libipq/ipq_set_mode.3

.TH IPQ_SET_MODE 3 "16 October 2001" "Linux iptables 1.2" "Linux Programmer's Manual" 
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.SH NAME
ipq_set_mode \(em set the ip_queue queuing mode
.SH SYNOPSIS
.B #include <linux/netfilter.h>
.br
.B #include <libipq.h>
.sp
.BI "int ipq_set_mode(const struct ipq_handle *" h ", u_int8_t " mode ", size_t " range );
.SH DESCRIPTION
The
.B ipq_set_mode
function sends a message to the kernel ip_queue module, specifying whether
packet metadata only, or packet payloads as well as metadata should be copied to
userspace.
.PP
The
.I h
parameter is a context handle which must previously have been returned 
successfully from a call to
.BR ipq_create_handle .
.PP
The
.I mode
parameter must be one of:
.TP
.B IPQ_COPY_META
Copy only packet metadata to userspace.
.TP
.B IPQ_COPY_PACKET
Copy packet metadata and packet payloads to userspace.
.PP
The
.I range
parameter is used to specify how many bytes of the payload to copy
to userspace.  It is only valid for
.B IPQ_COPY_PACKET
mode and is otherwise ignored.  The maximum useful value for
.I range
is 65535 (greater values will be clamped to this by ip_queue).
.PP
.B ipq_set_mode
is usually used immediately following
.B ipq_create_handle
to enable the flow of packets to userspace.
.PP
Note that as the underlying Netlink messaging transport is connectionless,
the ip_queue module does not know that a userspace application is ready to
communicate until it receives a message such as this.
.SH RETURN VALUE
On failure, \-1 is returned.
.br
On success, a non-zero positive value is returned.
.SH ERRORS
On failure, a descriptive error message will be available
via the
.B ipq_errstr
function.
.SH DIAGNOSTICS
A relatively common failure may occur if the ip_queue module is not loaded.
In this case, the following code excerpt:
.PP
.RS
.nf
status = ipq_set_mode(h, IPQ_COPY_META, 0);
if (status < 0) {
	ipq_perror("myapp");
	ipq_destroy_handle(h);
	exit(1);
}
.RE
.fi
.PP
would generate the following output:
.PP
.I myapp: Failed to send netlink message: Connection refused
.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 libipq (3),
.BR iptables (8).