From 1dd5cd1706b7012ab89907bf1f15dc9a1b17f98e Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Thu, 15 Jul 2021 19:52:14 +0200
Subject: [PATCH] respondd-module-airtime: improve error handling

- Return either NL_OK or NL_STOP from callback
- Return the generated airtime entry from get_airtime()
---
 net/respondd-module-airtime/src/airtime.c  | 36 ++++++++++++++--------
 net/respondd-module-airtime/src/airtime.h  |  3 +-
 net/respondd-module-airtime/src/respondd.c | 14 +++------
 3 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/net/respondd-module-airtime/src/airtime.c b/net/respondd-module-airtime/src/airtime.c
index 7e27ee0..7f03f1b 100644
--- a/net/respondd-module-airtime/src/airtime.c
+++ b/net/respondd-module-airtime/src/airtime.c
@@ -67,20 +67,26 @@ static const char const* msg_names[NL80211_SURVEY_INFO_MAX + 1] = {
 };
 
 static int survey_airtime_handler(struct nl_msg *msg, void *arg) {
-	struct json_object *parent_json = (struct json_object *) arg;
+	struct json_object **result = arg;
+	struct json_object *freq_json = NULL;
 
 	struct genlmsghdr *gnlh = nlmsg_data(nlmsg_hdr(msg));
 	struct nlattr *survey_info = nla_find(genlmsg_attrdata(gnlh, 0), genlmsg_attrlen(gnlh, 0), NL80211_ATTR_SURVEY_INFO);
 
-	if (!survey_info) {
-		fprintf(stderr, "respondd-module-airtime: survey data missing in netlink message\n");
-		goto abort;
+	if (*result) {
+		fprintf(stderr, "respondd-module-airtime: callback called again after NL_STOP\n");
+		return NL_STOP;
 	}
 
-	struct json_object *freq_json = json_object_new_object();
+	if (!survey_info) {
+		fprintf(stderr, "respondd-module-airtime: survey data missing in netlink message\n");
+		return NL_STOP;
+	}
+
+	freq_json = json_object_new_object();
 	if (!freq_json) {
 		fprintf(stderr, "respondd-module-airtime: failed allocating JSON object\n");
-		goto abort;
+		return NL_STOP;
 	}
 
 	// This variable counts the number of required attributes that are
@@ -129,15 +135,19 @@ static int survey_airtime_handler(struct nl_msg *msg, void *arg) {
 			json_object_object_add(freq_json, msg_names[type], data_json);
 	}
 
-	if (req_fields == 3)
-		json_object_array_add(parent_json, freq_json);
-	else
+	/* The kernel didn't report all required fields: continue with next
+	 * record, this entry was off-channel */
+	if (req_fields != 3) {
 		json_object_put(freq_json);
+		return NL_OK;
+	}
 
-abort:
-	return NL_SKIP;
+	*result = freq_json;
+	return NL_STOP;
 }
 
-bool get_airtime(struct json_object *result, int ifx) {
-	return nl_send_dump(survey_airtime_handler, result, NL80211_CMD_GET_SURVEY, ifx);
+struct json_object * get_airtime(int ifx) {
+	struct json_object *result = NULL;
+	nl_send_dump(survey_airtime_handler, &result, NL80211_CMD_GET_SURVEY, ifx);
+	return result;
 }
diff --git a/net/respondd-module-airtime/src/airtime.h b/net/respondd-module-airtime/src/airtime.h
index 7adc91e..7db21ec 100644
--- a/net/respondd-module-airtime/src/airtime.h
+++ b/net/respondd-module-airtime/src/airtime.h
@@ -4,4 +4,5 @@
 #include <stdint.h>
 #include <json-c/json.h>
 
-__attribute__((visibility("hidden"))) bool get_airtime(struct json_object *result, int ifx);
+__attribute__((visibility("hidden")))
+struct json_object * get_airtime(int ifx);
diff --git a/net/respondd-module-airtime/src/respondd.c b/net/respondd-module-airtime/src/respondd.c
index eaf8182..6555835 100644
--- a/net/respondd-module-airtime/src/respondd.c
+++ b/net/respondd-module-airtime/src/respondd.c
@@ -7,9 +7,7 @@
 #include "ifaces.h"
 
 static struct json_object *respondd_provider_statistics(void) {
-	bool ok;
-	int newest_element_index;
-	struct json_object *last, *result, *wireless;
+	struct json_object *result, *wireless;
 	struct iface_list *ifaces;
 
 	result = json_object_new_object();
@@ -24,12 +22,10 @@ static struct json_object *respondd_provider_statistics(void) {
 
 	ifaces = get_ifaces();
 	while (ifaces != NULL) {
-		ok = get_airtime(wireless, ifaces->ifx);
-		if (ok) {
-			newest_element_index = json_object_array_length(wireless) - 1;
-			last = json_object_array_get_idx(wireless, newest_element_index);
-			if (last)
-				json_object_object_add(last, "phy", json_object_new_int(ifaces->wiphy));
+		struct json_object *entry = get_airtime(ifaces->ifx);
+		if (entry) {
+			json_object_object_add(entry, "phy", json_object_new_int(ifaces->wiphy));
+			json_object_array_add(wireless, entry);
 		}
 		void *freeptr = ifaces;
 		ifaces = ifaces->next;