[PATCH iproute2] dcb: unblock mnl_socket_recvfrom if not message received

[Hao Lan <lanhao@huawei.com>]

From: Junxin Chen <chenjunxin1@huawei.com>

Currently, the dcb command sinks to the kernel through the netlink
to obtain information. However, if the kernel fails to obtain infor-
mation or is not processed, the dcb command is suspended.

For example, if we don't implement dcbnl_ops->ieee_getpfc in the
kernel, the command "dcb pfc show dev eth1" will be stuck and subsequent
commands cannot be executed.

This patch adds the NLM_F_ACK flag to the netlink in mnlu_msg_prepare
to ensure that the kernel responds to user requests.

After the problem is solved, the execution result is as follows:
$ dcb pfc show dev eth1
Attribute not found: Success

Fixes: 67033d1c1c ("Add skeleton of a new tool, dcb")
Signed-off-by: Junxin Chen <chenjunxin1@huawei.com>
---
 dcb/dcb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dcb/dcb.c b/dcb/dcb.c
index 8d75ab0a..a6f457fb 100644
--- a/dcb/dcb.c
+++ b/dcb/dcb.c
@@ -156,7 +156,7 @@ static struct nlmsghdr *dcb_prepare(struct dcb *dcb, const char *dev,
 	};
 	struct nlmsghdr *nlh;
 
-	nlh = mnlu_msg_prepare(dcb->buf, nlmsg_type, NLM_F_REQUEST, &dcbm, sizeof(dcbm));
+	nlh = mnlu_msg_prepare(dcb->buf, nlmsg_type, NLM_F_REQUEST | NLM_F_ACK, &dcbm, sizeof(dcbm));
 	mnl_attr_put_strz(nlh, DCB_ATTR_IFNAME, dev);
 	return nlh;
 }
-- 
2.33.0