IPQ\_READ(3) Linux Programmer's Manual IPQ\_READ(3)

# [NAME](#NAME)

ipq\_read — read queue messages from ip\_queue and read into supplied buffer

# [SYNOPSIS](#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](#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](#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](#ERRORS)

On error, a descriptive error message will be available via the **ipq\_errstr** function.

# [DIAGNOSTICS](#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](#BUGS)

None known.

# [AUTHOR](#AUTHOR)

James Morris <jmorris@intercode.com.au>

# [COPYRIGHT](#COPYRIGHT)

Copyright (c) 2000-2001 Netfilter Core Team.

Distributed under the GNU General Public License.

# [CREDITS](#CREDITS)

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

# [SEE ALSO](#SEE_ALSO)

[**iptables**(8)](/man/os/iptables/iptables.8), [**libipq**(3)](/man/os/iptables/libipq.3), [**select**(2)](/man/os/iptables/select.2).

16 October 2001 Linux iptables 1.2

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Document: ipq_read(3) from iptables 1.8.13-r4 (Chainguard OS)
Source: https://git.netfilter.org/iptables/