platform: print error message from netlink extended ackbg/extack

From v4.12 the kernel appends some attributes to netlink acks
containing a textual description of the error and other fields (see
commit [1]). Parse those attributes and print the error message.

Example:

platform-linux: netlink: recvmsg: error message from kernel: Network is unreachable (101) "Nexthop has invalid gateway" for request 12

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2d4bc93368f5a0ddb57c8c885cdad9c9b7a10ed5

1 files changed, 20 insertions, 0 deletions

diff --git a/src/platform/nm-netlink.c b/src/platform/nm-netlink.c
index 7d794f7737..0baaaf0b47 100644
--- a/src/platform/nm-netlink.c
+++ b/src/platform/nm-netlink.c
@@ -38,6 +38,10 @@
 #define NL_MSG_PEEK_EXPLICIT    (1<<4)
 #define NL_NO_AUTO_ACK          (1<<5)
 
+#ifndef NETLINK_EXT_ACK
+#define NETLINK_EXT_ACK         11
+#endif
+
 #define NL_MSG_CRED_PRESENT 1
 
 struct nl_msg {
@@ -933,6 +937,22 @@ nl_socket_add_memberships (struct nl_sock *sk, int group, ...)
 	return 0;
 }
 
+int
+nl_socket_set_ext_ack (struct nl_sock *sk, gboolean enable)
+{
+	int err;
+
+	if (sk->s_fd == -1)
+		return -NLE_BAD_SOCK;
+
+	enable = !!enable;
+	err = setsockopt (sk->s_fd, SOL_NETLINK, NETLINK_EXT_ACK, &enable, sizeof (enable));
+	if (err < 0)
+		return -nl_syserr2nlerr (errno);
+
+	return 0;
+}
+
 void nl_socket_disable_msg_peek (struct nl_sock *sk)
 {
 	sk->s_flags |= NL_MSG_PEEK_EXPLICIT;