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       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
       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,
       SIOCIPFFB  is  not  available  and  FIONREAD  will  return  but  not do

       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)