_build_change_request(), sends the request to the kernel and waits for the next ACK to be received, i.e. blocks until the request has been processed.

Returns

0 on success or a negative error code

Note

Not all attributes can be changed, see Changeable Attributes for more details.

Definition at line 1048 of file link.c.

{
        int err;
        struct nl_msg *msg;
        
        msg = rtnl_link_build_change_request(old, tmpl, flags);
        if (!msg)
                return nl_errno(ENOMEM);
        
        err = nl_send_auto_complete(handle, msg);
        nlmsg_free(msg);
        if (err < 0)
                return err;
 
        return nl_wait_for_ack(handle);
}

References nl_send_auto_complete(), nl_wait_for_ack(), nlmsg_free(), and rtnl_link_build_change_request().

rtnl_link_i2name()

char* rtnl_link_i2name	(	struct nl_cache *	cache,
		int	ifindex,
		char *	dst,
		size_t	len
	)

Parameters

cache	link cache
ifindex	link interface index
dst	destination buffer
len	length of destination buffer

Translates the specified interface index to the corresponding link name and stores the name in the destination buffer.

Returns

link name or NULL if no match was found.

Definition at line 1085 of file link.c.

{
        struct rtnl_link *link = rtnl_link_get(cache, ifindex);
 
        if (link) {
                strncpy(dst, link->l_name, len - 1);
                rtnl_link_put(link);
                return dst;
        }
 
        return NULL;
}

References rtnl_link_get().

rtnl_link_name2i()

int rtnl_link_name2i	(	struct nl_cache *	cache,
		const char *	name
	)

Parameters

cache	link cache
name	link name

Returns

interface index or RTNL_LINK_NOT_FOUND if no match was found.

Definition at line 1106 of file link.c.

{
        int ifindex = RTNL_LINK_NOT_FOUND;
        struct rtnl_link *link;
        
        link = rtnl_link_get_by_name(cache, name);
        if (link) {
                ifindex = link->l_index;
                rtnl_link_put(link);
        }
 
        return ifindex;
}

References rtnl_link_get_by_name(), and RTNL_LINK_NOT_FOUND.

rtnl_link_set_info_type()

int rtnl_link_set_info_type	(	struct rtnl_link *	link,
		const char *	type
	)

Parameters

link	link object
type	info type

Looks up the info type and prepares the link to store info type specific attributes. If an info type has been assigned already it will be released with all changes lost.

Returns

0 on success or a negative errror code.

Definition at line 1501 of file link.c.

{
        struct rtnl_link_info_ops *io;
        int err;
 
        if ((io = rtnl_link_info_ops_lookup(type)) == NULL)
                return nl_error(ENOENT, "No such link info type exists");
 
        if (link->l_info_ops)
                release_link_info(link);
 
        if ((err = io->io_alloc(link)) < 0)
                return err;
 
        link->l_info_ops = io;
 
        return 0;
}

rtnl_link_get_info_type()

char* rtnl_link_get_info_type

(

struct rtnl_link *

link

)

Parameters

link	link object

Note

The returned pointer is only valid as long as the link exists

Returns

Info type name or NULL if unknown.

Definition at line 1527 of file link.c.

{
        if (link->l_info_ops)
                return link->l_info_ops->io_name;
        else
                return NULL;
}