.TH IPQ_MESSAGE_TYPE 3 "16 October 2001" "Linux iptables 1.2" "Linux Programmer's Manual" 

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.SH NAME

ipq_message_type, ipq_get_packet, ipq_getmsgerr \(em query queue messages

.SH SYNOPSIS

.B #include <linux/netfilter.h>

.br

.B #include <libipq.h>

.sp

.BI "int ipq_message_type(const unsigned char *" buf ");"

.br

.BI "ipq_packet_msg_t *ipq_get_packet(const unsigned char *" buf ");"

.br

.BI "int ipq_get_msgerr(const unsigned char *" buf ");"

.SH DESCRIPTION

The

.B ipq_message_type

function returns the type of queue message returned to userspace

via

.BR ipq_read .

.PP

.B ipq_message_type

should always be called following a successful call to

.B ipq_read

to determine whether the message is a packet message or an

error message. The

.I buf

parameter should be the same data obtained from

the previous call to

.BR ipq_read .

.PP

.B ipq_message_type

will return one of the following values:

.TP

.B NLMSG_ERROR

An error message generated by the Netlink transport.

.PP

.TP

.B IPQM_PACKET

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

.PP

The

.B ipq_get_packet

function should be called if

.B ipq_message_type

returns

.BR IPQM_PACKET .

The

.I buf

parameter should point to the same data used for the call to

.BR ipq_message_type .

The pointer returned by

.B ipq_get_packet

points to a packet message, which is declared as follows:

.PP

.RS

.nf

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;

.fi

.RE

.PP

Each of these fields may be read by the application.  If the queue mode

is

.B IPQ_COPY_PACKET

and the

.I data_len

value is greater than zero, the packet payload contents may be accessed

in the memory following the

.B ipq_packet_msg_t

structure to a range of

.I data_len.

.PP

The

.I packet_id

field contains a packet identifier to be used when calling

.BR ipq_set_verdict .

.PP

The

.B ipq_get_msgerr

function should be called if

.B ipq_message_type

returns

.BR NLMSG_ERROR.

The

.I buf

parameter should point to the same data used for the call to

.BR ipq_message_type .

The value returned by

.B ipq_get_msgerr

is set by higher level kernel code and corresponds to standard

.B errno

values.

.SH BUGS

None known.

.SH AUTHOR

James Morris <jmorris@intercode.com.au>

.SH COPYRIGHT

Copyright (c) 2000-2001 Netfilter Core Team.

.PP

Distributed under the GNU General Public License.

.SH SEE ALSO

.BR iptables (8),

.BR libipq (3).