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PF(4) Device Drivers Manual PF(4)

pf — packet filter

pseudo-device pf

Packet filtering takes place in the kernel. A pseudo-device, /dev/pf, allows userland processes to control the behavior of the packet filter through an ioctl(2) interface. There are commands to enable and disable the filter, load rulesets, add and remove individual rules or state table entries, and retrieve statistics. The most commonly used functions are covered by pfctl(8).

Manipulations like loading a ruleset that involve more than a single ioctl(2) call require a so-called , which prevents the occurrence of multiple concurrent manipulations.

Fields of ioctl(2) parameter structures that refer to packet data (like addresses and ports) are generally expected in network byte-order.

Rules and address tables are contained in so-called . When servicing an ioctl(2) request, if the anchor field of the argument structure is empty, the kernel will use the default anchor (i.e., the main ruleset) in operations. Anchors are specified by name and may be nested, with components separated by ‘/’ characters, similar to how file system hierarchies are laid out. The final component of the anchor path is the anchor under which operations will be performed. Anchor names with characters after the terminating null byte are considered invalid; if used in an ioctl, EINVAL will be returned.

pf supports the following ioctl(2) commands, available through ⟨net/pfvar.h⟩:

Start the packet filter.
Stop the packet filter.
Start the ALTQ bandwidth control system (see altq(9)).
Stop the ALTQ bandwidth control system.
struct pfioc_rule *pr
struct pfioc_rule {
	u_int32_t	action;
	u_int32_t	ticket;
	u_int32_t	nr;
	char		anchor[MAXPATHLEN];
	char		anchor_call[MAXPATHLEN];
	struct pf_rule	rule;
};

Add rule at the end of the inactive ruleset. This call requires a ticket obtained through a preceding DIOCXBEGIN call. The optional anchor name indicates the anchor in which to append the rule. nr and action are ignored.

struct pfioc_altq *pa
Add an ALTQ discipline or queue. 
struct pfioc_altq {
	u_int32_t	action;
	u_int32_t	ticket;
	u_int32_t	nr;
	struct pf_altq  altq;
};
struct pfioc_rule *pr
Get a ticket for subsequent DIOCGETRULE calls and the number nr of rules in the active ruleset.
struct pfioc_rule *pr
Get a rule by its number nr using the ticket obtained through a preceding DIOCGETRULES call. If action is set to PF_GET_CLR_CNTR, the per-rule statistics on the requested rule are cleared.
struct pfioc_altq *pa
Get a ticket for subsequent DIOCGETALTQ calls and the number nr of queues in the active list.
struct pfioc_altq *pa
Get the queueing discipline altq by its number nr using the ticket obtained through a preceding DIOCGETALTQS call.
struct pfioc_qstats *pq
Get the statistics on a queue. 
struct pfioc_qstats {
	u_int32_t	 ticket;
	u_int32_t	 nr;
	void		*buf;
	int		 nbytes;
	u_int8_t	 scheduler;
};

This call fills in a pointer to the buffer of statistics buf, of length nbytes, for the queue specified by nr.

struct pfioc_ruleset *pr
struct pfioc_ruleset {
	u_int32_t	 nr;
	char		 path[MAXPATHLEN];
	char		 name[PF_ANCHOR_NAME_SIZE];
};

Get the number nr of rulesets (i.e., anchors) directly attached to the anchor named by path for use in subsequent DIOCGETRULESET calls. Nested anchors, since they are not directly attached to the given anchor, will not be included. This ioctl returns EINVAL if the given anchor does not exist.

struct pfioc_ruleset *pr
Get a ruleset (i.e., an anchor) name by its number nr from the given anchor path, the maximum number of which can be obtained from a preceding DIOCGETRULESETS call. This ioctl returns EINVAL if the given anchor does not exist or EBUSY if another process is concurrently updating a ruleset.
struct pfioc_state *ps
Add a state entry. 
struct pfioc_state {
	struct pfsync_state	state;
};
struct pfioc_state *ps
Extract the entry identified by the id and creatorid fields of the state structure from the state table.
struct pfioc_state_kill *psk
Remove matching entries from the state table. This ioctl returns the number of killed states in psk_killed. 
struct pfioc_state_kill {
	struct pf_state_cmp	psk_pfcmp;
	sa_family_t		psk_af;
	int			psk_proto;
	struct pf_rule_addr	psk_src;
	struct pf_rule_addr	psk_dst;
	char			psk_ifname[IFNAMSIZ];
	char			psk_label[PF_RULE_LABEL_SIZE];
	u_int			psk_killed;
	u_int16_t		psk_rdomain;
};
struct pfioc_state_kill *psk
Clear all states. It works like DIOCKILLSTATES, but ignores all fields of the pfioc_state_kill structure, except psk_ifname.
struct pf_status *s
Get the internal packet filter statistics. 
struct pf_status {
	u_int64_t	counters[PFRES_MAX];
	u_int64_t	lcounters[LCNT_MAX];	/* limit counters */
	u_int64_t	fcounters[FCNT_MAX];
	u_int64_t	scounters[SCNT_MAX];
	u_int64_t	pcounters[2][2][3];
	u_int64_t	bcounters[2][2];
	u_int64_t	stateid;
	time_t		since;
	u_int32_t	running;
	u_int32_t	states;
	u_int32_t	src_nodes;
	u_int32_t	debug;
	u_int32_t	hostid;
	u_int32_t	reass;			/* reassembly */
	char		ifname[IFNAMSIZ];
	u_int8_t	pf_chksum[MD5_DIGEST_LENGTH];
};
Clear the internal packet filter statistics.
struct pfioc_natlook *pnl
Look up a state table entry by source and destination addresses and ports. 
struct pfioc_natlook {
	struct pf_addr	 saddr;
	struct pf_addr	 daddr;
	struct pf_addr	 rsaddr;
	struct pf_addr	 rdaddr;
	u_int16_t	 rdomain;
	u_int16_t	 rrdomain;
	u_int16_t	 sport;
	u_int16_t	 dport;
	u_int16_t	 rsport;
	u_int16_t	 rdport;
	sa_family_t	 af;
	u_int8_t	 proto;
	u_int8_t	 direction;
};

This was primarily used to support transparent proxies with rdr-to rules. New proxies should use divert-to rules instead. These do not require access to the privileged /dev/pf device and preserve the original destination address for getsockname(2). For SOCK_DGRAM sockets, the ip(4) socket options IP_RECVDSTADDR and IP_RECVDSTPORT can be used to retrieve the destination address and port.

u_int32_t *level
Set the debug level. See the syslog(3) man page for a list of valid debug levels.
struct pfioc_states *ps
Get state table entries. 
struct pfioc_states {
	int	ps_len;
	union {
		caddr_t		     psu_buf;
		struct pfsync_state *psu_states;
	} ps_u;
#define ps_buf		ps_u.psu_buf
#define ps_states	ps_u.psu_states
};

If ps_len is non-zero on entry, as many states as possible that can fit into this size will be copied into the supplied buffer ps_states. On exit, ps_len is always set to the total size required to hold all state table entries (i.e., it is set to sizeof(struct pfsync_state) * nr).

struct pfioc_rule *pcr
Add or remove the rule in the ruleset specified by rule.action.

The type of operation to be performed is indicated by action, which can be any of the following:

enum	{ PF_CHANGE_NONE, PF_CHANGE_ADD_HEAD, PF_CHANGE_ADD_TAIL,
	  PF_CHANGE_ADD_BEFORE, PF_CHANGE_ADD_AFTER,
	  PF_CHANGE_REMOVE, PF_CHANGE_GET_TICKET };

ticket must be set to the value obtained with PF_CHANGE_GET_TICKET for all actions except PF_CHANGE_GET_TICKET. anchor indicates to which anchor the operation applies. nr indicates the rule number against which PF_CHANGE_ADD_BEFORE, PF_CHANGE_ADD_AFTER, or PF_CHANGE_REMOVE actions are applied.

struct pfioc_tm *pt
struct pfioc_tm {
	int		 timeout;
	int		 seconds;
};

Set the state timeout of timeout to seconds. The old value will be placed into seconds. For possible values of timeout, consult the PFTM_* values in ⟨net/pfvar.h⟩.

struct pfioc_tm *pt
Get the state timeout of timeout. The value will be placed into the seconds field.
Clear per-rule statistics.
struct pfioc_limit *pl
Set the hard limits on the memory pools used by the packet filter. 
struct pfioc_limit {
	int		index;
	unsigned	limit;
};

enum	{ PF_LIMIT_STATES, PF_LIMIT_SRC_NODES, PF_LIMIT_FRAGS,
	  PF_LIMIT_TABLES, PF_LIMIT_TABLE_ENTRIES, PF_LIMIT_MAX };
struct pfioc_limit *pl
Get the hard limit for the memory pool indicated by index.
struct pfioc_table *io
Clear all tables. All the ioctls that manipulate radix tables use the same structure described below. For DIOCRCLRTABLES, pfrio_ndel contains on exit the number of tables deleted. 
struct pfioc_table {
	struct pfr_table	 pfrio_table;
	void			*pfrio_buffer;
	int			 pfrio_esize;
	int			 pfrio_size;
	int			 pfrio_size2;
	int			 pfrio_nadd;
	int			 pfrio_ndel;
	int			 pfrio_nchange;
	int			 pfrio_flags;
	u_int32_t		 pfrio_ticket;
};
#define pfrio_exists    pfrio_nadd
#define pfrio_nzero     pfrio_nadd
#define pfrio_nmatch    pfrio_nadd
#define pfrio_naddr     pfrio_size2
#define pfrio_setflag   pfrio_size2
#define pfrio_clrflag   pfrio_nadd
struct pfioc_table *io
Create one or more tables. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. On exit, pfrio_nadd contains the number of tables effectively created. 
struct pfr_table {
	char		pfrt_anchor[MAXPATHLEN];
	char		pfrt_name[PF_TABLE_NAME_SIZE];
	u_int32_t	pfrt_flags;
	u_int8_t	pfrt_fback;
};
struct pfioc_table *io
Delete one or more tables. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. On exit, pfrio_ndel contains the number of tables effectively deleted.
struct pfioc_table *io
Get the list of all tables. On entry, pfrio_buffer[pfrio_size] contains a valid writeable buffer for pfr_table structures. On exit, pfrio_size contains the number of tables written into the buffer. If the buffer is too small, the kernel does not store anything but just returns the required buffer size, without error.
struct pfioc_table *io
This call is like DIOCRGETTABLES but is used to get an array of pfr_tstats structures. 
struct pfr_tstats {
	struct pfr_table pfrts_t;
	u_int64_t	 pfrts_packets
			     [PFR_DIR_MAX][PFR_OP_TABLE_MAX];
	u_int64_t	 pfrts_bytes
			     [PFR_DIR_MAX][PFR_OP_TABLE_MAX];
	u_int64_t	 pfrts_match;
	u_int64_t	 pfrts_nomatch;
	time_t		 pfrts_tzero;
	int		 pfrts_cnt;
	int		 pfrts_refcnt[PFR_REFCNT_MAX];
};
#define pfrts_name	 pfrts_t.pfrt_name
#define pfrts_flags	 pfrts_t.pfrt_flags
struct pfioc_table *io
Clear the statistics of one or more tables. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. On exit, pfrio_nzero contains the number of tables effectively cleared.
struct pfioc_table *io
Clear all addresses in a table. On entry, pfrio_table contains the table to clear. On exit, pfrio_ndel contains the number of addresses removed.
struct pfioc_table *io
Add one or more addresses to a table. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements to add to the table. pfrio_esize must be the size of struct pfr_addr. On exit, pfrio_nadd contains the number of addresses effectively added. 
struct pfr_addr {
	union {
		struct in_addr	 _pfra_ip4addr;
		struct in6_addr	 _pfra_ip6addr;
	}		 pfra_u;
	char		 pfra_ifname[IFNAMSIZ];
	u_int32_t	 pfra_states;
	u_int16_t	 pfra_weight;
	u_int8_t	 pfra_af;
	u_int8_t	 pfra_net;
	u_int8_t	 pfra_not;
	u_int8_t	 pfra_fback;
	u_int8_t	 pfra_type;
	u_int8_t	 pad[7];
};
#define pfra_ip4addr    pfra_u._pfra_ip4addr
#define pfra_ip6addr    pfra_u._pfra_ip6addr
struct pfioc_table *io
Delete one or more addresses from a table. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements to delete from the table. pfrio_esize must be the size of struct pfr_addr. On exit, pfrio_ndel contains the number of addresses effectively deleted.
struct pfioc_table *io
Replace the content of a table by a new address list. This is the most complicated command, which uses all the structure members.

On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements which become the new contents of the table. pfrio_esize must be the size of struct pfr_addr. Additionally, if pfrio_size2 is non-zero, pfrio_buffer[pfrio_size..pfrio_size2] must be a writeable buffer, into which the kernel can copy the addresses that have been deleted during the replace operation. On exit, pfrio_ndel, pfrio_nadd, and pfrio_nchange contain the number of addresses deleted, added, and changed by the kernel. If pfrio_size2 was set on entry, pfrio_size2 will point to the size of the buffer used, exactly like DIOCRGETADDRS.

struct pfioc_table *io
Get all the addresses of a table. On entry, pfrio_table contains the table ID and pfrio_buffer[pfrio_size] contains a valid writeable buffer for pfr_addr structures. On exit, pfrio_size contains the number of addresses written into the buffer. If the buffer was too small, the kernel does not store anything but just returns the required buffer size, without returning an error.
struct pfioc_table *io
This call is like DIOCRGETADDRS but is used to get an array of pfr_astats structures. 
struct pfr_astats {
	struct pfr_addr	 pfras_a;
	u_int64_t	 pfras_packets
			     [PFR_DIR_MAX][PFR_OP_ADDR_MAX];
	u_int64_t	 pfras_bytes
			     [PFR_DIR_MAX][PFR_OP_ADDR_MAX];
	time_t		 pfras_tzero;
};
struct pfioc_table *io
Clear the statistics of one or more addresses. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements to be cleared from the table. pfrio_esize must be the size of struct pfr_addr. On exit, pfrio_nzero contains the number of addresses effectively cleared.
struct pfioc_table *io
Test if the given addresses match a table. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements, each of which will be tested for a match in the table. pfrio_esize must be the size of struct pfr_addr. On exit, the kernel updates the pfr_addr array by setting the pfra_fback member appropriately.
struct pfioc_table *io
Change the PFR_TFLAG_CONST or PFR_TFLAG_PERSIST flags of a table. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. pfrio_setflag must contain the flags to add, while pfrio_clrflag must contain the flags to remove. On exit, pfrio_nchange and pfrio_ndel contain the number of tables altered or deleted by the kernel. Yes, tables can be deleted if one removes the PFR_TFLAG_PERSIST flag of an unreferenced table.
struct pfioc_table *io
Defines a table in the inactive set. On entry, pfrio_table contains the table ID and pfrio_buffer[pfrio_size] contains an array of pfr_addr structures to put in the table. A valid ticket must also be supplied to pfrio_ticket. On exit, pfrio_nadd contains 0 if the table was already defined in the inactive list or 1 if a new table has been created. pfrio_naddr contains the number of addresses effectively put in the table.
struct pfioc_trans *io
struct pfioc_trans {
	int		 size;	/* number of elements */
	int		 esize;	/* size of each element in bytes */
	struct pfioc_trans_e {
		int		type;
		char		anchor[MAXPATHLEN];
		u_int32_t	ticket;
	}		*array;
};

Clear all the inactive rulesets specified in the pfioc_trans_e array. For each ruleset, a ticket is returned for subsequent "add rule" ioctls, as well as for the DIOCXCOMMIT and DIOCXROLLBACK calls.

Ruleset types, identified by type, include the following:

Filter rules.
ALTQ disciplines.
Address tables.
struct pfioc_trans *io
Atomically switch a vector of inactive rulesets to the active rulesets. This call is implemented as a standard two-phase commit, which will either fail for all rulesets or completely succeed. All tickets need to be valid. This ioctl returns EBUSY if another process is concurrently updating some of the same rulesets.
struct pfioc_trans *io
Clean up the kernel by undoing all changes that have taken place on the inactive rulesets since the last DIOCXBEGIN. DIOCXROLLBACK will silently ignore rulesets for which the ticket is invalid.
u_int32_t *hostid
Set the host ID, which is used by pfsync(4) to identify which host created state table entries.
Flush the passive OS fingerprint table.
struct pf_osfp_ioctl *io
struct pf_osfp_ioctl {
	struct pf_osfp_entry	fp_os;
	pf_tcpopts_t		fp_tcpopts;	/* packed TCP options */
	u_int16_t		fp_wsize;	/* TCP window size */
	u_int16_t		fp_psize;	/* ip->ip_len */
	u_int16_t		fp_mss;		/* TCP MSS */
	u_int16_t		fp_flags;
	u_int8_t		fp_optcnt;	/* TCP option count */
	u_int8_t		fp_wscale;	/* TCP window scaling */
	u_int8_t		fp_ttl;		/* IPv4 TTL */

	int			fp_getnum;	/* DIOCOSFPGET number */
};

struct pf_osfp_entry {
	SLIST_ENTRY(pf_osfp_entry) fp_entry;
	pf_osfp_t		fp_os;
	int			fp_enflags;
#define PF_OSFP_EXPANDED	0x001		/* expanded entry */
#define PF_OSFP_GENERIC		0x002		/* generic signature */
#define PF_OSFP_NODETAIL	0x004		/* no p0f details */
#define PF_OSFP_LEN	32
	char			fp_class_nm[PF_OSFP_LEN];
	char			fp_version_nm[PF_OSFP_LEN];
	char			fp_subtype_nm[PF_OSFP_LEN];
};

Add a passive OS fingerprint to the table. Set fp_os.fp_os to the packed fingerprint, fp_os.fp_class_nm to the name of the class (Linux, Windows, etc), fp_os.fp_version_nm to the name of the version (NT, 95, 98), and fp_os.fp_subtype_nm to the name of the subtype or patchlevel. The members fp_mss, fp_wsize, fp_psize, fp_ttl, fp_optcnt, and fp_wscale are set to the TCP MSS, the TCP window size, the IP length, the IP TTL, the number of TCP options, and the TCP window scaling constant of the TCP SYN packet, respectively.

The fp_flags member is filled according to the ⟨net/pfvar.h⟩ include file PF_OSFP_* defines. The fp_tcpopts member contains packed TCP options. Each option uses PF_OSFP_TCPOPT_BITS bits in the packed value. Options include any of PF_OSFP_TCPOPT_NOP, PF_OSFP_TCPOPT_SACK, PF_OSFP_TCPOPT_WSCALE, PF_OSFP_TCPOPT_MSS, or PF_OSFP_TCPOPT_TS.

The fp_getnum member is not used with this ioctl.

The structure's slack space must be zeroed for correct operation; memset(3) the whole structure to zero before filling and sending to the kernel.

struct pf_osfp_ioctl *io
Get the passive OS fingerprint number fp_getnum from the kernel's fingerprint list. The rest of the structure members will come back filled. Get the whole list by repeatedly incrementing the fp_getnum number until the ioctl returns EBUSY.
struct pfioc_src_nodes *psn
struct pfioc_src_nodes {
	int	psn_len;
	union {
		caddr_t		psu_buf;
		struct pf_src_node	*psu_src_nodes;
	} psn_u;
#define psn_buf		psn_u.psu_buf
#define psn_src_nodes	psn_u.psu_src_nodes
};

Get the list of source nodes kept by sticky addresses and source tracking. The ioctl must be called once with psn_len set to 0. If the ioctl returns without error, psn_len will be set to the size of the buffer required to hold all the pf_src_node structures held in the table. A buffer of this size should then be allocated, and a pointer to this buffer placed in psn_buf. The ioctl must then be called again to fill this buffer with the actual source node data. After that call, psn_len will be set to the length of the buffer actually used.

Clear the tree of source tracking nodes.
struct pfioc_iface *io
Get the list of interfaces and interface drivers known to pf. All the ioctls that manipulate interfaces use the same structure described below: 
struct pfioc_iface {
	char			 pfiio_name[IFNAMSIZ];
	void			*pfiio_buffer;
	int			 pfiio_esize;
	int			 pfiio_size;
	int			 pfiio_nzero;
	int			 pfiio_flags;
};

If not empty, pfiio_name can be used to restrict the search to a specific interface or driver. pfiio_buffer[pfiio_size] is the user-supplied buffer for returning the data. On entry, pfiio_size contains the number of pfi_kif entries that can fit into the buffer. The kernel will replace this value by the real number of entries it wants to return. pfiio_esize should be set to sizeof(struct pfi_kif).

The data is returned in the pfi_kif structure described below:

struct pfi_kif {
	char				 pfik_name[IFNAMSIZ];
	RB_ENTRY(pfi_kif)		 pfik_tree;
	u_int64_t			 pfik_packets[2][2][2];
	u_int64_t			 pfik_bytes[2][2][2];
	time_t				 pfik_tzero;
	int				 pfik_flags;
	int				 pfik_flags_new;
	void				*pfik_ah_cookie;
	struct ifnet			*pfik_ifp;
	struct ifg_group		*pfik_group;
	int				 pfik_states;
	int				 pfik_rules;
	int				 pfik_routes;
	TAILQ_HEAD(, pfi_dynaddr)	 pfik_dynaddrs;
};
struct pfioc_iface *pi
Specify the interface for which statistics are accumulated.
struct pfioc_iface *io
Set the user settable flags (described above) of the pf internal interface description. The filtering process is the same as for DIOCIGETIFACES. 
#define PFI_IFLAG_SKIP	0x0100	/* skip filtering on interface */
struct pfioc_iface *io
Works as DIOCSETIFFLAG above but clears the flags.
struct pfioc_src_node_kill *psnk
Explicitly remove source tracking nodes. 
struct pfioc_src_node_kill {
	sa_family_t		 psnk_af;
	struct pf_rule_addr	 psnk_src;
	struct pf_rule_addr	 psnk_dst;
	u_int			 psnk_killed;
};

/dev/pf
packet filtering device.

The following example demonstrates how to use the DIOCGETLIMIT command to show the hard limit of a memory pool used by the packet filter:

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>
#include <net/if.h>
#include <net/pfvar.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>

static const struct {
	const char	*name;
	int		index;
} pf_limits[] = {
	{ "states",		PF_LIMIT_STATES },
	{ "src-nodes",		PF_LIMIT_SRC_NODES },
	{ "frags",		PF_LIMIT_FRAGS },
	{ "tables",		PF_LIMIT_TABLES },
	{ "table-entries",	PF_LIMIT_TABLE_ENTRIES },
	{ NULL,			0 }
};

void
usage(void)
{
	extern char *__progname;
	int i;

	fprintf(stderr, "usage: %s [", __progname);
	for (i = 0; pf_limits[i].name; i++)
		fprintf(stderr, "%s%s", (i > 0 ? "|" : ""), pf_limits[i].name);
	fprintf(stderr, "]\n");
	exit(1);
}

int
main(int argc, char *argv[])
{
	struct pfioc_limit pl;
	int i, dev;
	int pool_index = -1;

	if (argc != 2)
		usage();

	for (i = 0; pf_limits[i].name; i++)
		if (!strcmp(argv[1], pf_limits[i].name)) {
			pool_index = pf_limits[i].index;
			break;
		}

	if (pool_index == -1) {
		warnx("no such memory pool: %s", argv[1]);
		usage();
	}

	dev = open("/dev/pf", O_RDWR);
	if (dev == -1)
		err(1, "open(\"/dev/pf\") failed");

	bzero(&pl, sizeof(struct pfioc_limit));
	pl.index = pool_index;

	if (ioctl(dev, DIOCGETLIMIT, &pl))
		err(1, "DIOCGETLIMIT");

	printf("The %s memory pool has ", pf_limits[i].name);
	if (pl.limit == UINT_MAX)
		printf("unlimited entries.\n");
	else
		printf("a hard limit of %u entries.\n", pl.limit);

	return (0);
}

ioctl(2), bridge(4), pflog(4), pflow(4), pfsync(4), pf.conf(5), pfctl(8), altq(9)

The pf packet filtering mechanism first appeared in OpenBSD 3.0.

July 4, 2013 OpenBSD-5.4