[PATCH nftables 3/3] src: mnl: retry when we hit -ENOBUFS

[Florian Westphal <fw@strlen.de>]

tests/shell/testcases/transactions/0049huge_0

still fails with ENOBUFS error after endian fix done in
previous patch.  Its enough to increase the scale factor (4)
on s390x, but rather than continue with these "guess the proper
size" game, just increase the buffer size and retry up to 3 times.

This makes above test work on s390x.

So, implement what Pablo suggested in the earlier commit:
    We could also explore increasing the buffer and retry if
    mnl_nft_socket_sendmsg() hits ENOBUFS if we ever hit this problem again.

v2: call setsockopt unconditionally, then increase on error.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/mnl.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/mnl.c b/src/mnl.c
index 97a2e0765189..9c1f5356c9b9 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -311,6 +311,7 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
 	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];
+	unsigned int enobuf_restarts = 0;
 	size_t avg_msg_size, batch_size;
 	const struct sockaddr_nl snl = {
 		.nl_family = AF_NETLINK
@@ -320,6 +321,7 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
 		.tv_usec	= 0
 	};
 	struct iovec iov[iov_len];
+	unsigned int scale = 4;
 	struct msghdr msg = {};
 	fd_set readfds;
 
@@ -328,7 +330,8 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
 	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);
+restart:
+	mnl_set_rcvbuffer(ctx->nft->nf_sock, num_cmds * avg_msg_size * scale);
 
 	ret = mnl_nft_socket_sendmsg(ctx, &msg);
 	if (ret == -1)
@@ -347,8 +350,13 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
 			break;
 
 		ret = mnl_socket_recvfrom(nl, rcv_buf, sizeof(rcv_buf));
-		if (ret == -1)
+		if (ret == -1) {
+			if (errno == ENOBUFS && enobuf_restarts++ < 3) {
+				scale *= 2;
+				goto restart;
+			}
 			return -1;
+		}
 
 		ret = mnl_cb_run(rcv_buf, ret, 0, portid, &netlink_echo_callback, ctx);
 		/* Continue on error, make sure we get all acknowledgments */
-- 
2.21.0