[PATCH nft 3/3] mnl: estimate receiver buffer size based on the number of commands

[Pablo Neira Ayuso <pablo@netfilter.org>]

Set a receiver buffer size based on the number of commands, this is
useful for the --echo option in order to avoid ENOBUFS errors, assume
MNL_SOCKET_BUFFER_SIZE per echo message worst case.

Reported-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/mnl.h     | 3 ++-
 src/libnftables.c | 5 +++--
 src/mnl.c         | 6 ++++--
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/mnl.h b/include/mnl.h
index c63a7e7fd73a..9f50c3da0f3a 100644
--- a/include/mnl.h
+++ b/include/mnl.h
@@ -25,7 +25,8 @@ 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, uint32_t seqnum);
 void mnl_batch_end(struct nftnl_batch *batch, uint32_t seqnum);
-int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list);
+int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
+		   uint32_t num_cmds);
 
 int mnl_nft_rule_add(struct netlink_ctx *ctx, const struct cmd *cmd,
 		     unsigned int flags);
diff --git a/src/libnftables.c b/src/libnftables.c
index 199dbc97b801..a58b8ca9dcf6 100644
--- a/src/libnftables.c
+++ b/src/libnftables.c
@@ -21,7 +21,7 @@ static int nft_netlink(struct nft_ctx *nft,
 		       struct list_head *cmds, struct list_head *msgs,
 		       struct mnl_socket *nf_sock)
 {
-	uint32_t batch_seqnum, seqnum = 0;
+	uint32_t batch_seqnum, seqnum = 0, num_cmds = 0;
 	struct nftnl_batch *batch;
 	struct netlink_ctx ctx;
 	struct cmd *cmd;
@@ -49,6 +49,7 @@ static int nft_netlink(struct nft_ctx *nft,
 					 strerror(errno));
 			goto out;
 		}
+		num_cmds++;
 	}
 	if (!nft->check)
 		mnl_batch_end(batch, mnl_seqnum_alloc(&seqnum));
@@ -56,7 +57,7 @@ static int nft_netlink(struct nft_ctx *nft,
 	if (!mnl_batch_ready(batch))
 		goto out;
 
-	ret = mnl_batch_talk(&ctx, &err_list);
+	ret = mnl_batch_talk(&ctx, &err_list, num_cmds);
 
 	list_for_each_entry_safe(err, tmp, &err_list, head) {
 		list_for_each_entry(cmd, cmds, list) {
diff --git a/src/mnl.c b/src/mnl.c
index e623a1adccfc..e9419ce6cd76 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -278,19 +278,21 @@ static ssize_t mnl_nft_socket_sendmsg(const struct netlink_ctx *ctx)
 	return sendmsg(mnl_socket_get_fd(ctx->nft->nf_sock), &msg, 0);
 }
 
-int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
+int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
+		   uint32_t num_cmds)
 {
 	struct mnl_socket *nl = ctx->nft->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;
 	struct timeval tv = {
 		.tv_sec		= 0,
 		.tv_usec	= 0
 	};
+	fd_set readfds;
 	int err = 0;
 
 	mnl_set_sndbuffer(ctx->nft->nf_sock, ctx->batch);
+	mnl_set_rcvbuffer(ctx->nft->nf_sock, num_cmds * MNL_SOCKET_BUFFER_SIZE);
 
 	ret = mnl_nft_socket_sendmsg(ctx);
 	if (ret == -1)
-- 
2.11.0