Here's a simple iw patch that shows the error message string:
--- a/iw.c
+++ b/iw.c
@@ -62,6 +62,10 @@ static int nl80211_init(struct nl80211_state *state)
nl_socket_set_buffer_size(state->nl_sock, 8192, 8192);
+ /* try to set NETLINK_EXT_ACK to 1 (ignore errors) */
+ err = 1;
+ setsockopt(nl_socket_get_fd(state->nl_sock), SOL_NETLINK, 11, &err,
sizeof(err));
+
state->nl80211_id = genl_ctrl_resolve(state->nl_sock, "nl80211");
if (state->nl80211_id < 0) {
fprintf(stderr, "nl80211 not found.\n");
@@ -270,11 +274,45 @@ static int phy_lookup(char *name)
return atoi(buf);
}
+#ifndef NETLINK_EXT_ACK
+enum nlmsgerr_attrs {
+ NLMSGERR_ATTR_UNUSED,
+ NLMSGERR_ATTR_MSG,
+ NLMSGERR_ATTR_OFFS,
+ NLMSGERR_ATTR_ATTR,
+ NLMSGERR_ATTR_COOKIE,
+
+ NUM_NLMSGERR_ATTRS,
+ NLMSGERR_ATTR_MAX = NUM_NLMSGERR_ATTRS - 1
+};
+#endif
+
static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err,
void *arg)
{
+ struct nlmsghdr *nlh = (struct nlmsghdr *)err - 1;
+ int len = nlh->nlmsg_len;
+ struct nlattr *attrs;
+ struct nlattr *tb[NUM_NLMSGERR_ATTRS];
int *ret = arg;
+ int ack_len = sizeof(*nlh) + sizeof(int) + err->msg.nlmsg_len;
+
*ret = err->error;
+
+ if (len <= ack_len)
+ return NL_STOP;
+
+ attrs = (void *)((unsigned char *)nlh + ack_len);
+ len -= ack_len;
+
+ nla_parse(tb, NLMSGERR_ATTR_MAX, attrs, len, NULL);
+ if (tb[NLMSGERR_ATTR_MSG]) {
+ len = strnlen((char *)nla_data(tb[NLMSGERR_ATTR_MSG]),
+ nla_len(tb[NLMSGERR_ATTR_MSG]));
+ fprintf(stderr, "kernel reports: %*s\n", len,
+ (char *)nla_data(tb[NLMSGERR_ATTR_MSG]));
+ }
+
return NL_STOP;
}
johannes
