.TH IPQ_MESSAGE_TYPE 3 "16 October 2001" "Linux iptables 1.2" "Linux Programmer's Manual"
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.\"
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.\" Copyright (c) 2000-2001 Netfilter Core Team
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.\"
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.\" This program is free software; you can redistribute it and/or modify
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.\" it under the terms of the GNU General Public License as published by
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.\" the Free Software Foundation; either version 2 of the License, or
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.\" (at your option) any later version.
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.\"
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.\" This program is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public License
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.\" along with this program; if not, write to the Free Software
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.\" Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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.\"
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.\"
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.SH NAME
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ipq_message_type, ipq_get_packet, ipq_getmsgerr \(em query queue messages
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.SH SYNOPSIS
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.B #include <linux/netfilter.h>
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.br
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.B #include <libipq.h>
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.sp
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.BI "int ipq_message_type(const unsigned char *" buf ");"
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.br
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.BI "ipq_packet_msg_t *ipq_get_packet(const unsigned char *" buf ");"
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.br
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.BI "int ipq_get_msgerr(const unsigned char *" buf ");"
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.SH DESCRIPTION
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The
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.B ipq_message_type
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function returns the type of queue message returned to userspace
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via
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.BR ipq_read .
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.PP
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.B ipq_message_type
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should always be called following a successful call to
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.B ipq_read
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to determine whether the message is a packet message or an
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error message. The
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.I buf
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parameter should be the same data obtained from
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the previous call to
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.BR ipq_read .
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.PP
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.B ipq_message_type
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will return one of the following values:
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.TP
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.B NLMSG_ERROR
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An error message generated by the Netlink transport.
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.PP
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.TP
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.B IPQM_PACKET
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A packet message containing packet metadata and optional packet payload data.
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.PP
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The
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.B ipq_get_packet
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function should be called if
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.B ipq_message_type
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returns
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.BR IPQM_PACKET .
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The
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.I buf
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parameter should point to the same data used for the call to
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.BR ipq_message_type .
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The pointer returned by
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.B ipq_get_packet
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points to a packet message, which is declared as follows:
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.PP
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.RS
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.nf
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typedef struct ipq_packet_msg {
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unsigned long packet_id; /* ID of queued packet */
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unsigned long mark; /* Netfilter mark value */
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long timestamp_sec; /* Packet arrival time (seconds) */
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long timestamp_usec; /* Packet arrvial time (+useconds) */
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unsigned int hook; /* Netfilter hook we rode in on */
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char indev_name[IFNAMSIZ]; /* Name of incoming interface */
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char outdev_name[IFNAMSIZ]; /* Name of outgoing interface */
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unsigned short hw_protocol; /* Hardware protocol (network order) */
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unsigned short hw_type; /* Hardware type */
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unsigned char hw_addrlen; /* Hardware address length */
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unsigned char hw_addr[8]; /* Hardware address */
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size_t data_len; /* Length of packet data */
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unsigned char payload[0]; /* Optional packet data */
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} ipq_packet_msg_t;
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.fi
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.RE
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.PP
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Each of these fields may be read by the application. If the queue mode
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is
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.B IPQ_COPY_PACKET
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and the
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.I data_len
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value is greater than zero, the packet payload contents may be accessed
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in the memory following the
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.B ipq_packet_msg_t
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structure to a range of
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.I data_len.
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.PP
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The
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.I packet_id
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field contains a packet identifier to be used when calling
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.BR ipq_set_verdict .
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.PP
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The
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.B ipq_get_msgerr
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function should be called if
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.B ipq_message_type
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returns
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.BR NLMSG_ERROR.
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The
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.I buf
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parameter should point to the same data used for the call to
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.BR ipq_message_type .
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The value returned by
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.B ipq_get_msgerr
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is set by higher level kernel code and corresponds to standard
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.B errno
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values.
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.SH BUGS
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None known.
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.SH AUTHOR
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James Morris <jmorris@intercode.com.au>
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.SH COPYRIGHT
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Copyright (c) 2000-2001 Netfilter Core Team.
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.PP
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Distributed under the GNU General Public License.
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.SH SEE ALSO
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.BR iptables (8),
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.BR libipq (3).
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