Handle -k better on platforms that don't support it.

Have ws80211_init() return an indication that channel setting isn't
supported on those platforms.

In dumpcap, try to set up ws80211 before checking the channel argument
and, if it fails, report the failure, rather than failing because the
"convert channel name to channel code" routine fails.

See

    https://ask.wireshark.org/question/15535/dumpcap-k-is-not-accepting-channel-type-values/

for an example of confusion caused by the previous behavior.

Change-Id: I303f560704700bbcd4f0ecea041f8632744212f3
Reviewed-on: https://code.wireshark.org/review/36659
Petri-Dish: Guy Harris <[email protected]>
Tested-by: Petri Dish Buildbot
Reviewed-by: Guy Harris <[email protected]>

caputils/ws80211_utils.c

@@ -102,7 +102,7 @@ int ws80211_init(void)
 		state->have_split_wiphy = TRUE;
 #endif /* HAVE_NL80211_SPLIT_WIPHY_DUMP */
 
-	return 0;
+	return WS80211_INIT_OK;
 
  out_handle_destroy:
 	nl_socket_free(state->nl_sock);
@@ -933,9 +933,9 @@ const char *ws80211_get_helper_path(void) {
 int ws80211_init(void)
 {
 	if (airpcap_get_dll_state() == AIRPCAP_DLL_OK) {
-		return 0;
+		return WS80211_INIT_OK;
 	}
-	return -1;
+	return WS80211_INIT_NOT_SUPPORTED;
 }
 
 static const char *airpcap_dev_prefix_ = "\\\\.\\";
@@ -1198,7 +1198,7 @@ const char *ws80211_get_helper_path(void)
 #else /* Everyone else. */
 int ws80211_init(void)
 {
-	return -1;
+	return WS80211_INIT_NOT_SUPPORTED;
 }
 
 GArray* ws80211_find_interfaces(void)

caputils/ws80211_utils.h

@@ -65,8 +65,13 @@ struct ws80211_iface_info {
  * On Windows this checks the AirPcap status. It does *not* load the
  * AirPcap DLL. That happens when the program starts.
  *
- * @return 0 on success, an error value on failure.
+ * @return WS80211_INIT_OK on success, WS80211_INIT_NOT_SUPPORTED if the
+ * 802.11 environment isn't supported, or the negative of an errno value
+ * on failure.
  */
+#define WS80211_INIT_OK            0
+#define WS80211_INIT_NOT_SUPPORTED 1
+
 int ws80211_init(void);
 
 /** Build a list of 802.11 interfaces.

dumpcap.c

@@ -4464,7 +4464,18 @@ set_80211_channel(const char *iface, const char *opt)
     gchar **options = NULL;
 
     options = g_strsplit_set(opt, ",", 4);
-    for (args = 0; options[args]; args++);
+    for (args = 0; options[args]; args++)
+        ;
+
+    ret = ws80211_init();
+    if (ret != WS80211_INIT_OK) {
+        if (ret == WS80211_INIT_NOT_SUPPORTED)
+            cmdarg_err("Setting 802.11 channels is not supported on this platform");
+        else
+            cmdarg_err("Failed to init ws80211: %s", g_strerror(abs(ret)));
+        ret = 2;
+        goto out;
+    }
 
     if (options[0])
         freq = get_nonzero_guint32(options[0], "802.11 channel frequency");
@@ -4484,12 +4495,6 @@ set_80211_channel(const char *iface, const char *opt)
     if (args >= 3 && options[3])
         center_freq2 = get_nonzero_guint32(options[3], "VHT center frequency 2");
 
-    ret = ws80211_init();
-    if (ret) {
-        cmdarg_err("%d: Failed to init ws80211: %s\n", abs(ret), g_strerror(abs(ret)));
-        ret = 2;
-        goto out;
-    }
     ret = ws80211_set_freq(iface, freq, type, center_freq1, center_freq2);
 
     if (ret) {

ui/qt/wireless_frame.cpp

@@ -50,7 +50,7 @@ WirelessFrame::WirelessFrame(QWidget *parent) :
 
     ui->helperToolButton->hide();
 
-    if (ws80211_init() == 0) {
+    if (ws80211_init() == WS80211_INIT_OK) {
         ui->stackedWidget->setEnabled(true);
         ui->stackedWidget->setCurrentWidget(ui->interfacePage);