[nft PATCH v3 0/4] Implement --echo option

[nft PATCH v3 0/4] Implement --echo option

[Phil Sutter]

Long description of what it is and how it works in patch 3. Patches 1
and 2 are dependencies to patch 3.

I noticed that netlink_events_*_cb() functions accept 'type' parameter
as signed integer, which allows to pass a negative value to enable echo
printing mode without the risk of colliding with one of
nf_tables_msg_types values.

Another change since v2 is a minor fix of the added documentation in
nft.xml - I used <cmd> tag which is not known.

Phil Sutter (4):
  mnl: Consolidate mnl_batch_talk() parameters
  netlink: Pass nlmsg flags from rule.c
  Implement --echo option
  tests: Add a simple test suite for --echo option

 doc/nft.xml                   |  52 +++++++++++++++++
 include/mnl.h                 |   4 +-
 include/netlink.h             |  12 ++--
 include/nftables.h            |   1 +
 src/main.c                    |  11 +++-
 src/mnl.c                     |  31 ++++++++--
 src/netlink.c                 | 133 +++++++++++++++++++++++++++++-------------
 src/rule.c                    |  33 ++++++-----
 tests/echo/run-tests.sh       |  53 +++++++++++++++++
 tests/echo/testcases/simple.t |   8 +++
 10 files changed, 272 insertions(+), 66 deletions(-)
 create mode 100755 tests/echo/run-tests.sh
 create mode 100644 tests/echo/testcases/simple.t

-- 
2.13.1

[nft PATCH v3 1/4] mnl: Consolidate mnl_batch_talk() parameters

[Phil Sutter]

The single caller of this function passes struct netlink_ctx fields as
the first two parameters. This can be simplified by passing the context
object itself and having mnl_batch_talk() access it's fields instead.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 include/mnl.h | 4 ++--
 src/mnl.c     | 6 +++---
 src/netlink.c | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/mnl.h b/include/mnl.h
index 3d2d7fef93ba2..7b1db07bb823e 100644
--- a/include/mnl.h
+++ b/include/mnl.h
@@ -2,6 +2,7 @@
 #define _NFTABLES_MNL_H_
 
 #include <list.h>
+#include <netlink.h>
 
 struct mnl_socket;
 
@@ -24,8 +25,7 @@ bool mnl_batch_ready(struct nftnl_batch *batch);
 void mnl_batch_reset(struct nftnl_batch *batch);
 uint32_t mnl_batch_begin(struct nftnl_batch *batch);
 void mnl_batch_end(struct nftnl_batch *batch);
-int mnl_batch_talk(struct mnl_socket *nl, struct nftnl_batch *batch,
-		   struct list_head *err_list);
+int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list);
 int mnl_nft_rule_batch_add(struct nftnl_rule *nlr, struct nftnl_batch *batch,
 			   unsigned int flags, uint32_t seqnum);
 int mnl_nft_rule_batch_del(struct nftnl_rule *nlr, struct nftnl_batch *batch,
diff --git a/src/mnl.c b/src/mnl.c
index 3db80de6da02d..a3a6bd3fff1e7 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -246,9 +246,9 @@ static ssize_t mnl_nft_socket_sendmsg(const struct mnl_socket *nl,
 	return sendmsg(mnl_socket_get_fd(nl), &msg, 0);
 }
 
-int mnl_batch_talk(struct mnl_socket *nl, struct nftnl_batch *batch,
-		   struct list_head *err_list)
+int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 {
+	struct mnl_socket *nl = ctx->nf_sock;
 	int ret, fd = mnl_socket_get_fd(nl), portid = mnl_socket_get_portid(nl);
 	char rcv_buf[MNL_SOCKET_BUFFER_SIZE];
 	fd_set readfds;
@@ -257,7 +257,7 @@ int mnl_batch_talk(struct mnl_socket *nl, struct nftnl_batch *batch,
 		.tv_usec	= 0
 	};
 
-	ret = mnl_nft_socket_sendmsg(nl, batch);
+	ret = mnl_nft_socket_sendmsg(nl, ctx->batch);
 	if (ret == -1)
 		return -1;
 
diff --git a/src/netlink.c b/src/netlink.c
index 9cef4c48f805a..b4386ad4ecf01 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -1903,7 +1903,7 @@ int netlink_reset_objs(struct netlink_ctx *ctx, const struct handle *h,
 
 int netlink_batch_send(struct netlink_ctx *ctx, struct list_head *err_list)
 {
-	return mnl_batch_talk(ctx->nf_sock, ctx->batch, err_list);
+	return mnl_batch_talk(ctx, err_list);
 }
 
 int netlink_flush_ruleset(struct netlink_ctx *ctx, const struct handle *h,
-- 
2.13.1

[nft PATCH v3 2/4] netlink: Pass nlmsg flags from rule.c

[Phil Sutter]

There is no point in checking value of excl in each called function.
Just do it in a single spot and pass resulting flags.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 include/netlink.h | 10 ++++----
 src/netlink.c     | 69 ++++++++++++++++++++++++++-----------------------------
 src/rule.c        | 26 +++++++++++----------
 3 files changed, 51 insertions(+), 54 deletions(-)

diff --git a/include/netlink.h b/include/netlink.h
index 7865186b62767..ffbc51d352fa0 100644
--- a/include/netlink.h
+++ b/include/netlink.h
@@ -124,7 +124,7 @@ extern int netlink_replace_rule_batch(struct netlink_ctx *ctx,
 
 extern int netlink_add_chain(struct netlink_ctx *ctx, const struct handle *h,
 			     const struct location *loc,
-			     const struct chain *chain, bool excl);
+			     const struct chain *chain, uint32_t flags);
 extern int netlink_rename_chain(struct netlink_ctx *ctx, const struct handle *h,
 				const struct location *loc, const char *name);
 extern int netlink_delete_chain(struct netlink_ctx *ctx, const struct handle *h,
@@ -140,7 +140,7 @@ extern int netlink_flush_chain(struct netlink_ctx *ctx, const struct handle *h,
 
 extern int netlink_add_table(struct netlink_ctx *ctx, const struct handle *h,
 			     const struct location *loc,
-			     const struct table *table, bool excl);
+			     const struct table *table, uint32_t flags);
 extern int netlink_delete_table(struct netlink_ctx *ctx, const struct handle *h,
 				const struct location *loc);
 extern int netlink_list_tables(struct netlink_ctx *ctx, const struct handle *h,
@@ -153,7 +153,7 @@ extern int netlink_flush_table(struct netlink_ctx *ctx, const struct handle *h,
 			       const struct location *loc);
 
 extern int netlink_add_set(struct netlink_ctx *ctx, const struct handle *h,
-			   struct set *set, bool excl);
+			   struct set *set, uint32_t flags);
 extern int netlink_delete_set(struct netlink_ctx *ctx, const struct handle *h,
 			      const struct location *loc);
 extern int netlink_list_sets(struct netlink_ctx *ctx, const struct handle *h,
@@ -165,7 +165,7 @@ extern struct stmt *netlink_parse_set_expr(const struct set *set,
 					   const struct nftnl_expr *nle);
 
 extern int netlink_add_setelems(struct netlink_ctx *ctx, const struct handle *h,
-				const struct expr *expr, bool excl);
+				const struct expr *expr, uint32_t flags);
 extern int netlink_delete_setelems(struct netlink_ctx *ctx, const struct handle *h,
 				   const struct expr *expr);
 extern int netlink_get_setelems(struct netlink_ctx *ctx, const struct handle *h,
@@ -179,7 +179,7 @@ extern int netlink_reset_objs(struct netlink_ctx *ctx, const struct handle *h,
 			      const struct location *loc, uint32_t type,
 			      bool dump);
 extern int netlink_add_obj(struct netlink_ctx *ctx, const struct handle *h,
-			   struct obj *obj, bool excl);
+			   struct obj *obj, uint32_t flags);
 extern int netlink_delete_obj(struct netlink_ctx *ctx, const struct handle *h,
 			      struct location *loc, uint32_t type);
 
diff --git a/src/netlink.c b/src/netlink.c
index b4386ad4ecf01..f13dfd3f9a021 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -447,10 +447,11 @@ int netlink_add_rule_batch(struct netlink_ctx *ctx,
 	struct nftnl_rule *nlr;
 	int err;
 
+	flags |= NLM_F_APPEND | NLM_F_EXCL;
+
 	nlr = alloc_nftnl_rule(&rule->handle);
 	netlink_linearize_rule(ctx, nlr, rule);
-	err = mnl_nft_rule_batch_add(nlr, ctx->batch, flags | NLM_F_EXCL,
-				     ctx->seqnum);
+	err = mnl_nft_rule_batch_add(nlr, ctx->batch, flags, ctx->seqnum);
 	nftnl_rule_free(nlr);
 	if (err < 0)
 		netlink_io_error(ctx, &rule->location,
@@ -597,7 +598,7 @@ void netlink_dump_chain(const struct nftnl_chain *nlc)
 static int netlink_add_chain_compat(struct netlink_ctx *ctx,
 				    const struct handle *h,
 				    const struct location *loc,
-				    const struct chain *chain, bool excl)
+				    const struct chain *chain, uint32_t flags)
 {
 	struct nftnl_chain *nlc;
 	int err;
@@ -618,7 +619,7 @@ static int netlink_add_chain_compat(struct netlink_ctx *ctx,
 	}
 
 	netlink_dump_chain(nlc);
-	err = mnl_nft_chain_add(ctx->nf_sock, nlc, excl ? NLM_F_EXCL : 0);
+	err = mnl_nft_chain_add(ctx->nf_sock, nlc, flags);
 	nftnl_chain_free(nlc);
 
 	if (err < 0)
@@ -630,7 +631,7 @@ static int netlink_add_chain_compat(struct netlink_ctx *ctx,
 static int netlink_add_chain_batch(struct netlink_ctx *ctx,
 				   const struct handle *h,
 				   const struct location *loc,
-				   const struct chain *chain, bool excl)
+				   const struct chain *chain, uint32_t flags)
 {
 	struct nftnl_chain *nlc;
 	int err;
@@ -654,8 +655,7 @@ static int netlink_add_chain_batch(struct netlink_ctx *ctx,
 	}
 
 	netlink_dump_chain(nlc);
-	err = mnl_nft_chain_batch_add(nlc, ctx->batch, excl ? NLM_F_EXCL : 0,
-				      ctx->seqnum);
+	err = mnl_nft_chain_batch_add(nlc, ctx->batch, flags, ctx->seqnum);
 	nftnl_chain_free(nlc);
 
 	if (err < 0)
@@ -666,12 +666,12 @@ static int netlink_add_chain_batch(struct netlink_ctx *ctx,
 
 int netlink_add_chain(struct netlink_ctx *ctx, const struct handle *h,
 		      const struct location *loc, const struct chain *chain,
-		      bool excl)
+		      uint32_t flags)
 {
 	if (ctx->batch_supported)
-		return netlink_add_chain_batch(ctx, h, loc, chain, excl);
+		return netlink_add_chain_batch(ctx, h, loc, chain, flags);
 	else
-		return netlink_add_chain_compat(ctx, h, loc, chain, excl);
+		return netlink_add_chain_compat(ctx, h, loc, chain, flags);
 }
 
 static int netlink_rename_chain_compat(struct netlink_ctx *ctx,
@@ -901,13 +901,13 @@ int netlink_flush_chain(struct netlink_ctx *ctx, const struct handle *h,
 static int netlink_add_table_compat(struct netlink_ctx *ctx,
 				    const struct handle *h,
 				    const struct location *loc,
-				    const struct table *table, bool excl)
+				    const struct table *table, uint32_t flags)
 {
 	struct nftnl_table *nlt;
 	int err;
 
 	nlt = alloc_nftnl_table(h);
-	err = mnl_nft_table_add(ctx->nf_sock, nlt, excl ? NLM_F_EXCL : 0);
+	err = mnl_nft_table_add(ctx->nf_sock, nlt, flags);
 	nftnl_table_free(nlt);
 
 	if (err < 0)
@@ -919,7 +919,7 @@ static int netlink_add_table_compat(struct netlink_ctx *ctx,
 static int netlink_add_table_batch(struct netlink_ctx *ctx,
 				   const struct handle *h,
 				   const struct location *loc,
-				   const struct table *table, bool excl)
+				   const struct table *table, uint32_t flags)
 {
 	struct nftnl_table *nlt;
 	int err;
@@ -930,8 +930,7 @@ static int netlink_add_table_batch(struct netlink_ctx *ctx,
 	else
 		nftnl_table_set_u32(nlt, NFTNL_TABLE_FLAGS, 0);
 
-	err = mnl_nft_table_batch_add(nlt, ctx->batch, excl ? NLM_F_EXCL : 0,
-				      ctx->seqnum);
+	err = mnl_nft_table_batch_add(nlt, ctx->batch, flags, ctx->seqnum);
 	nftnl_table_free(nlt);
 
 	if (err < 0)
@@ -942,12 +941,12 @@ static int netlink_add_table_batch(struct netlink_ctx *ctx,
 
 int netlink_add_table(struct netlink_ctx *ctx, const struct handle *h,
 		      const struct location *loc,
-		      const struct table *table, bool excl)
+		      const struct table *table, uint32_t flags)
 {
 	if (ctx->batch_supported)
-		return netlink_add_table_batch(ctx, h, loc, table, excl);
+		return netlink_add_table_batch(ctx, h, loc, table, flags);
 	else
-		return netlink_add_table_compat(ctx, h, loc, table, excl);
+		return netlink_add_table_compat(ctx, h, loc, table, flags);
 }
 
 static int netlink_del_table_compat(struct netlink_ctx *ctx,
@@ -1228,9 +1227,8 @@ static struct set *netlink_delinearize_set(struct netlink_ctx *ctx,
 
 static int netlink_add_set_compat(struct netlink_ctx *ctx,
 				  const struct handle *h, struct set *set,
-				  bool excl)
+				  uint32_t flags)
 {
-	unsigned int flags = excl ? NLM_F_EXCL : 0;
 	struct nftnl_set *nls;
 	int err;
 
@@ -1261,7 +1259,7 @@ static int netlink_add_set_compat(struct netlink_ctx *ctx,
 
 static int netlink_add_set_batch(struct netlink_ctx *ctx,
 				 const struct handle *h, struct set *set,
-				 bool excl)
+				 uint32_t flags)
 {
 	struct nftnl_udata_buf *udbuf;
 	struct nftnl_set *nls;
@@ -1318,8 +1316,7 @@ static int netlink_add_set_batch(struct netlink_ctx *ctx,
 
 	netlink_dump_set(nls);
 
-	err = mnl_nft_set_batch_add(nls, ctx->batch, excl ? NLM_F_EXCL : 0,
-				    ctx->seqnum);
+	err = mnl_nft_set_batch_add(nls, ctx->batch, flags, ctx->seqnum);
 	if (err < 0)
 		netlink_io_error(ctx, &set->location, "Could not add set: %s",
 				 strerror(errno));
@@ -1329,12 +1326,12 @@ static int netlink_add_set_batch(struct netlink_ctx *ctx,
 }
 
 int netlink_add_set(struct netlink_ctx *ctx, const struct handle *h,
-		    struct set *set, bool excl)
+		    struct set *set, uint32_t flags)
 {
 	if (ctx->batch_supported)
-		return netlink_add_set_batch(ctx, h, set, excl);
+		return netlink_add_set_batch(ctx, h, set, flags);
 	else
-		return netlink_add_set_compat(ctx, h, set, excl);
+		return netlink_add_set_compat(ctx, h, set, flags);
 }
 
 static int netlink_del_set_compat(struct netlink_ctx *ctx,
@@ -1449,7 +1446,7 @@ static void alloc_setelem_cache(const struct expr *set, struct nftnl_set *nls)
 
 static int netlink_add_setelems_batch(struct netlink_ctx *ctx,
 				      const struct handle *h,
-				      const struct expr *expr, bool excl)
+				      const struct expr *expr, uint32_t flags)
 {
 	struct nftnl_set *nls;
 	int err;
@@ -1458,8 +1455,7 @@ static int netlink_add_setelems_batch(struct netlink_ctx *ctx,
 	alloc_setelem_cache(expr, nls);
 	netlink_dump_set(nls);
 
-	err = mnl_nft_setelem_batch_add(nls, ctx->batch, excl ? NLM_F_EXCL : 0,
-					ctx->seqnum);
+	err = mnl_nft_setelem_batch_add(nls, ctx->batch, flags, ctx->seqnum);
 	nftnl_set_free(nls);
 	if (err < 0)
 		netlink_io_error(ctx, &expr->location,
@@ -1470,7 +1466,7 @@ static int netlink_add_setelems_batch(struct netlink_ctx *ctx,
 
 static int netlink_add_setelems_compat(struct netlink_ctx *ctx,
 				       const struct handle *h,
-				       const struct expr *expr, bool excl)
+				       const struct expr *expr, uint32_t flags)
 {
 	struct nftnl_set *nls;
 	int err;
@@ -1479,7 +1475,7 @@ static int netlink_add_setelems_compat(struct netlink_ctx *ctx,
 	alloc_setelem_cache(expr, nls);
 	netlink_dump_set(nls);
 
-	err = mnl_nft_setelem_add(ctx->nf_sock, nls, excl ? NLM_F_EXCL : 0);
+	err = mnl_nft_setelem_add(ctx->nf_sock, nls, flags);
 	nftnl_set_free(nls);
 	if (err < 0)
 		netlink_io_error(ctx, &expr->location,
@@ -1489,12 +1485,12 @@ static int netlink_add_setelems_compat(struct netlink_ctx *ctx,
 }
 
 int netlink_add_setelems(struct netlink_ctx *ctx, const struct handle *h,
-			 const struct expr *expr, bool excl)
+			 const struct expr *expr, uint32_t flags)
 {
 	if (ctx->batch_supported)
-		return netlink_add_setelems_batch(ctx, h, expr, excl);
+		return netlink_add_setelems_batch(ctx, h, expr, flags);
 	else
-		return netlink_add_setelems_compat(ctx, h, expr, excl);
+		return netlink_add_setelems_compat(ctx, h, expr, flags);
 }
 
 static int netlink_del_setelems_batch(struct netlink_ctx *ctx,
@@ -1770,7 +1766,7 @@ void netlink_dump_obj(struct nftnl_obj *nln)
 }
 
 int netlink_add_obj(struct netlink_ctx *ctx, const struct handle *h,
-		    struct obj *obj, bool excl)
+		    struct obj *obj, uint32_t flags)
 {
 	struct nftnl_obj *nlo;
 	int err;
@@ -1778,8 +1774,7 @@ int netlink_add_obj(struct netlink_ctx *ctx, const struct handle *h,
 	nlo = alloc_nftnl_obj(h, obj);
 	netlink_dump_obj(nlo);
 
-	err = mnl_nft_obj_batch_add(nlo, ctx->batch, excl ? NLM_F_EXCL : 0,
-				    ctx->seqnum);
+	err = mnl_nft_obj_batch_add(nlo, ctx->batch, flags, ctx->seqnum);
 	if (err < 0)
 		netlink_io_error(ctx, &obj->location, "Could not add %s: %s",
 				 obj_type_name(obj->type), strerror(errno));
diff --git a/src/rule.c b/src/rule.c
index 7f83980c60818..f8e1b0a460292 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -972,17 +972,17 @@ void cmd_free(struct cmd *cmd)
 #include <netlink.h>
 
 static int __do_add_setelems(struct netlink_ctx *ctx, const struct handle *h,
-			     struct set *set, struct expr *expr, bool excl)
+			     struct set *set, struct expr *expr, uint32_t flags)
 {
 	expr->set_flags |= set->flags;
-	if (netlink_add_setelems(ctx, h, expr, excl) < 0)
+	if (netlink_add_setelems(ctx, h, expr, flags) < 0)
 		return -1;
 
 	return 0;
 }
 
 static int do_add_setelems(struct netlink_ctx *ctx, const struct handle *h,
-			   struct expr *init, bool excl)
+			   struct expr *init, uint32_t flags)
 {
 	struct table *table;
 	struct set *set;
@@ -994,18 +994,18 @@ static int do_add_setelems(struct netlink_ctx *ctx, const struct handle *h,
 	    set_to_intervals(ctx->msgs, set, init, true) < 0)
 		return -1;
 
-	return __do_add_setelems(ctx, h, set, init, excl);
+	return __do_add_setelems(ctx, h, set, init, flags);
 }
 
 static int do_add_set(struct netlink_ctx *ctx, const struct handle *h,
-		      struct set *set, bool excl)
+		      struct set *set, uint32_t flags)
 {
 	if (set->init != NULL) {
 		if (set->flags & NFT_SET_INTERVAL &&
 		    set_to_intervals(ctx->msgs, set, set->init, true) < 0)
 			return -1;
 	}
-	if (netlink_add_set(ctx, h, set, excl) < 0)
+	if (netlink_add_set(ctx, h, set, flags) < 0)
 		return -1;
 	if (set->init != NULL) {
 		return __do_add_setelems(ctx, &set->handle, set, set->init,
@@ -1016,24 +1016,26 @@ static int do_add_set(struct netlink_ctx *ctx, const struct handle *h,
 
 static int do_command_add(struct netlink_ctx *ctx, struct cmd *cmd, bool excl)
 {
+	uint32_t flags = excl ? NLM_F_EXCL : 0;
+
 	switch (cmd->obj) {
 	case CMD_OBJ_TABLE:
 		return netlink_add_table(ctx, &cmd->handle, &cmd->location,
-					 cmd->table, excl);
+					 cmd->table, flags);
 	case CMD_OBJ_CHAIN:
 		return netlink_add_chain(ctx, &cmd->handle, &cmd->location,
-					 cmd->chain, excl);
+					 cmd->chain, flags);
 	case CMD_OBJ_RULE:
 		return netlink_add_rule_batch(ctx, &cmd->handle,
-					      cmd->rule, NLM_F_APPEND);
+					      cmd->rule, flags);
 	case CMD_OBJ_SET:
-		return do_add_set(ctx, &cmd->handle, cmd->set, excl);
+		return do_add_set(ctx, &cmd->handle, cmd->set, flags);
 	case CMD_OBJ_SETELEM:
-		return do_add_setelems(ctx, &cmd->handle, cmd->expr, excl);
+		return do_add_setelems(ctx, &cmd->handle, cmd->expr, flags);
 	case CMD_OBJ_COUNTER:
 	case CMD_OBJ_QUOTA:
 	case CMD_OBJ_CT_HELPER:
-		return netlink_add_obj(ctx, &cmd->handle, cmd->object, excl);
+		return netlink_add_obj(ctx, &cmd->handle, cmd->object, flags);
 	default:
 		BUG("invalid command object type %u\n", cmd->obj);
 	}
-- 
2.13.1

[nft PATCH v3 3/4] Implement --echo option

[Phil Sutter]

When used with add, insert or replace commands, nft tool will print a
string uniquely identifying the new item added to kernel's rule set.

The most beneficial effect of this feature is that it allows to
atomically retrieve an added rule's handle. Previously, one would do
something like this:

| # nft add rule ip t c tcp dport 22 accept
| # handle=$(nft -a list ruleset | \
|            sed -n 's/tcp dport 22 accept # handle \(.*\)/\1/p)

The obvious problem here is that another process might have added the
same rule in between the two commands, so the parsed handle is not
guaranteed to be the right one. Using --echo fixes that:

| # handle=$(nft --echo add rule ip t c tcp dport 22 accept)
| # handle=${handle#*handle }

(Where the second line is just to imitate the above examples behaviour.)

There is a more dramatic problem with any attempt at parsing 'nft list'
output: Some 'nft add' input will never be printed the same way again. A
simple example of this is using mixed port numbers and names:

| nft add rule ip t c tcp dport { ssh, 80 } accept

Depending on number of '-n' flags, the port list will either occur as
all names ("ssh, http") or all numbers ("22, 80").

The idea behind --echo is to print a statement which serves as a unique
identifier suitable for passing to 'nft delete' directly. See the
following examples for illustration:

| # nft --echo add table ip t
| table ip t
| # nft --echo add chain ip t c
| chain ip t c
| # nft --echo add rule ip t c accept
| rule handle 2

In an ideal world, every element and not just rules should have an
identifying handle. When these are added, --echo output can simply be
adjusted to print that handle instead of the name one has to use at the
moment.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
Changes since v1:
- Drop extern declaration of unused variable echo_output.
- Reworded --echo description in man page a bit.

Changes since v2:
- Get rid of NFT_MSG_META_ECHO hack, just use -1 instead.
- Fix for unknown tag <cmd> in nft.xml.
---
 doc/nft.xml        | 52 +++++++++++++++++++++++++++++++++++++++++++++
 include/netlink.h  |  2 ++
 include/nftables.h |  1 +
 src/main.c         | 11 +++++++++-
 src/mnl.c          | 25 ++++++++++++++++++++--
 src/netlink.c      | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 src/rule.c         |  7 +++++-
 7 files changed, 154 insertions(+), 6 deletions(-)

diff --git a/doc/nft.xml b/doc/nft.xml
index 9c9192cf7a8bf..fdef7952e258b 100644
--- a/doc/nft.xml
+++ b/doc/nft.xml
@@ -157,6 +157,17 @@ vi:ts=4 sw=4
 				</listitem>
 			</varlistentry>
 			<varlistentry>
+				<term><option>-e, --echo</option></term>
+				<listitem>
+					<para>
+						When inserting items into the ruleset using <command>add</command>,
+						<command>insert</command> or <command>replace</command> commands,
+						print a line for each item uniquely identifying it, suitable to pass
+						it to a following <command>delete</command> command.
+					</para>
+				</listitem>
+			</varlistentry>
+			<varlistentry>
 				<term><option>-I, --includepath <replaceable>directory</replaceable></option></term>
 				<listitem>
 					<para>
@@ -4421,6 +4432,47 @@ add rule nat prerouting tcp dport 22 redirect to :2222
 	</refsect1>
 
 	<refsect1>
+		<title>Echo Option</title>
+		<para>
+			The flag <option>-e/--echo</option> exists to overcome a practical problem for
+			scripts (or pedantic users) trying to reliably manage their own firewall rules:
+			Although every rule is assigned a unique handle allowing it to be identified later
+			in <command>delete</command> or <command>replace</command> commands, it wasn't
+			possible to retrieve that handle atomically. So one would have to call
+			<command>nft -a list ruleset</command>, parse the output (which may differ from the
+			input sometimes) and still there would be the chance that some other instance
+			inserted a similar rule meanwhile.
+		</para>
+		<para>
+			Using <option>--echo</option> during insertion of a rule (or actually any item)
+			makes <command>nft</command> print a line suitable for passing on to later
+			commands. Here are some examples:
+		</para>
+		<example>
+			<programlisting>
+# nft --echo add table ip t
+table ip t
+# nft --echo add chain ip t c
+chain ip t c
+# nft --echo add set ip t portset '{ type inet_service; }'
+set ip t portset
+# nft --echo add element ip t portset '{ 80, 443 }'
+element ip t portset { http }
+element ip t portset { https }
+# nft --echo add rule ip t c tcp dport @portset drop
+rule ip t c handle 2
+			</programlisting>
+		</example>
+		<para>
+			One might notice that a unique handle exists only for rules - this is not an issue
+			since anything else is uniquely identified by it's name (like tables, chains and
+			sets) or in the case of set elements the element value suffices as there can't be
+			two identical items in a single set (if the element was already there, no line
+			would be printed for it so one doesn't by accident delete elements added by another
+			instance).
+		</para>
+	</refsect1>
+	<refsect1>
 		<title>Error reporting</title>
 		<para>
 			When an error is detected, nft shows the line(s) containing the error, the position
diff --git a/include/netlink.h b/include/netlink.h
index ffbc51d352fa0..47ecef38f9e9d 100644
--- a/include/netlink.h
+++ b/include/netlink.h
@@ -222,4 +222,6 @@ extern int netlink_monitor(struct netlink_mon_handler *monhandler,
 			    struct mnl_socket *nf_sock);
 bool netlink_batch_supported(struct mnl_socket *nf_sock);
 
+int netlink_echo_callback(const struct nlmsghdr *nlh, void *data);
+
 #endif /* NFTABLES_NETLINK_H */
diff --git a/include/nftables.h b/include/nftables.h
index 640d3c7e715d8..ca609015274a9 100644
--- a/include/nftables.h
+++ b/include/nftables.h
@@ -29,6 +29,7 @@ struct output_ctx {
 	unsigned int stateless;
 	unsigned int ip2name;
 	unsigned int handle;
+	unsigned int echo;
 };
 
 struct nft_ctx {
diff --git a/src/main.c b/src/main.c
index 1535153ec815d..86862a1088e0c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -49,10 +49,11 @@ enum opt_vals {
 	OPT_IP2NAME		= 'N',
 	OPT_DEBUG		= 'd',
 	OPT_HANDLE_OUTPUT	= 'a',
+	OPT_ECHO		= 'e',
 	OPT_INVALID		= '?',
 };
 
-#define OPTSTRING	"hvcf:iI:vnsNa"
+#define OPTSTRING	"hvcf:iI:vnsNae"
 
 static const struct option options[] = {
 	{
@@ -105,6 +106,10 @@ static const struct option options[] = {
 		.val		= OPT_HANDLE_OUTPUT,
 	},
 	{
+		.name		= "echo",
+		.val		= OPT_ECHO,
+	},
+	{
 		.name		= NULL
 	}
 };
@@ -128,6 +133,7 @@ static void show_help(const char *name)
 "  -s, --stateless		Omit stateful information of ruleset.\n"
 "  -N				Translate IP addresses to names.\n"
 "  -a, --handle			Output rule handle.\n"
+"  -e, --echo			Echo what has been added, inserted or replaced.\n"
 "  -I, --includepath <directory>	Add <directory> to the paths searched for include files. Default is: %s\n"
 #ifdef DEBUG
 "  --debug <level [,level...]>	Specify debugging level (scanner, parser, eval, netlink, mnl, proto-ctx, segtree, all)\n"
@@ -375,6 +381,9 @@ int main(int argc, char * const *argv)
 		case OPT_HANDLE_OUTPUT:
 			nft.output.handle++;
 			break;
+		case OPT_ECHO:
+			nft.output.echo++;
+			break;
 		case OPT_INVALID:
 			exit(NFT_EXIT_FAILURE);
 		}
diff --git a/src/mnl.c b/src/mnl.c
index a3a6bd3fff1e7..50f006e67c968 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -67,11 +67,32 @@ out:
 	return ret;
 }
 
+struct nft_mnl_talk_cb_data {
+	int (*cb)(const struct nlmsghdr *nlh, void *data);
+	void *data;
+};
+
+static int nft_mnl_talk_cb(const struct nlmsghdr *nlh, void *data)
+{
+	struct nft_mnl_talk_cb_data *cbdata = data;
+	int rc;
+
+	if (cbdata->cb)
+		rc = cbdata->cb(nlh, cbdata->data);
+	if (rc)
+		return rc;
+	return netlink_echo_callback(nlh, cbdata->data);
+}
+
 static int
 nft_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);
+	struct nft_mnl_talk_cb_data tcb_data = {
+		.cb = cb,
+		.data = cb_data,
+	};
 
 #ifdef DEBUG
 	if (debug_level & DEBUG_MNL)
@@ -81,7 +102,7 @@ nft_mnl_talk(struct mnl_socket *nf_sock, const void *data, unsigned int len,
 	if (mnl_socket_sendto(nf_sock, data, len) < 0)
 		return -1;
 
-	return nft_mnl_recv(nf_sock, seq, portid, cb, cb_data);
+	return nft_mnl_recv(nf_sock, seq, portid, &nft_mnl_talk_cb, &tcb_data);
 }
 
 /*
@@ -276,7 +297,7 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 		if (ret == -1)
 			return -1;
 
-		ret = mnl_cb_run(rcv_buf, ret, 0, portid, NULL, NULL);
+		ret = mnl_cb_run(rcv_buf, ret, 0, portid, &netlink_echo_callback, ctx);
 		/* Continue on error, make sure we get all acknowledgments */
 		if (ret == -1)
 			mnl_err_list_node_add(err_list, errno, nlh->nlmsg_seq);
diff --git a/src/netlink.c b/src/netlink.c
index f13dfd3f9a021..35b52a3344f87 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -465,11 +465,11 @@ int netlink_replace_rule_batch(struct netlink_ctx *ctx, const struct handle *h,
 			       const struct location *loc)
 {
 	struct nftnl_rule *nlr;
-	int err;
+	int err, flags = ctx->octx->echo ? NLM_F_ECHO : 0;
 
 	nlr = alloc_nftnl_rule(&rule->handle);
 	netlink_linearize_rule(ctx, nlr, rule);
-	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, 0, ctx->seqnum);
+	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, flags, ctx->seqnum);
 	nftnl_rule_free(nlr);
 
 	if (err < 0)
@@ -2087,6 +2087,8 @@ static int netlink_events_table_cb(const struct nlmsghdr *nlh, int type,
 				printf("update table ");
 			else
 				printf("add table ");
+		} else if (type == -1) {
+			printf("table ");
 		} else {
 			printf("delete table ");
 		}
@@ -2136,6 +2138,12 @@ static int netlink_events_chain_cb(const struct nlmsghdr *nlh, int type,
 			       nftnl_chain_get_str(nlc, NFTNL_CHAIN_TABLE),
 			       nftnl_chain_get_str(nlc, NFTNL_CHAIN_NAME));
 			break;
+		case -1:
+			family = nftnl_chain_get_u32(nlc, NFTNL_CHAIN_FAMILY);
+			printf("chain %s %s %s\n", family2str(family),
+			       nftnl_chain_get_str(nlc, NFTNL_CHAIN_TABLE),
+			       nftnl_chain_get_str(nlc, NFTNL_CHAIN_NAME));
+			break;
 		}
 		break;
 	case NFTNL_OUTPUT_XML:
@@ -2183,6 +2191,13 @@ static int netlink_events_set_cb(const struct nlmsghdr *nlh, int type,
 			       nftnl_set_get_str(nls, NFTNL_SET_TABLE),
 			       nftnl_set_get_str(nls, NFTNL_SET_NAME));
 			break;
+		case -1:
+			family = nftnl_set_get_u32(nls, NFTNL_SET_FAMILY);
+			printf("set %s %s %s\n",
+			       family2str(family),
+			       nftnl_set_get_str(nls, NFTNL_SET_TABLE),
+			       nftnl_set_get_str(nls, NFTNL_SET_NAME));
+			break;
 		}
 		break;
 	case NFTNL_OUTPUT_XML:
@@ -2323,6 +2338,8 @@ static int netlink_events_setelem_cb(const struct nlmsghdr *nlh, int type,
 		case NFT_MSG_DELSETELEM:
 			printf("delete ");
 			break;
+		case -1:
+			break;
 		default:
 			set_free(dummyset);
 			goto out;
@@ -2376,6 +2393,14 @@ static int netlink_events_obj_cb(const struct nlmsghdr *nlh, int type,
 			       nftnl_obj_get_str(nlo, NFTNL_OBJ_TABLE),
 			       nftnl_obj_get_str(nlo, NFTNL_OBJ_NAME));
 			break;
+		case -1:
+			family = nftnl_obj_get_u32(nlo, NFTNL_OBJ_FAMILY);
+			printf("%s %s %s %s\n",
+			       obj_type_name(nftnl_obj_get_u32(nlo, NFTNL_OBJ_TYPE)),
+			       family2str(family),
+			       nftnl_obj_get_str(nlo, NFTNL_OBJ_TABLE),
+			       nftnl_obj_get_str(nlo, NFTNL_OBJ_NAME));
+			break;
 		}
 		break;
 	case NFTNL_OUTPUT_XML:
@@ -2431,6 +2456,10 @@ static int netlink_events_rule_cb(const struct nlmsghdr *nlh, int type,
 			printf("delete rule %s %s %s handle %u\n",
 			       family, table, chain, (unsigned int)handle);
 			break;
+		case -1:
+			printf("rule %s %s %s handle %u\n",
+			       family, table, chain, (unsigned int)handle);
+			break;
 		}
 		break;
 	case NFTNL_OUTPUT_XML:
@@ -3070,6 +3099,35 @@ static int netlink_events_cb(const struct nlmsghdr *nlh, void *data)
 	return ret;
 }
 
+int netlink_echo_callback(const struct nlmsghdr *nlh, void *data)
+{
+	uint16_t type = NFNL_MSG_TYPE(nlh->nlmsg_type);
+	struct netlink_mon_handler echo_monh = {
+		.format = NFTNL_OUTPUT_DEFAULT,
+		.ctx = data,
+		.loc = &netlink_location,
+	};
+
+	if (!echo_monh.ctx->octx->echo)
+		return MNL_CB_OK;
+
+	switch (type) {
+	case NFT_MSG_NEWTABLE:
+		return netlink_events_table_cb(nlh, -1, &echo_monh);
+	case NFT_MSG_NEWCHAIN:
+		return netlink_events_chain_cb(nlh, -1, &echo_monh);
+	case NFT_MSG_NEWSET:
+		return netlink_events_set_cb(nlh, -1, &echo_monh);
+	case NFT_MSG_NEWSETELEM:
+		return netlink_events_setelem_cb(nlh, -1, &echo_monh);
+	case NFT_MSG_NEWRULE:
+		return netlink_events_rule_cb(nlh, -1, &echo_monh);
+	case NFT_MSG_NEWOBJ:
+		return netlink_events_obj_cb(nlh, -1, &echo_monh);
+	}
+	return MNL_CB_OK;
+}
+
 int netlink_monitor(struct netlink_mon_handler *monhandler,
 		     struct mnl_socket *nf_sock)
 {
diff --git a/src/rule.c b/src/rule.c
index f8e1b0a460292..9de38f176e02e 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -1018,6 +1018,9 @@ static int do_command_add(struct netlink_ctx *ctx, struct cmd *cmd, bool excl)
 {
 	uint32_t flags = excl ? NLM_F_EXCL : 0;
 
+	if (ctx->octx->echo)
+		flags |= NLM_F_ECHO;
+
 	switch (cmd->obj) {
 	case CMD_OBJ_TABLE:
 		return netlink_add_table(ctx, &cmd->handle, &cmd->location,
@@ -1056,10 +1059,12 @@ static int do_command_replace(struct netlink_ctx *ctx, struct cmd *cmd)
 
 static int do_command_insert(struct netlink_ctx *ctx, struct cmd *cmd)
 {
+	uint32_t flags = ctx->octx->echo ? NLM_F_ECHO : 0;
+
 	switch (cmd->obj) {
 	case CMD_OBJ_RULE:
 		return netlink_add_rule_batch(ctx, &cmd->handle,
-					      cmd->rule, 0);
+					      cmd->rule, flags);
 	default:
 		BUG("invalid command object type %u\n", cmd->obj);
 	}
-- 
2.13.1

[nft PATCH v3 4/4] tests: Add a simple test suite for --echo option

[Phil Sutter]

The fancy thing about this is that it uses the actual echo output to
undo the changes to the rule set.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 tests/echo/run-tests.sh       | 53 +++++++++++++++++++++++++++++++++++++++++++
 tests/echo/testcases/simple.t |  8 +++++++
 2 files changed, 61 insertions(+)
 create mode 100755 tests/echo/run-tests.sh
 create mode 100644 tests/echo/testcases/simple.t

diff --git a/tests/echo/run-tests.sh b/tests/echo/run-tests.sh
new file mode 100755
index 0000000000000..c10eb47b0d1bb
--- /dev/null
+++ b/tests/echo/run-tests.sh
@@ -0,0 +1,53 @@
+#!/bin/bash
+
+cd $(dirname $0)
+nft=../../src/nft
+debug=false
+
+debug_echo() {
+	$debug || return
+
+	echo "$@"
+}
+
+undo_file=$(mktemp)
+
+undo() {
+	[[ -f $undo_file ]] || return
+	tac $undo_file | while read line; do
+		debug_echo "undo: '$nft delete $line'"
+		$nft delete $line || {
+			echo "Warning: undo failed for line '$line'"
+		}
+	done
+	rm $undo_file
+}
+
+trap undo EXIT
+
+for testcase in testcases/*.t; do
+	echo "running tests from file $(basename $testcase)"
+	# files are like this:
+	#
+	# <input command>;<output regexp>
+
+	while read line; do
+		[[ -z "$line" || "$line" == "#"* ]] && continue
+
+		# XXX: this only works if there is no semicolon in output
+		input="${line%;*}"
+		output="${line##*;}"
+
+		debug_echo "calling '$nft --echo $input'"
+		cmd_out=$($nft --echo $input)
+		debug_echo "got output '$cmd_out'"
+		[[ $cmd_out == $output ]] || {
+			echo "Warning: Output differs:"
+			echo "# nft --echo $input"
+			echo "- $output"
+			echo "+ $cmd_out"
+		}
+		echo "$cmd_out" >> $undo_file
+	done <$testcase
+	undo
+done
diff --git a/tests/echo/testcases/simple.t b/tests/echo/testcases/simple.t
new file mode 100644
index 0000000000000..bf8857dc5e858
--- /dev/null
+++ b/tests/echo/testcases/simple.t
@@ -0,0 +1,8 @@
+add table ip t;table ip t
+add chain ip t c;chain ip t c
+add rule ip t c accept;rule ip t c handle *
+
+add set ip t ipset {type ipv4_addr; };set ip t ipset
+add element ip t ipset { 192.168.0.1 };element ip t ipset { 192.168.0.1 }
+
+add counter ip t cnt;counter ip t cnt
-- 
2.13.1

Re: [nft PATCH v3 1/4] mnl: Consolidate mnl_batch_talk() parameters

[Pablo Neira Ayuso]

On Fri, Jul 28, 2017 at 01:55:45PM +0200, Phil Sutter wrote:
> The single caller of this function passes struct netlink_ctx fields as
> the first two parameters. This can be simplified by passing the context
> object itself and having mnl_batch_talk() access it's fields instead.

Applied, thanks.

Re: [nft PATCH v3 2/4] netlink: Pass nlmsg flags from rule.c

[Pablo Neira Ayuso]

On Fri, Jul 28, 2017 at 01:55:46PM +0200, Phil Sutter wrote:
> There is no point in checking value of excl in each called function.
> Just do it in a single spot and pass resulting flags.

Also applied, thanks.

Re: [nft PATCH v3 3/4] Implement --echo option

[Pablo Neira Ayuso]

On Fri, Jul 28, 2017 at 01:55:47PM +0200, Phil Sutter wrote:
[...]
> diff --git a/src/netlink.c b/src/netlink.c
> index f13dfd3f9a021..35b52a3344f87 100644
> --- a/src/netlink.c
> +++ b/src/netlink.c
> @@ -465,11 +465,11 @@ int netlink_replace_rule_batch(struct netlink_ctx *ctx, const struct handle *h,
>  			       const struct location *loc)
>  {
>  	struct nftnl_rule *nlr;
> -	int err;
> +	int err, flags = ctx->octx->echo ? NLM_F_ECHO : 0;
>  
>  	nlr = alloc_nftnl_rule(&rule->handle);
>  	netlink_linearize_rule(ctx, nlr, rule);
> -	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, 0, ctx->seqnum);
> +	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, flags, ctx->seqnum);
>  	nftnl_rule_free(nlr);
>  
>  	if (err < 0)
> @@ -2087,6 +2087,8 @@ static int netlink_events_table_cb(const struct nlmsghdr *nlh, int type,
>  				printf("update table ");
>  			else
>  				printf("add table ");
> +		} else if (type == -1) {
> +			printf("table ");

Why do we need this '-1' case? Same question for other objects.

Thanks!

Re: [nft PATCH v3 2/4] netlink: Pass nlmsg flags from rule.c

[Pablo Neira Ayuso]

On Wed, Aug 02, 2017 at 02:36:40PM +0200, Pablo Neira Ayuso wrote:
> On Fri, Jul 28, 2017 at 01:55:46PM +0200, Phil Sutter wrote:
> > There is no point in checking value of excl in each called function.
> > Just do it in a single spot and pass resulting flags.
> 
> Also applied, thanks.

Oops. I have to keep this back, sorry.

It breaks testcases/rule_management/0003insert_0.

Please run tests before submitting, thanks!

Re: [nft PATCH v3 3/4] Implement --echo option

[Pablo Neira Ayuso]

On Wed, Aug 02, 2017 at 02:37:44PM +0200, Pablo Neira Ayuso wrote:
> On Fri, Jul 28, 2017 at 01:55:47PM +0200, Phil Sutter wrote:
> [...]
> > diff --git a/src/netlink.c b/src/netlink.c
> > index f13dfd3f9a021..35b52a3344f87 100644
> > --- a/src/netlink.c
> > +++ b/src/netlink.c
> > @@ -465,11 +465,11 @@ int netlink_replace_rule_batch(struct netlink_ctx *ctx, const struct handle *h,
> >  			       const struct location *loc)
> >  {
> >  	struct nftnl_rule *nlr;
> > -	int err;
> > +	int err, flags = ctx->octx->echo ? NLM_F_ECHO : 0;
> >  
> >  	nlr = alloc_nftnl_rule(&rule->handle);
> >  	netlink_linearize_rule(ctx, nlr, rule);
> > -	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, 0, ctx->seqnum);
> > +	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, flags, ctx->seqnum);
> >  	nftnl_rule_free(nlr);
> >  
> >  	if (err < 0)
> > @@ -2087,6 +2087,8 @@ static int netlink_events_table_cb(const struct nlmsghdr *nlh, int type,
> >  				printf("update table ");
> >  			else
> >  				printf("add table ");
> > +		} else if (type == -1) {
> > +			printf("table ");
> 
> Why do we need this '-1' case? Same question for other objects.

This is there just to skip the "add ..." part of the string, right?

I think this is relevant information. Semantically, this is just
exposing the netlink NLM_F_ECHO flag, so it should be possible to use
this flag in the future with 'delete' commands.

So if this -1 type is there just to skip the "add ...", I would simply
remove it.

Thanks!

Re: [nft PATCH v3 2/4] netlink: Pass nlmsg flags from rule.c

[Phil Sutter]

On Wed, Aug 02, 2017 at 02:58:57PM +0200, Pablo Neira Ayuso wrote:
> On Wed, Aug 02, 2017 at 02:36:40PM +0200, Pablo Neira Ayuso wrote:
> > On Fri, Jul 28, 2017 at 01:55:46PM +0200, Phil Sutter wrote:
> > > There is no point in checking value of excl in each called function.
> > > Just do it in a single spot and pass resulting flags.
> > 
> > Also applied, thanks.
> 
> Oops. I have to keep this back, sorry.
> 
> It breaks testcases/rule_management/0003insert_0.

Oh, it breaks insert command for rules.

> Please run tests before submitting, thanks!

Will do, sorry!

Thanks, Phil

Re: [nft PATCH v3 3/4] Implement --echo option

[Phil Sutter]

On Wed, Aug 02, 2017 at 03:18:04PM +0200, Pablo Neira Ayuso wrote:
> On Wed, Aug 02, 2017 at 02:37:44PM +0200, Pablo Neira Ayuso wrote:
> > On Fri, Jul 28, 2017 at 01:55:47PM +0200, Phil Sutter wrote:
> > [...]
> > > diff --git a/src/netlink.c b/src/netlink.c
> > > index f13dfd3f9a021..35b52a3344f87 100644
> > > --- a/src/netlink.c
> > > +++ b/src/netlink.c
> > > @@ -465,11 +465,11 @@ int netlink_replace_rule_batch(struct netlink_ctx *ctx, const struct handle *h,
> > >  			       const struct location *loc)
> > >  {
> > >  	struct nftnl_rule *nlr;
> > > -	int err;
> > > +	int err, flags = ctx->octx->echo ? NLM_F_ECHO : 0;
> > >  
> > >  	nlr = alloc_nftnl_rule(&rule->handle);
> > >  	netlink_linearize_rule(ctx, nlr, rule);
> > > -	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, 0, ctx->seqnum);
> > > +	err = mnl_nft_rule_batch_replace(nlr, ctx->batch, flags, ctx->seqnum);
> > >  	nftnl_rule_free(nlr);
> > >  
> > >  	if (err < 0)
> > > @@ -2087,6 +2087,8 @@ static int netlink_events_table_cb(const struct nlmsghdr *nlh, int type,
> > >  				printf("update table ");
> > >  			else
> > >  				printf("add table ");
> > > +		} else if (type == -1) {
> > > +			printf("table ");
> > 
> > Why do we need this '-1' case? Same question for other objects.
> 
> This is there just to skip the "add ..." part of the string, right?
> 
> I think this is relevant information. Semantically, this is just
> exposing the netlink NLM_F_ECHO flag, so it should be possible to use
> this flag in the future with 'delete' commands.
> 
> So if this -1 type is there just to skip the "add ...", I would simply
> remove it.

Yes, exactly. This is what I had in mind when I started with this
series, back when it was merely about atomic handle retrieval by
supporting '-a' flag in add/insert/replace commands for rules. Changing
the whole concept into this generic --echo option was your idea. :)

But OK, since most of the original idea is lost now anyway, I can get
rid of this last bit as well.

Cheers, Phil