libnl  1.1
Modules
Netfilter Netlink
Netlink Families

Modules

 Conntrack
 Log

Socket Creating

int nfnl_connect (struct nl_handle *handle)
 Create and connect netfilter netlink socket.

Sending

int nfnl_send_simple (struct nl_handle *handle, uint8_t subsys_id, uint8_t type, int flags, uint8_t family, uint16_t res_id)
 Send trivial netfilter netlink message.

Message Parsing

uint8_t nfnlmsg_subsys (struct nlmsghdr *nlh)
 Get netfilter subsystem id from message.
uint8_t nfnlmsg_subtype (struct nlmsghdr *nlh)
 Get netfilter message type from message.
uint8_t nfnlmsg_family (struct nlmsghdr *nlh)
 Get netfilter family from message.
uint16_t nfnlmsg_res_id (struct nlmsghdr *nlh)
 Get netfilter resource id from message.

Message Building

struct nl_msg * nfnlmsg_alloc_simple (uint8_t subsys_id, uint8_t type, int flags, uint8_t family, uint16_t res_id)
 Allocate a new netfilter netlink message.
int nfnlmsg_put (struct nl_msg *msg, uint32_t pid, uint32_t seq, uint8_t subsys_id, uint8_t type, int flags, uint8_t family, uint16_t res_id)
 Add netlink and netfilter netlink headers to netlink message.

Detailed Description

Message Format
<------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
+----------------------------+- - -+- - - - - - - - - - -+- - -+
| Header | Pad | Payload | Pad |
| struct nlmsghdr | | | |
+----------------------------+- - -+- - - - - - - - - - -+- - -+
<-------- NFNL_HDRLEN --------->
+--------------------------+- - -+------------+
| Netfilter Netlink Header | Pad | Attributes |
| struct nfgenmsg | | |
+--------------------------+- - -+------------+
nfnlmsg_attrdata(nfg, hdrlen)-----^
1) Creating a new netfilter netlink message
struct nl_msg *msg;
// Create a new empty netlink message
msg = nlmsg_alloc();
// Append the netlink and netfilter netlink message header
hdr = nfnlmsg_put(msg, PID, SEQ, SUBSYS, TYPE, NLM_F_ECHO,
FAMILY, RES_ID);
// Append the attributes.
nla_put_u32(msg, 1, 0x10);
// Message is ready to be sent.
nl_send_auto_complete(nl_handle, msg);
// All done? Free the message.
nlmsg_free(msg);
2) Sending of trivial messages
// For trivial messages not requiring any subsys specific header or
// attributes, nfnl_send_simple() may be used to send messages directly.
nfnl_send_simple(nl_handle, SUBSYS, TYPE, 0, FAMILY, RES_ID);

Function Documentation

int nfnl_connect ( struct nl_handle *  handle)
Parameters:
handleNetlink handle.

Creates a NETLINK_NETFILTER netlink socket, binds the socket and issues a connection attempt.

See also:
nl_connect()
Returns:
0 on success or a negative error code.

Definition at line 85 of file nfnl.c.

References nl_connect().

{
return nl_connect(handle, NETLINK_NETFILTER);
}
int nfnl_send_simple ( struct nl_handle *  handle,
uint8_t  subsys_id,
uint8_t  type,
int  flags,
uint8_t  family,
uint16_t  res_id 
)
Parameters:
handleNetlink handle.
subsys_idnfnetlink subsystem
typenfnetlink message type
flagsmessage flags
familynfnetlink address family
res_idnfnetlink resource id
Returns:
Newly allocated netlink message or NULL.

Definition at line 108 of file nfnl.c.

References nl_send_simple().

{
struct nfgenmsg hdr = {
.nfgen_family = family,
.version = NFNETLINK_V0,
.res_id = htons(res_id),
};
return nl_send_simple(handle, NFNLMSG_TYPE(subsys_id, type), flags,
&hdr, sizeof(hdr));
}
uint8_t nfnlmsg_subsys ( struct nlmsghdr nlh)
Parameters:
nlhnetlink messsage header

Definition at line 132 of file nfnl.c.

References nlmsghdr::nlmsg_type.

{
return NFNL_SUBSYS_ID(nlh->nlmsg_type);
}
uint8_t nfnlmsg_subtype ( struct nlmsghdr nlh)
Parameters:
nlhnetlink messsage header

Definition at line 141 of file nfnl.c.

References nlmsghdr::nlmsg_type.

{
return NFNL_MSG_TYPE(nlh->nlmsg_type);
}
uint8_t nfnlmsg_family ( struct nlmsghdr nlh)
Parameters:
nlhnetlink messsage header

Definition at line 150 of file nfnl.c.

References nlmsg_data().

{
struct nfgenmsg *nfg = nlmsg_data(nlh);
return nfg->nfgen_family;
}
uint16_t nfnlmsg_res_id ( struct nlmsghdr nlh)
Parameters:
nlhnetlink messsage header

Definition at line 161 of file nfnl.c.

References nlmsg_data().

{
struct nfgenmsg *nfg = nlmsg_data(nlh);
return ntohs(nfg->res_id);
}
struct nl_msg* nfnlmsg_alloc_simple ( uint8_t  subsys_id,
uint8_t  type,
int  flags,
uint8_t  family,
uint16_t  res_id 
)
read
Parameters:
subsys_idnfnetlink subsystem
typenfnetlink message type
flagsmessage flags
familynfnetlink address family
res_idnfnetlink resource id
Returns:
Newly allocated netlink message or NULL.

Definition at line 201 of file nfnl.c.

References nlmsg_alloc_simple(), and nlmsg_free().

{
struct nl_msg *msg;
msg = nlmsg_alloc_simple(NFNLMSG_TYPE(subsys_id, type), flags);
if (msg == NULL)
return NULL;
if (nfnlmsg_append(msg, family, res_id) < 0)
goto nla_put_failure;
return msg;
nla_put_failure:
nlmsg_free(msg);
return NULL;
}
int nfnlmsg_put ( struct nl_msg *  msg,
uint32_t  pid,
uint32_t  seq,
uint8_t  subsys_id,
uint8_t  type,
int  flags,
uint8_t  family,
uint16_t  res_id 
)
Parameters:
msgnetlink message
pidnetlink process id
seqsequence number of message
subsys_idnfnetlink subsystem
typenfnetlink message type
flagsmessage flags
familynfnetlink address family
res_idnfnetlink resource id

Definition at line 231 of file nfnl.c.

References nlmsg_put().

{
struct nlmsghdr *nlh;
nlh = nlmsg_put(msg, pid, seq, NFNLMSG_TYPE(subsys_id, type), 0, flags);
if (nlh == NULL)
return nl_get_errno();
return nfnlmsg_append(msg, family, res_id);
}