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PFIL(9)               DragonFly Kernel Developer's Manual              PFIL(9)


NAME

     pfil, pfil_head_register, pfil_head_unregister, pfil_head_get,
     pfil_add_hook, pfil_remove_hook, pfil_run_hooks - packet filter interface


SYNOPSIS

     #include <sys/param.h>
     #include <sys/mbuf.h>
     #include <net/if.h>
     #include <net/pfil.h>

     typedef int
     (*pfil_func_t)(void *arg, struct mbuf **mp, struct ifnet *ifp, int dir);

     int
     pfil_head_register(struct pfil_head *ph);

     int
     pfil_head_unregister(struct pfil_head *pfh);

     struct pfil_head *
     pfil_head_get(int type, u_long val);

     int
     pfil_add_hook(pfil_func_t func, void *arg, int flags,
         struct pfil_head *ph);

     int
     pfil_remove_hook(pfil_func_t func, void *arg, int flags,
         struct pfil_head *ph);

     int
     pfil_run_hooks(struct pfil_head *ph, struct mbuf **mp, struct ifnet *ifp,
         int dir);


DESCRIPTION

     The pfil framework allows for a specified function to be invoked for
     every incoming or outgoing packet for a particular network I/O stream.
     These hooks may be used to implement a firewall or perform packet
     transformations.

     Packet filtering points are registered with pfil_head_register().
     Filtering points are identified by a key (void *) and a data link type
     (int) in the pfil_head structure.  Packet filters use the key and data
     link type to look up the filtering point with which they register
     themselves.  The key is unique to the filtering point.  The data link
     type is a bpf(4) DLT constant indicating what kind of header is present
     on the packet at the filtering point.  Filtering points may be
     unregistered with the pfil_head_unregister() function.

     Packet filters register/unregister themselves with a filtering point with
     the pfil_add_hook() and pfil_remove_hook() functions, respectively.  The
     head is looked up using the pfil_head_get() function, which takes the key
     and data link type that the packet filter expects.  Filters may provide
     an argument to be passed to the filter when invoked on a packet.

     When a filter is invoked, the packet appears just as if it "came off the
     wire".  That is, all protocol fields are in network byte order.  The
     filter is called with its specified argument, the pointer to the pointer
     to the mbuf containing the packet, the pointer to the network interface
     that the packet is traversing, and the direction (PFIL_IN or PFIL_OUT,
     see also below) that the packet is traveling.  The filter may change
     which mbuf the mbuf ** argument references.  The filter returns an errno
     if the packet processing is to stop, or 0 if the processing is to
     continue.  If the packet processing is to stop, it is the responsibility
     of the filter to free the packet.

     The flags parameter, used in the pfil_add_hook() and pfil_remove_hook()
     functions, indicates when the filter should be called.  The flags are:
           PFIL_IN       call me on incoming packets
           PFIL_OUT      call me on outgoing packets
           PFIL_ALL      call me on all of the above


SEE ALSO

     bpf(4)


HISTORY

     The pfil interface first appeared in NetBSD 1.3.  The pfil input and
     output lists were originally implemented as <sys/queue.h> LIST
     structures; however this was changed in NetBSD 1.4 to TAILQ structures.
     This change was to allow the input and output filters to be processed in
     reverse order, to allow the same path to be taken, in or out of the
     kernel.

     The pfil interface was changed in 1.4T to accept a 3rd parameter to both
     pfil_add_hook() and pfil_remove_hook(), introducing the capability of
     per-protocol filtering.  This was done primarily in order to support
     filtering of IPv6.

     In 1.5K, the pfil framework was changed to work with an arbitrary number
     of filtering points, as well as be less IP-centric.

     The pfil interface was imported from NetBSD into DragonFly 1.0 and was
     reworked to suit a threaded kernel model in DragonFly 2.1.


AUTHORS

     The pfil interface was designed and implemented by Matthew R. Green, with
     help from Darren Reed, Jason R. Thorpe and Charles M. Hannum.  Darren
     Reed added support for IPv6 in addition to IPv4.  Jason R. Thorpe added
     support for multiple hooks and other clean up.

DragonFly 6.3-DEVELOPMENT      January 16, 2015      DragonFly 6.3-DEVELOPMENT

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