[iptables PATCH] nft: Increase BATCH_PAGE_SIZE to support huge rulesets

[Phil Sutter <phil@nwl.cc>]

In order to support the same ruleset sizes as legacy iptables, the
kernel's limit of 1024 iovecs has to be overcome. Therefore increase
each iovec's size from 256KB to 4MB.

While being at it, add a log message for failing sendmsg() call. This is
not supposed to happen, even if the transaction fails. Yet if it does,
users are left with only a "line XXX failed" message (with line number
being the COMMIT line).

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 iptables/nft.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/iptables/nft.c b/iptables/nft.c
index bd840e75f83f4..e19c88ece6c2a 100644
--- a/iptables/nft.c
+++ b/iptables/nft.c
@@ -88,11 +88,11 @@ int mnl_talk(struct nft_handle *h, struct nlmsghdr *nlh,
 
 #define NFT_NLMSG_MAXSIZE (UINT16_MAX + getpagesize())
 
-/* selected batch page is 256 Kbytes long to load ruleset of
- * half a million rules without hitting -EMSGSIZE due to large
- * iovec.
+/* Selected batch page is 4 Mbytes long to support loading a ruleset of 3.5M
+ * rules matching on source and destination address as well as input and output
+ * interfaces. This is what legacy iptables supports.
  */
-#define BATCH_PAGE_SIZE getpagesize() * 32
+#define BATCH_PAGE_SIZE getpagesize() * 512
 
 static struct nftnl_batch *mnl_batch_init(void)
 {
@@ -220,8 +220,10 @@ static int mnl_batch_talk(struct nft_handle *h, int numcmds)
 	int err = 0;
 
 	ret = mnl_nft_socket_sendmsg(h, numcmds);
-	if (ret == -1)
+	if (ret == -1) {
+		fprintf(stderr, "sendmsg() failed: %s\n", strerror(errno));
 		return -1;
+	}
 
 	FD_ZERO(&readfds);
 	FD_SET(fd, &readfds);
-- 
2.31.0