NAME¶

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

SYNOPSIS¶

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

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

DESCRIPTION¶

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.

RETURN VALUE¶

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.

ERRORS¶

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

DIAGNOSTICS¶

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.

BUGS¶

None known.

AUTHOR¶

James Morris <jmorris@intercode.com.au>

COPYRIGHT¶

Copyright (c) 2000-2001 Netfilter Core Team.

Distributed under the GNU General Public License.

CREDITS¶

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

SEE ALSO¶

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