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       ipq_message_type, ipq_get_packet, ipq_getmsgerr - query queue messages


       #include <linux/netfilter.h>
       #include <libipq.h>

       int ipq_message_type(const unsigned char *buf);
       ipq_packet_msg_t *ipq_get_packet(const unsigned char *buf);
       int ipq_get_msgerr(const unsigned char *buf);


       The  ipq_message_type  function  returns  the  type  of  queue  message
       returned to userspace via ipq_read.

       ipq_message_type should always be called following a successful call to
       ipq_read  to  determine  whether  the message is a packet message or an
       error message. The buf parameter should be the same data obtained  from
       the previous call to ipq_read.

       ipq_message_type will return one of the following values:

              An error message generated by the Netlink transport.

              A  packet message containing packet metadata and optional packet
              payload data.

       The  ipq_get_packet  function  should  be  called  if  ipq_message_type
       returns  IPQM_PACKET.   The buf parameter should point to the same data
       used for  the  call  to  ipq_message_type.   The  pointer  returned  by
       ipq_get_packet  points  to  a  packet  message,  which  is  declared as

              typedef struct ipq_packet_msg {
                   unsigned long packet_id;        /* ID of queued packet */
                   unsigned long mark;             /* Netfilter mark value */
                   long timestamp_sec;             /* Packet arrival time (seconds) */
                   long timestamp_usec;            /* Packet arrvial time (+useconds) */
                   unsigned int hook;              /* Netfilter hook we rode in on */
                   char indev_name[IFNAMSIZ];      /* Name of incoming interface */
                   char outdev_name[IFNAMSIZ];     /* Name of outgoing interface */
                   unsigned short hw_protocol;     /* Hardware protocol (network order) */
                   unsigned short hw_type;         /* Hardware type */
                   unsigned char hw_addrlen;       /* Hardware address length */
                   unsigned char hw_addr[8];       /* Hardware address */
                   size_t data_len;                /* Length of packet data */
                   unsigned char payload[0];       /* Optional packet data */
              } ipq_packet_msg_t;

       Each of these fields may be read by the application.  If the queue mode
       is  IPQ_COPY_PACKET  and  the  data_len value is greater than zero, the
       packet payload contents may be accessed in  the  memory  following  the
       ipq_packet_msg_t structure to a range of data_len.

       The  packet_id  field  contains  a  packet  identifier  to be used when
       calling ipq_set_verdict.

       The  ipq_get_msgerr  function  should  be  called  if  ipq_message_type
       returns  NLMSG_ERROR.   The buf parameter should point to the same data
       used  for  the  call  to  ipq_message_type.   The  value  returned   by
       ipq_get_msgerr  is  set  by higher level kernel code and corresponds to
       standard errno values.


       None known.


       James Morris <>


       Copyright (c) 2000-2001 Netfilter Core Team.

       Distributed under the GNU General Public License.


       iptables(8), libipq(3).