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

NAME
     pfil, pfil_head_register, pfil_head_unregister, pfil_head_get,
     pfil_hook_get, pfil_add_hook, pfil_remove_hook, pfil_run_hooks,
     pfil_add_ihook, pfil_remove_ihook, pfil_run_addrhooks, pfil_run_ifhooks -
     packet filter interface

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

     int
     pfil_head_register(struct pfil_head *ph);

     int
     pfil_head_unregister(struct pfil_head *ph);

     struct pfil_head *
     pfil_head_get(int af, u_long dlt);

     struct packet_filter_hook *
     pfil_hook_get(int dir, struct pfil_head *ph);

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

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

     int
     (*func)(void *arg, struct mbuf **mp, struct ifnet *, int dir);

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

     int
     pfil_add_ihook(void (*ifunc)(), void *arg, int flags,
         struct pfil_head *ph);

     int
     pfil_remove_ihook(void (*ifunc)(), void *arg, int flags,
         struct pfil_head *ph);

     void
     (*ifunc)(void *arg, unsigned long cmd, void *ptr);

     void
     pfil_run_addrhooks(struct pfil_head *ph, unsigned long,
         struct ifaddr *ifa);

     void
     pfil_run_ifhooks(struct pfil_head *ph, unsigned long, struct ifnet *ifp);

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_type 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 (either 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

     By the same token, event handlers register/unregister themselves with the
     pfil_add_ihook() and pfil_remove_ihook() functions, respectively.  The
     event handler is called with its specified argument, the event id (either
     PFIL_IFNET_ATTACH or PFIL_IFNET_DETACH, see also below) or ioctl number,
     and the pointer to the network interface or the pointer to the ifaddr.

     The flags parameter, used in the pfil_add_ihook() and pfil_remove_ihook()
     functions, indicates when the filter should be called.  The flags are:

           PFIL_IFADDR      call me on interface reconfig (cmd is ioctl #)
           PFIL_IFNET       call me on interface attach/detach (cmd is either
                            PFIL_IFNET_ATTACH or PFIL_IFNET_DETACH)

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.

     pfil_add_ihook() and pfil_remove_ihook() were added in NetBSD 8.0.

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.

BUGS
     The current pfil implementation will need changes to suit a threaded
     kernel model.

NetBSD 8.99.34                 January 17, 2018                 NetBSD 8.99.34