svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
pfil(9)
PFIL(9) BSD Kernel Developer's Manual PFIL(9)
NAME
pfil, pfil_head_register, pfil_head_unregister, pfil_head_get,
pfil_add_hook, pfil_add_hook_flags, pfil_remove_hook,
pfil_remove_hook_flags, pfil_run_hooks, pfil_rlock, pfil_runlock,
pfil_wlock, pfil_wunlock — 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 *, int dir, struct inpcb);
typedef int (*pfil_func_flags_t)(void *arg, struct mbuf **mp, struct ifnet *, int dir, int flags, struct inpcb);
int
pfil_head_register(struct pfil_head *head);
int
pfil_head_unregister(struct pfil_head *head);
struct pfil_head *
pfil_head_get(int af, u_long dlt);
int
pfil_add_hook(pfil_func_t, void *arg, struct pfil_head *);
int
pfil_add_hook_flags(pfil_func_flags_t, void *arg, int flags, struct pfil_head *);
int
pfil_remove_hook(pfil_func_t, void *arg, struct pfil_head *);
int
pfil_remove_hook_flags(pfil_func_flags_t, void *arg, int flags, struct pfil_head *);
int
pfil_run_hooks(struct pfil_head *head, struct mbuf **mp, struct ifnet *, int dir, int flags, struct inpcb *);
void
pfil_rlock(struct pfil_head *, struct rm_priotracker *);
void
pfil_runlock(struct pfil_head *, struct rm_priotracker *);
void
pfil_wlock(struct pfil_head *);
void
pfil_wunlock(struct pfil_head *);
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 trans‐
formations.
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. Each filtering point uses common per-VNET rmlock by
default. This can be changed by specifying PFIL_FLAG_PRIVATE_LOCK as
flags field in the pfil_head structure. Note that specifying private
lock can break filters sharing the same ruleset and/or state between dif‐
ferent data link types. 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 flags argument will indicate if an outgoing
packet is simply being forwarded with the value PFIL_FWD. 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 responsi‐
bility of the filter to free the packet.
Every filter hook is called with pfil 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 improve performance. Since pfil uses
rmlock(9) pfil_rlock() and pfil_runlock() require struct rm_priotracker
to be passed as argument. Filter can acquire and release writer lock via
pfil_wlock() and pfil_wunlock() functions. See rmlock(9) for more
details.
FILTERING POINTS
Currently, filtering points are implemented for the following link types:
AF_INET IPv4 packets.
AF_INET6 IPv6 packets.
AF_LINK Link-layer packets.
RETURN VALUES
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!
SEE ALSO
bpf(4), if_bridge(4), rmlock(9)
HISTORY
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. pfil lock export was
added in FreeBSD 10.0.
BUGS
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
this.
BSD March 10, 2018 BSD