Message Construction & Parsing

Netlink Message Construction/Parsing Interface. More...

Modules
	Attributes
	Netlink Attributes Construction/Parsing Interface.

Macros
#define	NL_AUTO_PORT   0
	Will cause the netlink port to be set to the port assigned to the netlink icoket ust before sending the message off. More...
#define	NL_AUTO_SEQ   0
	May be used to refer to a sequence number which should be automatically set just before sending the message off. More...

Netlink Message Type Translations
char *	nl_nlmsgtype2str (int type, char *buf, size_t size)
int	nl_str2nlmsgtype (const char *name)

Size Calculations
int	nlmsg_size (int payload)
	Calculates size of netlink message based on payload length. More...
int	nlmsg_total_size (int payload)
	Calculates size of netlink message including padding based on payload length. More...
int	nlmsg_padlen (int payload)
	Size of padding that needs to be added at end of message. More...

Access to Message Payload
void *	nlmsg_data (const struct nlmsghdr *nlh)
	Return pointer to message payload. More...
void *	nlmsg_tail (const struct nlmsghdr *nlh)
int	nlmsg_datalen (const struct nlmsghdr *nlh)
	Return length of message payload. More...

Attribute Access
struct nlattr *	nlmsg_attrdata (const struct nlmsghdr *nlh, int hdrlen)
	head of attributes data More...
int	nlmsg_attrlen (const struct nlmsghdr *nlh, int hdrlen)
	length of attributes data More...

Message Parsing
int	nlmsg_valid_hdr (const struct nlmsghdr *nlh, int hdrlen)
int	nlmsg_ok (const struct nlmsghdr *nlh, int remaining)
	check if the netlink message fits into the remaining bytes More...
struct nlmsghdr *	nlmsg_next (struct nlmsghdr *nlh, int *remaining)
	next netlink message in message stream More...
int	nlmsg_parse (struct nlmsghdr *nlh, int hdrlen, struct nlattr *tb[], int maxtype, const struct nla_policy *policy)
	parse attributes of a netlink message More...
struct nlattr *	nlmsg_find_attr (struct nlmsghdr *nlh, int hdrlen, int attrtype)
	nlmsg_find_attr - find a specific attribute in a netlink message More...
int	nlmsg_validate (struct nlmsghdr *nlh, int hdrlen, int maxtype, const struct nla_policy *policy)
	nlmsg_validate - validate a netlink message including attributes More...

Message Building/Access
struct nl_msg *	nlmsg_alloc (void)
	Allocate a new netlink message with the default maximum payload size. More...
struct nl_msg *	nlmsg_alloc_size (size_t max)
	Allocate a new netlink message with maximum payload size specified. More...
struct nl_msg *	nlmsg_inherit (struct nlmsghdr *hdr)
	Allocate a new netlink message and inherit netlink message header. More...
struct nl_msg *	nlmsg_alloc_simple (int nlmsgtype, int flags)
	Allocate a new netlink message. More...
void	nlmsg_set_default_size (size_t max)
	Set the default maximum message payload size for allocated messages. More...
struct nl_msg *	nlmsg_convert (struct nlmsghdr *hdr)
	Convert a netlink message received from a netlink socket to a nl_msg. More...
void *	nlmsg_reserve (struct nl_msg *n, size_t len, int pad)
	Reserve room for additional data in a netlink message. More...
int	nlmsg_append (struct nl_msg *n, void *data, size_t len, int pad)
	Append data to tail of a netlink message. More...
int	nlmsg_expand (struct nl_msg *n, size_t newlen)
	Expand maximum payload size of a netlink message. More...
struct nlmsghdr *	nlmsg_put (struct nl_msg *n, uint32_t pid, uint32_t seq, int type, int payload, int flags)
	Add a netlink message header to a netlink message. More...
struct nlmsghdr *	nlmsg_hdr (struct nl_msg *n)
	Return actual netlink message. More...
void	nlmsg_get (struct nl_msg *msg)
	Acquire a reference on a netlink message. More...
void	nlmsg_free (struct nl_msg *msg)
	Release a reference from an netlink message. More...

Attributes
void	nlmsg_set_proto (struct nl_msg *msg, int protocol)
int	nlmsg_get_proto (struct nl_msg *msg)
size_t	nlmsg_get_max_size (struct nl_msg *msg)
void	nlmsg_set_src (struct nl_msg *msg, struct sockaddr_nl *addr)
struct sockaddr_nl *	nlmsg_get_src (struct nl_msg *msg)
void	nlmsg_set_dst (struct nl_msg *msg, struct sockaddr_nl *addr)
struct sockaddr_nl *	nlmsg_get_dst (struct nl_msg *msg)
void	nlmsg_set_creds (struct nl_msg *msg, struct ucred *creds)
struct ucred *	nlmsg_get_creds (struct nl_msg *msg)

Netlink Message Flags Translations
char *	nl_nlmsg_flags2str (int flags, char *buf, size_t len)

Direct Parsing
int	nl_msg_parse (struct nl_msg *msg, void(*cb)(struct nl_object *, void *), void *arg)

Dumping
void	nl_msg_dump (struct nl_msg *msg, FILE *ofd)
	Dump message in human readable format to file descriptor. More...

Iterators
#define	nlmsg_for_each_attr(pos, nlh, hdrlen, rem)
	Iterate over a stream of attributes in a message. More...
#define	nlmsg_for_each(pos, head, len)
	Iterate over a stream of messages. More...
#define	nlmsg_for_each_msg(pos, head, len, rem)    nlmsg_for_each(pos, head, len)

Detailed Description

Netlink Message Construction/Parsing Interface.

Related sections in the development guide:

• Message Parsing & Construction (Netlink Core Library Development Guide)

Header

#include <netlink/msg.h>

Macro Definition Documentation

NL_AUTO_PORT

#define NL_AUTO_PORT   0

Will cause the netlink port to be set to the port assigned to the netlink icoket ust before sending the message off.

Note

Requires the use of nl_send_auto()!

Definition at line 29 of file msg.h.

NL_AUTO_SEQ

#define NL_AUTO_SEQ   0

May be used to refer to a sequence number which should be automatically set just before sending the message off.

Note

Requires the use of nl_send_auto()!

Definition at line 40 of file msg.h.

nlmsg_for_each_attr

#define nlmsg_for_each_attr	(		pos,
			nlh,
			hdrlen,
			rem
	)

Value:

        nla_for_each_attr(pos, nlmsg_attrdata(nlh, hdrlen), \
                          nlmsg_attrlen(nlh, hdrlen), rem)

Iterate over a stream of attributes in a message.

Parameters

pos	loop counter, set to current attribute
nlh	netlink message header
hdrlen	length of family header
rem	initialized to len, holds bytes currently remaining in stream

Definition at line 119 of file msg.h.

nlmsg_for_each

#define nlmsg_for_each	(		pos,
			head,
			len
	)

Value:

        for (int rem = len, pos = head; \
                nlmsg_ok(pos, rem); \
                pos = nlmsg_next(pos, &rem))

Iterate over a stream of messages.

Parameters

pos	loop counter, set to current message
head	head of message stream
len	length of message stream

Definition at line 129 of file msg.h.

nlmsg_for_each_msg

#define nlmsg_for_each_msg	(		pos,
			head,
			len,
			rem
	)		nlmsg_for_each(pos, head, len)

Definition at line 134 of file msg.h.

Function Documentation

nlmsg_size()

int nlmsg_size

(

int

payload

)

Calculates size of netlink message based on payload length.

Parameters

payload

Length of payload

Returns

size of netlink message without padding.

Definition at line 49 of file msg.c.

nlmsg_total_size()

int nlmsg_total_size

(

int

payload

)

Calculates size of netlink message including padding based on payload length.

Parameters

payload

Length of payload

This function is idential to nlmsg_size() + nlmsg_padlen().

Returns

Size of netlink message including padding.

Definition at line 67 of file msg.c.

Referenced by nlmsg_padlen(), and nlmsg_set_default_size().

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nlmsg_padlen()

int nlmsg_padlen

(

int

payload

)

Size of padding that needs to be added at end of message.

Parameters

payload

Length of payload

Calculates the number of bytes of padding which is required to be added to the end of the message to ensure that the next netlink message header begins properly aligned to NLMSG_ALIGNTO.

Returns

Number of bytes of padding needed.

Definition at line 82 of file msg.c.

References nlmsg_total_size().

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nlmsg_data()

void * nlmsg_data

(

const struct nlmsghdr *

nlh

)

Return pointer to message payload.

Parameters

nlh	Netlink message header

Returns

Pointer to start of message payload.

Definition at line 100 of file msg.c.

Referenced by genlmsg_hdr(), genlmsg_parse(), genlmsg_put(), genlmsg_valid_hdr(), genlmsg_validate(), nfnlmsg_family(), nfnlmsg_res_id(), nla_put(), nla_put_nested(), nla_reserve(), and nlmsg_attrdata().

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nlmsg_tail()

void * nlmsg_tail

(

const struct nlmsghdr *

nlh

)

Definition at line 105 of file msg.c.

nlmsg_datalen()

int nlmsg_datalen

(

const struct nlmsghdr *

nlh

)

Return length of message payload.

Parameters

nlh	Netlink message header

Returns

Length of message payload in bytes.

Definition at line 116 of file msg.c.

Referenced by nla_put_nested().

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nlmsg_attrdata()

struct nlattr * nlmsg_attrdata	(	const struct nlmsghdr *	nlh,
		int	hdrlen
	)

head of attributes data

Parameters

nlh	netlink message header
hdrlen	length of family specific header

Definition at line 138 of file msg.c.

References nlmsg_data().

Referenced by nlmsg_find_attr(), nlmsg_parse(), and nlmsg_validate().

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nlmsg_attrlen()

int nlmsg_attrlen	(	const struct nlmsghdr *	nlh,
		int	hdrlen
	)

length of attributes data

Parameters

nlh	netlink message header
hdrlen	length of family specific header

Definition at line 149 of file msg.c.

Referenced by nlmsg_find_attr(), nlmsg_parse(), and nlmsg_validate().

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nlmsg_valid_hdr()

int nlmsg_valid_hdr	(	const struct nlmsghdr *	nlh,
		int	hdrlen
	)

Definition at line 161 of file msg.c.

nlmsg_ok()

int nlmsg_ok	(	const struct nlmsghdr *	nlh,
		int	remaining
	)

check if the netlink message fits into the remaining bytes

Parameters

nlh	netlink message header
remaining	number of bytes remaining in message stream

Definition at line 174 of file msg.c.

nlmsg_next()

struct nlmsghdr * nlmsg_next	(	struct nlmsghdr *	nlh,
		int *	remaining
	)

next netlink message in message stream

Parameters

nlh	netlink message header
remaining	number of bytes remaining in message stream

Returns

the next netlink message in the message stream and decrements remaining by the size of the current message.

Definition at line 189 of file msg.c.

nlmsg_parse()

int nlmsg_parse	(	struct nlmsghdr *	nlh,
		int	hdrlen,
		struct nlattr *	tb[],
		int	maxtype,
		const struct nla_policy *	policy
	)

parse attributes of a netlink message

Parameters

nlh	netlink message header
hdrlen	length of family specific header
tb	destination array with maxtype+1 elements
maxtype	maximum attribute type to be expected
policy	validation policy

See nla_parse()

Definition at line 208 of file msg.c.

References nla_parse(), nlmsg_attrdata(), and nlmsg_attrlen().

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nlmsg_find_attr()

struct nlattr * nlmsg_find_attr	(	struct nlmsghdr *	nlh,
		int	hdrlen,
		int	attrtype
	)

nlmsg_find_attr - find a specific attribute in a netlink message

Parameters

nlh	netlink message header
hdrlen	length of familiy specific header
attrtype	type of attribute to look for

Returns the first attribute which matches the specified type.

Definition at line 226 of file msg.c.

References nla_find(), nlmsg_attrdata(), and nlmsg_attrlen().

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nlmsg_validate()

int nlmsg_validate	(	struct nlmsghdr *	nlh,
		int	hdrlen,
		int	maxtype,
		const struct nla_policy *	policy
	)

nlmsg_validate - validate a netlink message including attributes

Parameters

nlh	netlinket message header
hdrlen	length of familiy specific header
maxtype	maximum attribute type to be expected
policy	validation policy

Definition at line 239 of file msg.c.

References nla_validate(), nlmsg_attrdata(), and nlmsg_attrlen().

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nlmsg_alloc()

struct nl_msg * nlmsg_alloc

(

void

)

Allocate a new netlink message with the default maximum payload size.

Allocates a new netlink message without any further payload. The maximum payload size defaults to PAGESIZE or as otherwise specified with nlmsg_set_default_size().

Returns

Newly allocated netlink message or NULL.

Definition at line 294 of file msg.c.

Referenced by nlmsg_inherit(), and rtnl_neightbl_build_change_request().

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nlmsg_alloc_size()

struct nl_msg * nlmsg_alloc_size

(

size_t

max

)

Allocate a new netlink message with maximum payload size specified.

Definition at line 302 of file msg.c.

nlmsg_inherit()

struct nl_msg * nlmsg_inherit

(

struct nlmsghdr *

hdr

)

Allocate a new netlink message and inherit netlink message header.

Parameters

hdr	Netlink message header template

Allocates a new netlink message and inherits the original message header. If hdr is not NULL it will be used as a template for the netlink message header, otherwise the header is left blank.

Returns

Newly allocated netlink message or NULL

Definition at line 317 of file msg.c.

References nlmsg_alloc().

Referenced by nlmsg_alloc_simple().

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nlmsg_alloc_simple()

struct nl_msg * nlmsg_alloc_simple	(	int	nlmsgtype,
		int	flags
	)

Allocate a new netlink message.

Parameters

nlmsgtype	Netlink message type
flags	Message flags.

Returns

Newly allocated netlink message or NULL.

Definition at line 341 of file msg.c.

References NL_AUTO_SEQ, and nlmsg_inherit().

Referenced by flnl_lookup_build_request(), nfnlmsg_alloc_simple(), nl_send_simple(), rtnl_class_build_delete_request(), rtnl_link_build_delete_request(), rtnl_link_build_get_request(), rtnl_neightbl_build_change_request(), and rtnl_qdisc_build_delete_request().

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nlmsg_set_default_size()

void nlmsg_set_default_size

(

size_t

max

)

Set the default maximum message payload size for allocated messages.

Parameters

max	Size of payload in bytes.

Definition at line 362 of file msg.c.

References nlmsg_total_size().

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nlmsg_convert()

struct nl_msg * nlmsg_convert

(

struct nlmsghdr *

hdr

)

Convert a netlink message received from a netlink socket to a nl_msg.

Parameters

hdr	Netlink message received from netlink socket.

Allocates a new netlink message and copies all of the data pointed to by hdr into the new message object.

Returns

Newly allocated netlink message or NULL.

Definition at line 379 of file msg.c.

nlmsg_reserve()

void * nlmsg_reserve	(	struct nl_msg *	n,
		size_t	len,
		int	pad
	)

Reserve room for additional data in a netlink message.

Parameters

n	netlink message
len	length of additional data to reserve room for
pad	number of bytes to align data to

Reserves room for additional data at the tail of the an existing netlink message. Eventual padding required will be zeroed out.

Returns

Pointer to start of additional data tailroom or NULL.

Definition at line 404 of file msg.c.

Referenced by nlmsg_append(), and nlmsg_put().

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nlmsg_append()

int nlmsg_append	(	struct nl_msg *	n,
		void *	data,
		size_t	len,
		int	pad
	)

Append data to tail of a netlink message.

Parameters

n	netlink message
data	data to add
len	length of data
pad	Number of bytes to align data to.

Extends the netlink message as needed and appends the data of given length to the message.

Returns

0 on success or a negative error code

Definition at line 442 of file msg.c.

References nlmsg_reserve().

Referenced by flnl_lookup_build_request(), nl_send_simple(), rtnl_class_build_delete_request(), rtnl_link_build_delete_request(), rtnl_link_build_get_request(), rtnl_neightbl_build_change_request(), and rtnl_qdisc_build_delete_request().

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nlmsg_expand()

int nlmsg_expand	(	struct nl_msg *	n,
		size_t	newlen
	)

Expand maximum payload size of a netlink message.

Parameters

n	Netlink message.
newlen	New maximum payload size.

Reallocates the payload section of a netlink message and increases the maximum payload size of the message.

Note

Any pointers pointing to old payload block will be stale and need to be refetched. Therfore, do not expand while constructing nested attributes or while reserved data blocks are held.

Returns

0 on success or a negative error code.

Definition at line 470 of file msg.c.

nlmsg_put()

struct nlmsghdr * nlmsg_put	(	struct nl_msg *	n,
		uint32_t	pid,
		uint32_t	seq,
		int	type,
		int	payload,
		int	flags
	)

Add a netlink message header to a netlink message.

Parameters

n	netlink message
pid	netlink process id or NL_AUTO_PID
seq	sequence number of message or NL_AUTO_SEQ
type	message type
payload	length of message payload
flags	message flags

Adds or overwrites the netlink message header in an existing message object. If payload is greater-than zero additional room will be reserved, f.e. for family specific headers. It can be accesed via nlmsg_data().

Returns

A pointer to the netlink message header or NULL.

Definition at line 503 of file msg.c.

References nlmsg_reserve().

Referenced by genlmsg_put(), and nfnlmsg_put().

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nlmsg_hdr()

struct nlmsghdr * nlmsg_hdr

(

struct nl_msg *

n

)

Return actual netlink message.

Parameters

n	netlink message

Returns the actual netlink message casted to the type of the netlink message header.

Returns

A pointer to the netlink message.

Definition at line 536 of file msg.c.

Referenced by genl_handle_msg(), nl_cache_parse_and_add(), nl_complete_msg(), nl_msg_dump(), and nl_send().

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nlmsg_get()

void nlmsg_get

(

struct nl_msg *

msg

)

Acquire a reference on a netlink message.

Parameters

msg	message to acquire reference from

Definition at line 545 of file msg.c.

nlmsg_free()

void nlmsg_free

(

struct nl_msg *

msg

)

Release a reference from an netlink message.

Parameters

msg	message to release reference from

Frees memory after the last reference has been released.

Definition at line 558 of file msg.c.

Referenced by flnl_lookup(), flnl_lookup_build_request(), nfnlmsg_alloc_simple(), nl_send_simple(), nl_send_sync(), rtnl_addr_add(), rtnl_addr_delete(), rtnl_class_build_delete_request(), rtnl_neigh_add(), rtnl_neigh_delete(), rtnl_neightbl_build_change_request(), rtnl_neightbl_change(), rtnl_qdisc_build_delete_request(), rtnl_rule_add(), and rtnl_rule_delete().

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nlmsg_set_proto()

void nlmsg_set_proto	(	struct nl_msg *	msg,
		int	protocol
	)

Definition at line 584 of file msg.c.

nlmsg_get_proto()

int nlmsg_get_proto

(

struct nl_msg *

msg

)

Definition at line 589 of file msg.c.

nlmsg_get_max_size()

size_t nlmsg_get_max_size

(

struct nl_msg *

msg

)

Definition at line 594 of file msg.c.

nlmsg_set_src()

void nlmsg_set_src	(	struct nl_msg *	msg,
		struct sockaddr_nl *	addr
	)

Definition at line 599 of file msg.c.

nlmsg_get_src()

struct sockaddr_nl * nlmsg_get_src

(

struct nl_msg *

msg

)

Definition at line 604 of file msg.c.

nlmsg_set_dst()

void nlmsg_set_dst	(	struct nl_msg *	msg,
		struct sockaddr_nl *	addr
	)

Definition at line 609 of file msg.c.

nlmsg_get_dst()

struct sockaddr_nl * nlmsg_get_dst

(

struct nl_msg *

msg

)

Definition at line 614 of file msg.c.

nlmsg_set_creds()

void nlmsg_set_creds	(	struct nl_msg *	msg,
		struct ucred *	creds
	)

Definition at line 619 of file msg.c.

nlmsg_get_creds()

struct ucred * nlmsg_get_creds

(

struct nl_msg *

msg

)

Definition at line 625 of file msg.c.

nl_nlmsgtype2str()

char * nl_nlmsgtype2str	(	int	type,
		char *	buf,
		size_t	size
	)

Definition at line 646 of file msg.c.

nl_str2nlmsgtype()

int nl_str2nlmsgtype

(

const char *

name

)

Definition at line 652 of file msg.c.

nl_nlmsg_flags2str()

char * nl_nlmsg_flags2str	(	int	flags,
		char *	buf,
		size_t	len
	)

Definition at line 664 of file msg.c.

nl_msg_parse()

int nl_msg_parse	(	struct nl_msg *	msg,
		void(*)(struct nl_object *, void *)	cb,
		void *	arg
	)

Definition at line 720 of file msg.c.

nl_msg_dump()

void nl_msg_dump	(	struct nl_msg *	msg,
		FILE *	ofd
	)

Dump message in human readable format to file descriptor.

Parameters

msg	Message to print
ofd	File descriptor.

Definition at line 969 of file msg.c.

References nlmsg_hdr().

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