pfil_hook_get man page on FreeBSD

Man page or keyword search:  
man Server   9747 pages
apropos Keyword Search (all sections)
Output format
FreeBSD logo
[printable version]

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

     pfil, pfil_head_register, pfil_head_unregister, pfil_head_get,
     pfil_hook_get, pfil_add_hook, pfil_remove_hook, pfil_run_hooks — packet
     filter interface

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

     pfil_head_register(struct pfil_head *head);

     pfil_head_unregister(struct pfil_head *head);

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

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

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

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

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

     pfil_run_hooks(struct pfil_head *head, struct mbuf **mp, struct ifnet *,
	 int dir, struct inpcb *);

     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 trans‐

     Packet filtering points are registered with pfil_head_register().	Fil‐
     tering 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 fil‐
     ter 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) that
     the packet is traveling.  The filter may change which mbuf the mbuf **
     argument references.  The filter returns an error (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.

     If successful, pfil_head_get() returns the pfil_head structure for the
     given key/dlt.  The pfil_add_hook() and pfil_remove_hook() functions
     return 0 if successful.  If called with flag PFIL_WAITOK,
     pfil_remove_hook() is expected to always succeed.

     The pfil_head_unregister() function might sleep!

     bpf(4), if_bridge(4)

     The pfil interface first appeared in NetBSD 1.3.  The pfil input and out‐
     put 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 fil‐
     tering 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.

     Fine-grained locking was added in FreeBSD 5.2.

     The pfil_hook_get() function is only safe for internal use.

     FreeBSD implements only hooks for AF_INET and AF_INET6.  Packets diverted
     through these hooks have data in host byte order contrary to the above

     The if_bridge(4) diverts AF_INET and AF_INET6 traffic according to its
     sysctl settings, but contrary to the above statements, the data is pro‐
     vided in host byte order.

     When a pfil_head is being modified, no traffic is diverted (to avoid
     deadlock).	 This means that traffic may be dropped unconditionally for a
     short period of time.  pfil_run_hooks() will return ENOBUFS to indicate

BSD			      September 29, 2004			   BSD

List of man pages available for FreeBSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net