ipq_set_mode3

Usage

Overview

The 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.

The h parameter is a context handle which must previously have been returned successfully from a call to ipq_create_handle.

The mode parameter must be one of:

The range parameter is used to specify how many bytes of the payload to copy to userspace. It is only valid for IPQ_COPY_PACKET mode and is otherwise ignored. The maximum useful value for range is 65535 (greater values will be clamped to this by ip_queue).

ipq_set_mode is usually used immediately following ipq_create_handle to enable the flow of packets to userspace.

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.

Return value

On failure, -1 is returned.
On success, a non-zero positive value is returned.

Errors

On failure, a descriptive error message will be available via the ipq_errstr function.

Diagnostics

A relatively common failure may occur if the ip_queue module is not loaded. In this case, the following code excerpt:

status = ipq_set_mode(h, IPQ_COPY_META, 0);
if (status < 0) {
	ipq_perror("myapp");
	ipq_destroy_handle(h);
	exit(1);
}

would generate the following output:

myapp: Failed to send netlink message: Connection refused