ipl(4)

NAME

ipl - IP packet log device

DESCRIPTION

The ipl pseudo device's purpose is to provide an easy way
to gather packet headers of packets you wish to log. If a
packet header is to be logged, the entire header is logged
(including any IP options - TCP/UDP options are not
included when it calculates header size) or not at all.
The packet contents are also logged after the header. If
the log reader is busy or otherwise unable to read log
records, up to IPLLOGSIZE (8192 is the default) bytes of
data are stored.

Prepending every packet header logged is a structure containing information relevant to the packet following and
why it was logged. The structure's format is as follows:

/*

* Log structure. Each packet header logged is prepended

by one of these.
* Following this in the log records read from the device

will be an ipflog
* structure which is then followed by any packet data.
*/

typedef struct iplog {

u_long ipl_sec;
u_long ipl_usec;
u_int ipl_len;
u_int ipl_count;
size_t ipl_dsize;
struct iplog *ipl_next;

} iplog_t;

typedef struct ipflog {
#if (defined(NetBSD) && (NetBSD <= 1991011) && (NetBSD >=

199603))

u_char fl_ifname[IFNAMSIZ];

#else

u_int fl_unit;
u_char fl_ifname[4];

#endif

u_char fl_plen; /* extra data after hlen

*/
u_char fl_hlen; /* length of IP headers

saved */
u_short fl_rule; /* assume never more than

64k rules, total */
u_32_t fl_flags;

} ipflog_t;

When reading from the ipl device, it is necessary to call
read(2) with a buffer big enough to hold at least 1 complete log record - reading of partial log records is not
supported.

If the packet contents are more than 128 bytes when log
body is used, then only 128 bytes of the packet contents
are logged.

Although it is only possible to read from the ipl device,
opening it for writing is required when using an ioctl
which changes any kernel data.

The ioctls which are loaded with this device can be found
under ipf(4). The ioctls which are for use with logging and don't affect the filter are:

ioctl(fd, SIOCIPFFB, int *)
ioctl(fd, FIONREAD, int *)

The SIOCIPFFB ioctl flushes the log buffer and returns the
number of bytes flushed. FIONREAD returns the number of
bytes currently used for storing log data. If IPFILTER_LOG is not defined when compiling, SIOCIPFFB is not
available and FIONREAD will return but not do anything.

There is currently no support for non-blocking IO with
this device, meaning all read operations should be considered blocking in nature (if there is no data to read, it
will sleep until some is made available).

SEE ALSO

ipf(4)

BUGS

Packet headers are dropped when the internal buffer
(static size) fills.

FILES

/dev/ipl0

IPL(4)