[RFC PATCH v2 6/6] src: add events reporting

[Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>]

This patch adds a basic events reporting option to nft.

The syntax is:
 % nft monitor [added|deleted] [tables|chains|rules|sets] [xml|json]

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
---
 include/mnl.h     |    3 
 include/netlink.h |    8 +
 include/rule.h    |    3 
 src/evaluate.c    |    1 
 src/mnl.c         |   45 ++++-
 src/netlink.c     |  474 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/parser.y      |   75 ++++++++
 src/rule.c        |   26 +++
 src/scanner.l     |    5 +
 9 files changed, 621 insertions(+), 19 deletions(-)

diff --git a/include/mnl.h b/include/mnl.h
index f4de27d..ece7ee7 100644
--- a/include/mnl.h
+++ b/include/mnl.h
@@ -67,4 +67,7 @@ int mnl_nft_setelem_get(struct mnl_socket *nf_sock, struct nft_set *nls);
 
 struct nft_ruleset *mnl_nft_ruleset_dump(struct mnl_socket *nf_sock,
 					 uint32_t family);
+int mnl_nft_event_listener(struct mnl_socket *nf_sock,
+			   int (*cb)(const struct nlmsghdr *nlh, void *data),
+			   void *cb_data);
 #endif /* _NFTABLES_MNL_H_ */
diff --git a/include/netlink.h b/include/netlink.h
index 4e3f8aa..627b25c 100644
--- a/include/netlink.h
+++ b/include/netlink.h
@@ -142,4 +142,12 @@ extern int netlink_io_error(struct netlink_ctx *ctx,
 extern struct nft_ruleset *netlink_dump_ruleset(struct netlink_ctx *ctx,
 						const struct handle *h,
 						const struct location *loc);
+struct netlink_mon_handler {
+	uint32_t		selector;
+	uint32_t		format;
+	struct netlink_ctx	*ctx;
+	const struct location	*loc;
+};
+
+extern int netlink_monitor(struct netlink_mon_handler *monhandler);
 #endif /* NFTABLES_NETLINK_H */
diff --git a/include/rule.h b/include/rule.h
index 9791cea..52e2aaa 100644
--- a/include/rule.h
+++ b/include/rule.h
@@ -210,6 +210,7 @@ extern void set_print_plain(const struct set *s);
  * @CMD_FLUSH:		flush container
  * @CMD_RENAME:		rename object
  * @CMD_EXPORT:		export the ruleset in a given format
+ * @CMD_MONITOR:	event listener
  */
 enum cmd_ops {
 	CMD_INVALID,
@@ -221,6 +222,7 @@ enum cmd_ops {
 	CMD_FLUSH,
 	CMD_RENAME,
 	CMD_EXPORT,
+	CMD_MONITOR,
 };
 
 /**
@@ -276,6 +278,7 @@ struct cmd {
 	};
 	const void		*arg;
 	uint32_t		format;
+	uint32_t		mon_selector;
 };
 
 extern struct cmd *cmd_alloc(enum cmd_ops op, enum cmd_obj obj,
diff --git a/src/evaluate.c b/src/evaluate.c
index f10d0d9..914ea23 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1410,6 +1410,7 @@ int cmd_evaluate(struct eval_ctx *ctx, struct cmd *cmd)
 	case CMD_FLUSH:
 	case CMD_RENAME:
 	case CMD_EXPORT:
+	case CMD_MONITOR:
 		return 0;
 	default:
 		BUG("invalid command operation %u\n", cmd->op);
diff --git a/src/mnl.c b/src/mnl.c
index e825fb0..7e34b31 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -34,24 +34,16 @@ uint32_t mnl_seqnum_alloc(void)
 }
 
 static int
-mnl_talk(struct mnl_socket *nf_sock, const void *data, unsigned int len,
-	 int (*cb)(const struct nlmsghdr *nlh, void *data), void *cb_data)
+mnl_talk_recv(struct mnl_socket *nf_sock, int seqnum, uint32_t portid,
+	      int (*cb)(const struct nlmsghdr *nlh, void *data),
+	      void *cb_data)
 {
-	char buf[MNL_SOCKET_BUFFER_SIZE];
-	uint32_t portid = mnl_socket_get_portid(nf_sock);
 	int ret;
-
-#ifdef DEBUG
-	if (debug_level & DEBUG_MNL)
-		mnl_nlmsg_fprintf(stdout, data, len, sizeof(struct nfgenmsg));
-#endif
-
-	if (mnl_socket_sendto(nf_sock, data, len) < 0)
-		return -1;
+	char buf[MNL_SOCKET_BUFFER_SIZE];
 
 	ret = mnl_socket_recvfrom(nf_sock, buf, sizeof(buf));
 	while (ret > 0) {
-		ret = mnl_cb_run(buf, ret, seq, portid, cb, cb_data);
+		ret = mnl_cb_run(buf, ret, seqnum, portid, cb, cb_data);
 		if (ret <= 0)
 			goto out;
 
@@ -64,6 +56,23 @@ out:
 	return ret;
 }
 
+static int
+mnl_talk(struct mnl_socket *nf_sock, const void *data, unsigned int len,
+	 int (*cb)(const struct nlmsghdr *nlh, void *data), void *cb_data)
+{
+	uint32_t portid = mnl_socket_get_portid(nf_sock);
+
+#ifdef DEBUG
+	if (debug_level & DEBUG_MNL)
+		mnl_nlmsg_fprintf(stdout, data, len, sizeof(struct nfgenmsg));
+#endif
+
+	if (mnl_socket_sendto(nf_sock, data, len) < 0)
+		return -1;
+
+	return mnl_talk_recv(nf_sock, seq, portid, cb, cb_data);
+}
+
 /*
  * Batching
  */
@@ -805,3 +814,13 @@ out:
 	nft_ruleset_free(rs);
 	return NULL;
 }
+
+/*
+ * events
+ */
+int mnl_nft_event_listener(struct mnl_socket *nf_sock,
+			   int (*cb)(const struct nlmsghdr *nlh, void *data),
+			   void *cb_data)
+{
+	return mnl_talk_recv(nf_sock, 0, 0, cb, cb_data);
+}
diff --git a/src/netlink.c b/src/netlink.c
index 43af5d1..c7532eb 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -20,6 +20,7 @@
 #include <libnftnl/chain.h>
 #include <libnftnl/expr.h>
 #include <libnftnl/set.h>
+#include <linux/netfilter/nfnetlink.h>
 #include <linux/netfilter/nf_tables.h>
 #include <linux/netfilter.h>
 
@@ -32,6 +33,7 @@
 #include <erec.h>
 
 static struct mnl_socket *nf_sock;
+static struct mnl_socket *nf_mon_sock;
 
 const struct input_descriptor indesc_netlink = {
 	.name	= "netlink",
@@ -42,12 +44,18 @@ const struct location netlink_location = {
 	.indesc	= &indesc_netlink,
 };
 
-static void __init netlink_open_sock(void)
+static struct mnl_socket *nfsock_open(void)
 {
-	nf_sock = mnl_socket_open(NETLINK_NETFILTER);
-	if (nf_sock == NULL)
+	struct mnl_socket *s = mnl_socket_open(NETLINK_NETFILTER);
+	if (s == NULL)
 		memory_allocation_error();
 
+	return s;
+}
+
+static void __init netlink_open_sock(void)
+{
+	nf_sock = nfsock_open();
 	fcntl(mnl_socket_get_fd(nf_sock), F_SETFL, O_NONBLOCK);
 	mnl_batch_init();
 }
@@ -55,6 +63,13 @@ static void __init netlink_open_sock(void)
 static void __exit netlink_close_sock(void)
 {
 	mnl_socket_close(nf_sock);
+	if (nf_mon_sock)
+		mnl_socket_close(nf_mon_sock);
+}
+
+static void netlink_open_mon_sock(void)
+{
+	nf_mon_sock = nfsock_open();
 }
 
 int netlink_io_error(struct netlink_ctx *ctx, const struct location *loc,
@@ -1047,3 +1062,456 @@ struct nft_ruleset *netlink_dump_ruleset(struct netlink_ctx *ctx,
 
 	return rs;
 }
+
+static void netlink_events_printf_wrapper(const char *content,
+					  uint32_t format, int type)
+{
+	const char *type_str = "unknown";
+
+	switch (type) {
+	case NFT_MSG_NEWTABLE:
+	case NFT_MSG_NEWCHAIN:
+	case NFT_MSG_NEWSET:
+	case NFT_MSG_NEWRULE:
+		type_str = "add";
+		break;
+	case NFT_MSG_DELTABLE:
+	case NFT_MSG_DELCHAIN:
+	case NFT_MSG_DELSET:
+	case NFT_MSG_DELRULE:
+		type_str = "del";
+		break;
+	}
+
+	switch (format) {
+	case NFT_OUTPUT_XML:
+		printf("<event><type>%s</type>"
+		       "<nftables>%s</nftables></event>\n",
+		       type_str, content);
+		break;
+	case NFT_OUTPUT_JSON:
+		printf("{event:{type:\"%s\",{\"nftables\":[\"%s\"]}}}\n",
+		       type_str, content);
+		break;
+	default:
+		BUG("Unknown monitor output format.\n");
+	}
+}
+
+static int netlink_events_table_cb(const struct nlmsghdr *nlh, int type,
+				   struct netlink_mon_handler *monh)
+{
+	struct nft_table *nlt;
+	uint32_t family;
+	char buf[4096];
+
+	nlt = nft_table_alloc();
+	if (nlt == NULL)
+		memory_allocation_error();
+
+	if (nft_table_nlmsg_parse(nlh, nlt) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				"Could not parse table: %s",
+				strerror(errno));
+		goto err;
+	}
+
+	if (monh->format == NFT_OUTPUT_DEFAULT) {
+		if (type == NFT_MSG_NEWTABLE)
+			printf("add table ");
+		else
+			printf("delete table ");
+
+		family = nft_table_attr_get_u32(nlt, NFT_TABLE_ATTR_FAMILY);
+
+		printf("%s %s\n", family2str(family),
+		       nft_table_attr_get_str(nlt, NFT_TABLE_ATTR_NAME));
+	} else {
+		nft_table_snprintf(buf, sizeof(buf), nlt, monh->format, 0);
+		netlink_events_printf_wrapper(buf, monh->format, type);
+	}
+
+err:
+	nft_table_free(nlt);
+	return MNL_CB_OK;
+}
+
+static int netlink_events_chain_cb(const struct nlmsghdr *nlh, int type,
+				   struct netlink_mon_handler *monh)
+{
+	struct nft_chain *nlc;
+	struct chain *c;
+	uint32_t family;
+	char buf[4096];
+
+	nlc = nft_chain_alloc();
+	if (nlc == NULL)
+		memory_allocation_error();
+
+	if (nft_chain_nlmsg_parse(nlh, nlc) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				 "Could not parse chain: %s",
+				 strerror(errno));
+		goto out;
+	}
+
+	if (monh->format == NFT_OUTPUT_DEFAULT) {
+		if (type == NFT_MSG_NEWCHAIN) {
+			printf("add ");
+			c = netlink_delinearize_chain(monh->ctx, nlc);
+			chain_print_plain(c);
+			chain_free(c);
+		} else {
+			family = nft_chain_attr_get_u32(nlc,
+							NFT_CHAIN_ATTR_FAMILY);
+			printf("delete chain %s %s %s\n", family2str(family),
+			       nft_chain_attr_get_str(nlc,
+						      NFT_CHAIN_ATTR_TABLE),
+			       nft_chain_attr_get_str(nlc,
+						      NFT_CHAIN_ATTR_NAME));
+		}
+	} else {
+		nft_chain_snprintf(buf, sizeof(buf), nlc, monh->format, 0);
+		netlink_events_printf_wrapper(buf, monh->format, type);
+	}
+
+out:
+	nft_chain_free(nlc);
+	return MNL_CB_OK;
+}
+
+static int netlink_events_set_cb(const struct nlmsghdr *nlh, int type,
+				 struct netlink_mon_handler *monh)
+{
+	struct nft_set *nls;
+	struct set *set;
+	uint32_t family, flags;
+	char buf[4096];
+
+	nls = nft_set_alloc();
+	if (nls == NULL)
+		memory_allocation_error();
+
+	if (nft_set_nlmsg_parse(nlh, nls) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				 "Could not parse set: %s",
+				 strerror(errno));
+		goto out;
+	}
+
+	flags = nft_set_attr_get_u32(nls, NFT_SET_ATTR_FLAGS);
+	if (flags & SET_F_ANONYMOUS)
+		goto out;
+
+	if (monh->format == NFT_OUTPUT_DEFAULT) {
+		if (type == NFT_MSG_NEWSET) {
+			printf("add ");
+			set = netlink_delinearize_set(monh->ctx, nls);
+			set_print_plain(set);
+			set_free(set);
+		} else {
+			family = nft_set_attr_get_u32(nls,
+						      NFT_SET_ATTR_FAMILY);
+			printf("delete set %s %s %s",
+			       family2str(family),
+			       nft_set_attr_get_str(nls, NFT_SET_ATTR_TABLE),
+			       nft_set_attr_get_str(nls, NFT_SET_ATTR_NAME));
+		}
+
+		printf("\n");
+
+	} else {
+		nft_set_snprintf(buf, sizeof(buf), nls, monh->format, 0);
+		netlink_events_printf_wrapper(buf, monh->format, type);
+	}
+
+out:
+	nft_set_free(nls);
+	return MNL_CB_OK;
+}
+
+static int netlink_events_rule_cb(const struct nlmsghdr *nlh, int type,
+				  struct netlink_mon_handler *monh)
+{
+	struct nft_rule *nlr;
+	struct rule *r;
+	char buf[4096];
+	uint32_t fam;
+	const char *family;
+	const char *table;
+	const char *chain;
+	uint64_t handle;
+
+	nlr = nft_rule_alloc();
+	if (nlr == NULL)
+		memory_allocation_error();
+
+	if (nft_rule_nlmsg_parse(nlh, nlr) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				 "Could not parse rule: %s",
+				 strerror(errno));
+		goto out;
+	}
+
+	if (monh->format == NFT_OUTPUT_DEFAULT) {
+		fam = nft_rule_attr_get_u32(nlr, NFT_RULE_ATTR_FAMILY);
+		family = family2str(fam);
+		table = nft_rule_attr_get_str(nlr, NFT_RULE_ATTR_TABLE);
+		chain = nft_rule_attr_get_str(nlr, NFT_RULE_ATTR_CHAIN);
+		handle = nft_rule_attr_get_u64(nlr, NFT_RULE_ATTR_HANDLE);
+
+		if (type == NFT_MSG_NEWRULE) {
+			r = netlink_delinearize_rule(monh->ctx, nlr);
+			printf("add rule %s %s %s", family, table, chain);
+			rule_print(r);
+			rule_free(r);
+			goto out;
+		}
+
+		printf("delete rule %s %s %s handle %u\n",
+		       family, table, chain, (unsigned int)handle);
+	} else {
+		nft_rule_snprintf(buf, sizeof(buf), nlr, monh->format, 0);
+		netlink_events_printf_wrapper(buf, monh->format, type);
+	}
+
+out:
+	nft_rule_free(nlr);
+	return MNL_CB_OK;
+}
+
+static void netlink_events_cache_addtable(struct netlink_mon_handler *monh,
+					  const struct nlmsghdr *nlh)
+{
+	struct nft_table *nlt;
+	struct table *t;
+
+	nlt = nft_table_alloc();
+	if (nlt == NULL)
+		memory_allocation_error();
+
+	if (nft_table_nlmsg_parse(nlh, nlt) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				"Could not parse table: %s",
+				strerror(errno));
+		goto out;
+	}
+
+	t = netlink_delinearize_table(monh->ctx, nlt);
+	table_add_hash(t);
+
+out:
+	nft_table_free(nlt);
+}
+
+static void netlink_events_cache_deltable(struct netlink_mon_handler *monh,
+					  const struct nlmsghdr *nlh)
+{
+	struct nft_table *nlt;
+	struct table *t;
+	struct handle h;
+
+	nlt = nft_table_alloc();
+	if (nlt == NULL)
+		memory_allocation_error();
+
+	if (nft_table_nlmsg_parse(nlh, nlt) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				"Could not parse table: %s",
+				strerror(errno));
+		goto out;
+	}
+
+	h.family = nft_table_attr_get_u32(nlt, NFT_TABLE_ATTR_FAMILY);
+	h.table = nft_table_attr_get_str(nlt, NFT_TABLE_ATTR_NAME);
+
+	t = table_lookup(&h);
+	if (t == NULL)
+		goto out;
+
+	list_del(&t->list);
+	table_free(t);
+
+out:
+	nft_table_free(nlt);
+}
+
+static void netlink_events_cache_addset(struct netlink_mon_handler *monh,
+					const struct nlmsghdr *nlh)
+{
+	struct nft_set *nls;
+	struct netlink_ctx set_tmpctx;
+	LIST_HEAD(msgs);
+	struct table *t;
+	struct set *s;
+	uint32_t flags;
+
+	nls = nft_set_alloc();
+	if (nls == NULL)
+		memory_allocation_error();
+
+	if (nft_set_nlmsg_parse(nlh, nls) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				"Could not parse set: %s",
+				strerror(errno));
+		goto out;
+	}
+
+	flags = nft_set_attr_get_u32(nls, NFT_SET_ATTR_FLAGS);
+	if (!(flags & SET_F_ANONYMOUS))
+		goto out;
+
+	memset(&set_tmpctx, 0, sizeof(set_tmpctx));
+	init_list_head(&set_tmpctx.list);
+	init_list_head(&msgs);
+	set_tmpctx.msgs = &msgs;
+	s = netlink_delinearize_set(&set_tmpctx, nls);
+
+	/* XXXX */
+	sleep(1);
+
+	/* only way, by now, to know set_elems (no set_elem events) */
+	if (netlink_get_setelems(&set_tmpctx, &s->handle, monh->loc, s) < 0)
+		goto out;
+
+	set_print(s);
+
+	t = table_lookup(&s->handle);
+	if (t == NULL)
+		goto out;
+
+	set_add_hash(s, t);
+out:
+	nft_set_free(nls);
+}
+
+static void netlink_events_cache_delsets(struct netlink_mon_handler *monh,
+					 const struct nlmsghdr *nlh)
+{
+	struct nft_rule *nlr;
+	struct handle th;
+	struct nft_rule_expr_iter *nlrei;
+	struct nft_rule_expr *nlre;
+	const char *expr_name, *set_name;
+	struct table *t;
+	struct set *s;
+
+	nlr = nft_rule_alloc();
+	if (nlr == NULL)
+		memory_allocation_error();
+
+	if (nft_rule_nlmsg_parse(nlh, nlr) < 0) {
+		netlink_io_error(monh->ctx, monh->loc,
+				 "Could not parse rule: %s",
+				 strerror(errno));
+		goto out;
+	}
+
+	th.table = nft_rule_attr_get_str(nlr, NFT_RULE_ATTR_TABLE);
+	th.family = nft_rule_attr_get_u32(nlr, NFT_RULE_ATTR_FAMILY);
+	t = table_lookup(&th);
+	if (t == NULL)
+		goto out;
+
+
+	nlrei = nft_rule_expr_iter_create(nlr);
+	if (nlrei == NULL)
+		memory_allocation_error();
+
+	nlre = nft_rule_expr_iter_next(nlrei);
+	while (nlre != NULL) {
+		expr_name = nft_rule_expr_get_str(nlre,
+						  NFT_RULE_EXPR_ATTR_NAME);
+		if (strcmp(expr_name, "lookup") != 0)
+			goto next;
+
+		set_name = nft_rule_expr_get_str(nlre, NFT_EXPR_LOOKUP_SET);
+		s = set_lookup(t, set_name);
+		if (s == NULL)
+			goto next;
+
+		list_del(&s->list);
+		set_free(s);
+next:
+		nlre = nft_rule_expr_iter_next(nlrei);
+	}
+	nft_rule_expr_iter_destroy(nlrei);
+
+out:
+	nft_rule_free(nlr);
+}
+
+static void netlink_events_cache_update(struct netlink_mon_handler *monh,
+					const struct nlmsghdr *nlh, int type)
+{
+	/* cache only needed when monitoring new rules in def. output format */
+	if (!(monh->selector & (1 << NFT_MSG_NEWRULE)) &&
+	    (monh->format != NFT_OUTPUT_DEFAULT))
+		return;
+
+	switch (type) {
+	case NFT_MSG_NEWTABLE:
+		netlink_events_cache_addtable(monh, nlh);
+		break;
+	case NFT_MSG_DELTABLE:
+		netlink_events_cache_deltable(monh, nlh);
+		break;
+	case NFT_MSG_NEWSET:
+		netlink_events_cache_addset(monh, nlh);
+		break;
+	case NFT_MSG_DELRULE:
+		/* there are no notification for anon-set deletion */
+		netlink_events_cache_delsets(monh, nlh);
+		break;
+	}
+}
+
+static int netlink_events_cb(const struct nlmsghdr *nlh, void *data)
+{
+	int ret = MNL_CB_OK;
+	int type = nlh->nlmsg_type & 0xFF;
+	struct netlink_mon_handler *monh = (struct netlink_mon_handler *)data;
+
+	netlink_events_cache_update(monh, nlh, type);
+
+	if (!(monh->selector & (1 << type)))
+		return ret;
+
+	switch (type) {
+	case NFT_MSG_NEWTABLE:
+	case NFT_MSG_DELTABLE:
+		ret = netlink_events_table_cb(nlh, type, monh);
+		break;
+	case NFT_MSG_NEWCHAIN:
+	case NFT_MSG_DELCHAIN:
+		ret = netlink_events_chain_cb(nlh, type, monh);
+		break;
+	case NFT_MSG_NEWSET:
+	case NFT_MSG_DELSET:
+		ret = netlink_events_set_cb(nlh, type, monh);
+		break;
+	case NFT_MSG_NEWRULE:
+	case NFT_MSG_DELRULE:
+		ret = netlink_events_rule_cb(nlh, type, monh);
+		break;
+	default:
+		BUG("Unknow event received from kernel.\n");
+		break;
+	}
+
+	return ret;
+}
+
+int netlink_monitor(struct netlink_mon_handler *monhandler)
+{
+	netlink_open_mon_sock();
+
+	if (mnl_socket_bind(nf_mon_sock, (1 << (NFNLGRP_NFTABLES-1)),
+			    MNL_SOCKET_AUTOPID) < 0)
+		return netlink_io_error(monhandler->ctx, monhandler->loc,
+					"Could not bind to netlink socket %s",
+					strerror(errno));
+
+	return mnl_nft_event_listener(nf_mon_sock, netlink_events_cb,
+				      monhandler);
+}
diff --git a/src/parser.y b/src/parser.y
index b3acc74..a154696 100644
--- a/src/parser.y
+++ b/src/parser.y
@@ -163,12 +163,16 @@ static void location_update(struct location *loc, struct location *rhs, int n)
 %token TABLE			"table"
 %token TABLES			"tables"
 %token CHAIN			"chain"
+%token CHAINS			"chains"
 %token RULE			"rule"
+%token RULES			"rules"
 %token SETS			"sets"
 %token SET			"set"
 %token ELEMENT			"element"
 %token MAP			"map"
 %token HANDLE			"handle"
+%token ADDED			"added"
+%token DELETED			"deleted"
 
 %token INET			"inet"
 
@@ -181,6 +185,7 @@ static void location_update(struct location *loc, struct location *rhs, int n)
 %token RENAME			"rename"
 %token DESCRIBE			"describe"
 %token EXPORT			"export"
+%token MONITOR			"monitor"
 
 %token ACCEPT			"accept"
 %token DROP			"drop"
@@ -361,8 +366,8 @@ static void location_update(struct location *loc, struct location *rhs, int n)
 %type <cmd>			line
 %destructor { cmd_free($$); }	line
 
-%type <cmd>			base_cmd add_cmd create_cmd insert_cmd delete_cmd list_cmd flush_cmd rename_cmd export_cmd
-%destructor { cmd_free($$); }	base_cmd add_cmd create_cmd insert_cmd delete_cmd list_cmd flush_cmd rename_cmd export_cmd
+%type <cmd>			base_cmd add_cmd create_cmd insert_cmd delete_cmd list_cmd flush_cmd rename_cmd export_cmd monitor_cmd
+%destructor { cmd_free($$); }	base_cmd add_cmd create_cmd insert_cmd delete_cmd list_cmd flush_cmd rename_cmd export_cmd monitor_cmd
 
 %type <handle>			table_spec tables_spec chain_spec chain_identifier ruleid_spec
 %destructor { handle_free(&$$); } table_spec tables_spec chain_spec chain_identifier ruleid_spec
@@ -485,7 +490,7 @@ static void location_update(struct location *loc, struct location *rhs, int n)
 %destructor { expr_free($$); }	ct_expr
 %type <val>			ct_key
 
-%type <val>			export_format
+%type <val>			export_format	output_format	mon_selector
 
 %%
 
@@ -585,6 +590,7 @@ base_cmd		:	/* empty */	add_cmd		{ $$ = $1; }
 			|	FLUSH		flush_cmd	{ $$ = $2; }
 			|	RENAME		rename_cmd	{ $$ = $2; }
 			|	EXPORT		export_cmd	{ $$ = $2; }
+			|	MONITOR		monitor_cmd	{ $$ = $2; }
 			|	DESCRIBE	primary_expr
 			{
 				expr_describe($2);
@@ -752,6 +758,69 @@ export_cmd		:	export_format
 			}
 			;
 
+monitor_cmd		:	mon_selector	output_format
+			{
+				struct handle h = { .family = NFPROTO_UNSPEC };
+				$$ = cmd_alloc(CMD_MONITOR, CMD_OBJ_RULESET, &h, &@$, NULL);
+				$$->mon_selector = $1;
+				$$->format = $2;
+			}
+			;
+
+mon_selector		:	/* empty */
+			{
+				$$ |= (1 << NFT_MSG_NEWRULE);	$$ |= (1 << NFT_MSG_DELRULE);
+				$$ |= (1 << NFT_MSG_NEWSET);	$$ |= (1 << NFT_MSG_DELSET);
+				$$ |= (1 << NFT_MSG_NEWCHAIN);	$$ |= (1 << NFT_MSG_DELCHAIN);
+				$$ |= (1 << NFT_MSG_NEWTABLE);	$$ |= (1 << NFT_MSG_DELTABLE);
+			}
+			|	ADDED
+			{
+				$$ |= (1 << NFT_MSG_NEWRULE);
+				$$ |= (1 << NFT_MSG_NEWSET);
+				$$ |= (1 << NFT_MSG_NEWCHAIN);
+				$$ |= (1 << NFT_MSG_NEWTABLE);
+			}
+			|	DELETED
+			{
+				$$ |= (1 << NFT_MSG_DELRULE);
+				$$ |= (1 << NFT_MSG_DELSET);
+				$$ |= (1 << NFT_MSG_DELCHAIN);
+				$$ |= (1 << NFT_MSG_DELTABLE);
+			}
+			|	TABLES
+			{
+				$$ |= (1 << NFT_MSG_NEWTABLE);	$$ |= (1 << NFT_MSG_DELTABLE);
+			}
+			|	ADDED 	TABLES 	{	$$ |= (1 << NFT_MSG_NEWTABLE); }
+			|	DELETED	TABLES	{	$$ |= (1 << NFT_MSG_DELTABLE); }
+			|	CHAIN
+			{
+				$$ |= (1 << NFT_MSG_NEWCHAIN);	$$ |= (1 << NFT_MSG_DELCHAIN);
+			}
+			|	ADDED	CHAINS	{	$$ |= (1 << NFT_MSG_NEWCHAIN); }
+			|	DELETED	CHAINS	{	$$ |= (1 << NFT_MSG_DELCHAIN); }
+			|	SET
+			{
+				$$ |= (1 << NFT_MSG_NEWSET);	$$ |= (1 << NFT_MSG_DELSET);
+			}
+			|	ADDED	SETS	{	$$ |= (1 << NFT_MSG_NEWSET); }
+			|	DELETED SETS	{	$$ |= (1 << NFT_MSG_DELSET); }
+			|	RULE
+			{
+				$$ |= (1 << NFT_MSG_NEWRULE);	$$ |= (1 << NFT_MSG_DELRULE);
+			}
+			|	ADDED 	RULES	{	$$ |= (1 << NFT_MSG_NEWRULE); }
+			|	DELETED RULES	{	$$ |= (1 << NFT_MSG_DELRULE); }
+			;
+
+output_format		:	/* empty */
+			{
+				$$ = NFT_OUTPUT_DEFAULT;
+			}
+			|	export_format
+			;
+
 table_block_alloc	:	/* empty */
 			{
 				$$ = table_alloc();
diff --git a/src/rule.c b/src/rule.c
index d8a065a..72fc306 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -799,6 +799,30 @@ static int do_command_rename(struct netlink_ctx *ctx, struct cmd *cmd)
 	return 0;
 }
 
+static int do_command_monitor(struct netlink_ctx *ctx, struct cmd *cmd)
+{
+	struct table *t, *nt;
+	struct netlink_mon_handler monhandler;
+
+	/* cache only needed if monitoring new rules in def. output format */
+	if ((cmd->mon_selector & (1 << NFT_MSG_NEWRULE)) &&
+	    (cmd->format == NFT_OUTPUT_DEFAULT)) {
+		if (netlink_list_tables(ctx, &cmd->handle, &cmd->location) < 0)
+			return -1;
+
+		list_for_each_entry_safe(t, nt, &ctx->list, list) {
+			table_add_hash(t);
+		}
+	}
+
+	monhandler.selector = cmd->mon_selector;
+	monhandler.format = cmd->format;
+	monhandler.ctx = ctx;
+	monhandler.loc = &cmd->location;
+
+	return netlink_monitor(&monhandler);
+}
+
 int do_command(struct netlink_ctx *ctx, struct cmd *cmd)
 {
 	switch (cmd->op) {
@@ -818,6 +842,8 @@ int do_command(struct netlink_ctx *ctx, struct cmd *cmd)
 		return do_command_rename(ctx, cmd);
 	case CMD_EXPORT:
 		return do_command_export(ctx, cmd);
+	case CMD_MONITOR:
+		return do_command_monitor(ctx, cmd);
 	default:
 		BUG("invalid command object type %u\n", cmd->obj);
 	}
diff --git a/src/scanner.l b/src/scanner.l
index 45c6476..59aee8a 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -232,12 +232,16 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 "table"			{ return TABLE; }
 "tables"		{ return TABLES; }
 "chain"			{ return CHAIN; }
+"chains"		{ return CHAINS; }
 "rule"			{ return RULE; }
+"rules"			{ return RULES; }
 "sets"			{ return SETS; }
 "set"			{ return SET; }
 "element"		{ return ELEMENT; }
 "map"			{ return MAP; }
 "handle"		{ return HANDLE; }
+"added"			{ return ADDED; }
+"deleted"		{ return DELETED; }
 
 "accept"		{ return ACCEPT; }
 "drop"			{ return DROP; }
@@ -256,6 +260,7 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 "flush"			{ return FLUSH; }
 "rename"		{ return RENAME; }
 "export"		{ return EXPORT; }
+"monitor"		{ return MONITOR; }
 
 "position"		{ return POSITION; }