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);
}