sr_driver_scan(): Improve checks.

Check the relevant arguments for != NULL before calling the actual
driver-specific function, so that the driver can safely assume those
arguments are non-NULL. This removes the need to duplicate these
checks in every driver.

Also, do some minor whitespace and consistency improvements.

hardware/asix-sigma/asix-sigma.c

@@ -448,7 +448,9 @@ static GSList *hw_scan(GSList *options)
 	(void)options;
 
 	drvc = di->priv;
+
 	devices = NULL;
+
 	clear_instances();
 
 	if (!(devc = g_try_malloc(sizeof(struct dev_context)))) {

hardware/chronovu-la8/api.c

@@ -96,6 +96,7 @@ static GSList *hw_scan(GSList *options)
 	(void)options;
 
 	drvc = di->priv;
+
 	devices = NULL;
 
 	/* Allocate memory for our private device context. */
@@ -169,8 +170,6 @@ static GSList *hw_scan(GSList *options)
 	devices = g_slist_append(devices, sdi);
 	drvc->instances = g_slist_append(drvc->instances, sdi);
 
-	sr_spew("Device init successful.");
-
 	/* Close device. We'll reopen it again when we need it. */
 	(void) la8_close(devc); /* Log, but ignore errors. */
 

hardware/colead-slm/api.c

@@ -97,10 +97,11 @@ static GSList *hw_scan(GSList *options)
 	GSList *devices, *l;
 	const char *conn, *serialcomm;
 
-	devices = NULL;
 	drvc = di->priv;
 	drvc->instances = NULL;
 
+	devices = NULL;
+
 	conn = serialcomm = NULL;
 	for (l = options; l; l = l->next) {
 		src = l->data;
@@ -123,7 +124,7 @@ static GSList *hw_scan(GSList *options)
 		return NULL;
 
 	if (!(devc = g_try_malloc0(sizeof(struct dev_context)))) {
-		sr_dbg("failed to malloc devc");
+		sr_dbg("Device context malloc failed.");
 		return NULL;
 	}
 

hardware/demo/demo.c

@@ -172,6 +172,7 @@ static GSList *hw_scan(GSList *options)
 	(void)options;
 
 	drvc = di->priv;
+
 	devices = NULL;
 
 	sdi = sr_dev_inst_new(0, SR_ST_ACTIVE, DEMONAME, NULL, NULL);

hardware/hantek-dso/api.c

@@ -285,11 +285,12 @@ static GSList *hw_scan(GSList *options)
 
 	(void)options;
 
-	devcnt = 0;
-	devices = 0;
 	drvc = di->priv;
 	drvc->instances = NULL;
 
+	devcnt = 0;
+	devices = 0;
+
 	clear_instances();
 
 	/* Find all Hantek DSO devices and upload firmware to all of them. */

hardware/lascar-el-usb/api.c

@@ -95,10 +95,7 @@ static GSList *hw_scan(GSList *options)
 
 	(void)options;
 
-	if (!(drvc = di->priv)) {
+	drvc = di->priv;
-		sr_err("Driver was not initialized.");
-		return NULL;
-	}
 
 	/* USB scan is always authoritative. */
 	clear_instances();

hardware/nexus-osciprime/api.c

@@ -167,10 +167,7 @@ static GSList *hw_scan(GSList *options)
 
 	(void)options;
 
-	if (!(drvc = di->priv)) {
+	drvc = di->priv;
-		sr_err("Driver was not initialized.");
-		return NULL;
-	}
 
 	/* USB scan is always authoritative. */
 	clear_instances();

hardware/openbench-logic-sniffer/api.c

@@ -85,7 +85,9 @@ static GSList *hw_scan(GSList *options)
 	char buf[8];
 
 	(void)options;
+
 	drvc = di->priv;
+
 	devices = NULL;
 
 	conn = serialcomm = NULL;

hardware/rigol-ds1xx2/api.c

@@ -188,10 +188,11 @@ static GSList *hw_scan(GSList *options)
 
 	(void)options;
 
-	devices = NULL;
 	drvc = di->priv;
 	drvc->instances = NULL;
 
+	devices = NULL;
+
 	dir = g_dir_open("/sys/class/usb/", 0, NULL);
 
 	if (dir == NULL)

hardware/tondaj-sl-814/api.c

@@ -93,10 +93,11 @@ static GSList *hw_scan(GSList *options)
 	GSList *devices, *l;
 	const char *conn, *serialcomm;
 
-	devices = NULL;
 	drvc = di->priv;
 	drvc->instances = NULL;
 
+	devices = NULL;
+
 	conn = serialcomm = NULL;
 	for (l = options; l; l = l->next) {
 		if (!(src = l->data)) {

hardware/victor-dmm/api.c

@@ -100,10 +100,7 @@ static GSList *hw_scan(GSList *options)
 
 	(void)options;
 
-	if (!(drvc = di->priv)) {
+	drvc = di->priv;
-		sr_err("Driver was not initialized.");
-		return NULL;
-	}
 
 	/* USB scan is always authoritative. */
 	clear_instances();

hardware/zeroplus-logic-cube/zeroplus.c

@@ -317,6 +317,7 @@ static GSList *hw_scan(GSList *options)
 	(void)options;
 
 	drvc = di->priv;
+
 	devices = NULL;
 
 	clear_instances();

hwdriver.c

@@ -289,21 +289,39 @@ SR_API int sr_driver_init(struct sr_context *ctx, struct sr_dev_driver *driver)
  * The order in which the system is scanned for devices is not specified. The
  * caller should not assume or rely on any specific order.
  *
- * @param driver The driver.
+ * Before calling sr_driver_scan(), the user must have previously initialized
- * @param options A list of struct sr_hwopt options to pass to the driver's
+ * the driver by calling sr_driver_init().
- * 		scanner.
  *
- * @return A GSList * of struct sr_dev_inst, or NULL if no devices were found.
+ * @param driver The driver that should scan. This must be a pointer to one of
- * This list must be freed by the caller, but without freeing the data
+ *               the entries returned by sr_driver_list(). Must not be NULL.
- * pointed to in the list.
+ * @param options A list of 'struct sr_hwopt' options to pass to the driver's
+ *                scanner. Can be NULL/empty.
+ *
+ * @return A GSList * of 'struct sr_dev_inst', or NULL if no devices were
+ *         found (or errors were encountered). This list must be freed by the
+ *         caller using g_slist_free(), but without freeing the data pointed
+ *         to in the list.
  */
 SR_API GSList *sr_driver_scan(struct sr_dev_driver *driver, GSList *options)
 {
+	GSList *l;
 
-	if (driver->scan)
+	if (!driver) {
-		return driver->scan(options);
+		sr_err("Invalid driver, can't scan for devices.");
+		return NULL;
+	}
 
-	return NULL;
+	if (!driver->priv) {
+		sr_err("Driver not initialized, can't scan for devices.");
+		return NULL;
+	}
+
+	l = driver->scan(options);
+
+	sr_spew("Scan of '%s' found %d devices.", driver->name,
+		g_slist_length(l));
+
+	return l;
 }
 
 /** @private */