Provided by: libnetfilter-log-doc_1.0.2-3_all 
NAME
nflog_fd, nflog_callback_register, nflog_handle_packet, nflog_bind_group,
nflog_unbind_group, nflog_set_mode, nflog_set_timeout, nflog_set_qthresh,
nflog_set_nlbufsiz, nflog_set_flags - Group handling
SYNOPSIS
#include <stddef.h>
#include <libnetfilter_log/libnetfilter_log.h>
int nflog_fd (struct nflog_handle *h)
int nflog_callback_register (struct nflog_g_handle *gh, nflog_callback *cb, void *data)
int nflog_handle_packet (struct nflog_handle *h, char *buf, int len)
struct nflog_g_handle * nflog_bind_group (struct nflog_handle *h, uint16_t num)
int nflog_unbind_group (struct nflog_g_handle *gh)
int nflog_set_mode (struct nflog_g_handle *gh, uint8_t mode, uint32_t range)
int nflog_set_timeout (struct nflog_g_handle *gh, uint32_t timeout)
int nflog_set_qthresh (struct nflog_g_handle *gh, uint32_t qthresh)
int nflog_set_nlbufsiz (struct nflog_g_handle *gh, uint32_t nlbufsiz)
int nflog_set_flags (struct nflog_g_handle *gh, uint16_t flags)
Detailed Description
Once libnetfilter_log library has been initialised (See LibrarySetup), it is possible to
bind the program to a specific group. This can be done using nflog_bind_group().
The group can then be tuned via nflog_set_mode() among many others.
Here's a little code snippet that binds to the group 100:
printf("binding this socket to group 100\n");
gh = nflog_bind_group(h, 100);
if (!gh) {
fprintf(stderr, "no handle for group 100\n");
exit(1);
}
printf("setting copy_packet mode\n");
if (nflog_set_mode(gh, NFULNL_COPY_PACKET, 0xffff) < 0) {
fprintf(stderr, "can't set packet copy mode\n");
exit(1);
}
Next step is the handling of incoming packets which can be done via a loop:
fd = nflog_fd(h);
while ((rv = recv(fd, buf, sizeof(buf), 0)) && rv >= 0) {
printf("pkt received (len=%u)\n", rv);
nflog_handle_packet(h, buf, rv);
}
Data and information about the packet can be fetched by using message parsing functions.
See also:
LibrarySetup man page (man nflog_open)
Parsing man page (man nflog_get_gid)
Function Documentation
struct nflog_g_handle* nflog_bind_group (struct nflog_handle * h, uint16_t num)
nflog_bind_group - bind a new handle to a specific group number.
Parameters
h Netfilter log handle obtained via call to nflog_open()
num the number of the group to bind to
Returns
an nflog_g_handle for the newly created group or NULL on failure.
Errors
EBUSY This process has already binded to the group
EOPNOTSUPP Request rejected by kernel. Another process has already binded to the
group, or this process is not running as root
int nflog_callback_register (struct nflog_g_handle * gh, nflog_callback * cb, void * data)
nflog_callback_register - register function to process packets
Parameters
gh Netfilter log group handle obtained by call to nflog_bind_group()
cb callback function to call for each logged packet
data custom data to pass to the callback function
Returns
0
int nflog_fd (struct nflog_handle * h)
nflog_fd - get the file descriptor associated with the nflog handler
Parameters
h handler obtained via call to nflog_open()
Returns
a file descriptor for the netlink connection associated with the given log connection
handle. The file descriptor can then be used for receiving the logged packets for
processing.
int nflog_handle_packet (struct nflog_handle * h, char * buf, int len)
nflog_handle_packet - handle a packet received from the nflog subsystem
Parameters
h Netfilter log handle obtained via call to nflog_open()
buf nflog data received from the kernel
len length of packet data in buffer
Triggers an associated callback for each packet contained in buf. Data can be read from
the queue using nflog_fd() and recv(). See example code in the Detailed Description.
Returns
0 on success, -1 if either the callback returned -ve or buf contains corrupt data.
errno is not reliably set: caller should zeroise first if interested.
int nflog_set_flags (struct nflog_g_handle * gh, uint16_t flags)
nflog_set_flags - set the nflog flags for this group
Parameters
gh Netfilter log group handle obtained by call to nflog_bind_group().
flags Flags that you want to set
There are two existing flags:
- NFULNL_CFG_F_SEQ: This enables local nflog sequence numbering.
- NFULNL_CFG_F_SEQ_GLOBAL: This enables global nflog sequence numbering.
- NFULNL_CFG_F_CONNTRACK: This enables to acquire related conntrack.
Returns
0 on success, -1 on failure with errno set.
Errors
from underlying calls, in exceptional circumstances
int nflog_set_mode (struct nflog_g_handle * gh, uint8_t mode, uint32_t range)
nflog_set_mode - set the amount of packet data that nflog copies to userspace
Parameters
gh Netfilter log group handle obtained by call to nflog_bind_group().
mode the part of the packet that we are interested in
range size of the packet that we want to get
Sets the amount of data to be copied to userspace for each packet logged to the given
group.
• NFULNL_COPY_NONE - do not copy any data
• NFULNL_COPY_META - copy only packet metadata
• NFULNL_COPY_PACKET - copy entire packet
Returns
0 on success, -1 on failure with errno set.
Errors
from underlying calls, in exceptional circumstances
int nflog_set_nlbufsiz (struct nflog_g_handle * gh, uint32_t nlbufsiz)
nflog_set_nlbufsiz - set the size of the nflog buffer for this group
Parameters
gh Netfilter log group handle obtained by call to nflog_bind_group().
nlbufsiz Size of the nflog buffer
This function sets the size (in bytes) of the buffer that is used to stack log messages in
nflog.
Warning
The use of this function is strongly discouraged. The default buffer size (which is
one memory page) provides the optimum results in terms of performance. Do not use this
function in your applications.
Returns
0 on success, -1 on failure with errno set.
Errors
from underlying calls, in exceptional circumstances
int nflog_set_qthresh (struct nflog_g_handle * gh, uint32_t qthresh)
nflog_set_qthresh - set the maximum amount of logs in buffer for this group
Parameters
gh Netfilter log group handle obtained by call to nflog_bind_group().
qthresh Maximum number of log entries
This function determines the maximum number of log entries in the buffer until it is
pushed to userspace.
Returns
0 on success, -1 on failure with errno set.
Errors
from underlying calls, in exceptional circumstances
int nflog_set_timeout (struct nflog_g_handle * gh, uint32_t timeout)
nflog_set_timeout - set the maximum time to push log buffer for this group
Parameters
gh Netfilter log group handle obtained by call to nflog_bind_group().
timeout Time to wait until the log buffer is pushed to userspace
This function allows one to set the maximum time that nflog waits until it pushes the log
buffer to userspace if no new logged packets have occured. Basically, nflog implements a
buffer to reduce the computational cost of delivering the log message to userspace.
Returns
0 on success, -1 on failure with errno set.
Errors
from underlying calls, in exceptional circumstances
int nflog_unbind_group (struct nflog_g_handle * gh)
nflog_unbind_group - unbind a group handle.
Parameters
gh Netfilter log group handle obtained via nflog_bind_group()
Returns
0 on success, -1 on failure with errno set.
Errors
from underlying calls, in exceptional circumstances
Author
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