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IPL(4)			   Kernel Interfaces Manual			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  IPLLOG-
       SIZE (8192 is the default) bytes	of data	are stored.

       Prepending  every packet	header logged is a structure containing	infor-
       mation 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
       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

       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

	       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,  SIO-
       CIPFFB 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)




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