ipq_read (3) - Linux Man Pages

ipq_read: read queue messages from ip_queue and read into supplied buffer


ipq_read --- read queue messages from ip_queue and read into supplied buffer


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

ssize_t ipq_read(const struct ipq_handle *h, unsigned char *buf, size_t len, int timeout);


The ipq_read function reads a queue message from the kernel and copies it to the memory pointed to by buf to a maximum length of len.

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

The caller is responsible for ensuring that the memory pointed to by buf is large enough to contain len bytes.

The timeout parameter may be used to set a timeout for the operation, specified in microseconds. This is implemented internally by the library via the select system call. A value of zero provides normal, backwards-compatible blocking behaviour with no timeout. A negative value causes the function to return immediately.

Data returned via buf should not be accessed directly. Use the ipq_message_type, ipq_get_packet, and ipq_get_msgerr functions to access the queue message in the buffer.


On failure, -1 is returned.
On success, a non-zero positive value is returned when no timeout value is specified.
On success with a timeout value specified, zero is returned if no data was available to read, or if a non-blocked signal was caught. In the latter case, the global errno value will be set to EINTR.


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


While the ipq_read function may return successfully, the queue message copied to the buffer may itself be an error message from a higher level kernel component. Use ipq_message_type to determine if it is an error message, and ipq_get_msgerr to access the value of the message.


None known.


James Morris <jmorris [at] intercode.com.au>


Copyright (c) 2000-2001 Netfilter Core Team.

Distributed under the GNU General Public License.


Joost Remijn implemented the timeout feature, which appeared in the 1.2.4 release of iptables.


iptables(8), libipq(3), select(2).