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IPL(4)								       IPL(4)

  ipl -	IP packet log device

  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];
	  u_int	  fl_unit;
	  u_char  fl_ifname[4];
	  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	par-
  tial log records is not supported.

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


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