Manual Reference Pages - PFIL_ADD_HOOK (9)
- packet filter interface
typedef int (*pfil_func_t)(void *arg, struct mbuf **mp, struct ifnet *, int dir, struct inpcb);
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
pfil_add_hook pfil_func_t void *arg int flags struct pfil_head *
pfil_remove_hook pfil_func_t void *arg int flags struct pfil_head *
pfil_run_hooks struct pfil_head *head struct mbuf **mp struct ifnet * int dir struct inpcb *
pfil_rlock struct pfil_head * struct rm_priotracker *
pfil_runlock struct pfil_head * struct rm_priotracker *
pfil_wlock struct pfil_head *
pfil_wunlock struct pfil_head *
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
Packet filtering points are registered with
Filtering points are identified by a key
(Vt void *)
and a data link type
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
DLT constant indicating what kind of header is present on the packet
at the filtering point.
Each filtering point uses common per-VNET rmlock by default.
This can be changed by specifying
field in the
Note that specifying private lock can break filters sharing the same
ruleset and/or state between different data link types.
Filtering points may be unregistered with the
Packet filters register/unregister themselves with a filtering point
The head is looked up using the
function, which takes the key and data link type that the packet filter
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
containing the packet, the pointer to the network
interface that the packet is traversing, and the direction
that the packet is traveling.
The filter may change which mbuf the
.Vt mbuf **
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.
Every filter hook is called with
read lock held.
All heads uses the same lock within the same VNET instance.
Packet filter can use this lock instead of own locking model to
to be passed as argument.
Filter can acquire and release writer lock via
for more details.
Currently, filtering points are implemented for the following link types:
structure for the given key/dlt.
return 0 if successful.
If called with flag
is expected to always succeed.
interface first appeared in
.Nx 1.3 .
input and output lists were originally implemented as
however this was changed in
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.
interface was changed in 1.4T to accept a 3rd parameter to both
introducing the capability of per-protocol filtering.
This was done primarily in order to support filtering of IPv6.
In 1.5K, the
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
.Fx 5.2 .
lock export was added in
.Fx 10.0 .
is being modified, no traffic is diverted
(to avoid deadlock).
This means that traffic may be dropped unconditionally for a short period
to indicate this.
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