From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Wed, 29 May 2019 18:23:23 +0000 (+0200)
Subject: mnl: estimate receiver buffer size
X-Git-Tag: v0.9.1~57
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=89c82c261bb53bfb0b671437a1323830dd7e4019;p=thirdparty%2Fnftables.git

mnl: estimate receiver buffer size

Set a receiver buffer size based on the number of commands and the
average message size, this is useful for the --echo option in order to
avoid ENOBUFS errors.

On the kernel side, each skbuff consumes truesize from the socket queue
(although it uses NLMSG_GOODSIZE to allocate it), which is approximately
four times the estimated size per message that we get in turn for each
echo message to ensure enough receiver buffer space.

We could also explore increasing the buffer and retry if
mnl_nft_socket_sendmsg() hits ENOBUFS if we ever hit this problem again.

Reported-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---

diff --git a/include/mnl.h b/include/mnl.h
index c63a7e7f..9f50c3da 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 199dbc97..a58b8ca9 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 e70f8b39..4f6f43d2 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -299,12 +299,14 @@ static ssize_t mnl_nft_socket_sendmsg(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);
 	uint32_t iov_len = nftnl_batch_iovec_len(ctx->batch);
 	char rcv_buf[MNL_SOCKET_BUFFER_SIZE];
+	size_t avg_msg_size, batch_size;
 	const struct sockaddr_nl snl = {
 		.nl_family = AF_NETLINK
 	};
@@ -319,7 +321,10 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 
 	mnl_set_sndbuffer(ctx->nft->nf_sock, ctx->batch);
 
-	mnl_nft_batch_to_msg(ctx, &msg, &snl, iov, iov_len);
+	batch_size = mnl_nft_batch_to_msg(ctx, &msg, &snl, iov, iov_len);
+	avg_msg_size = div_round_up(batch_size, num_cmds);
+
+	mnl_set_rcvbuffer(ctx->nft->nf_sock, num_cmds * avg_msg_size * 4);
 
 	ret = mnl_nft_socket_sendmsg(ctx, &msg);
 	if (ret == -1)