device: Add Doxygen comments, improve error handling.

- Add Doxygen comments for all functions (some TODOs remain).

 - Check return code of more functions, handle invalid input.

backend.c

@@ -38,7 +38,6 @@ int sr_init(void)
  */
 int sr_exit(void)
 {
-
 	sr_cleanup_hwplugins();
 
 	return SR_OK;

device.c

@@ -26,13 +26,47 @@ extern struct sr_global *global;
 
 GSList *devices = NULL;
 
-
+/**
+ * Scan the system for attached logic analyzers / devices.
+ *
+ * This will try to autodetect all supported logic analyzer devices:
+ *
+ *  - Those attached via USB (can be reliably detected via USB VID/PID).
+ *
+ *  - Those using a (real or virtual) serial port (detected by sending
+ *    device-specific commands to all OS-specific serial port devices such
+ *    as /dev/ttyS*, /dev/ttyUSB*, /dev/ttyACM*, and others).
+ *    The autodetection for this kind of devices can potentially be unreliable.
+ *
+ *    Also, sending various bytes/commands to (all!) devices which happen to
+ *    be attached to the system via a (real or virtual) serial port can be
+ *    problematic. There is no way for libsigrok to know how unknown devices
+ *    react to the bytes libsigrok sends. Potentially they could lead to the
+ *    device getting into invalid/error states, losing/overwriting data, or...
+ *
+ * In addition to the detection, the devices that are found are also
+ * initialized automatically. On some devices, this involves a firmware upload,
+ * or other such measures.
+ *
+ * The order in which the system is scanned for devices is not specified. The
+ * caller should not assume or rely on any specific order.
+ *
+ * After the system has been scanned for devices, the list of detected (and
+ * supported) devices can be acquired via sr_device_list().
+ *
+ * TODO: Should return int.
+ * TODO: Error checks?
+ * TODO: Option to only scan for specific devices or device classes.
+ */
 void sr_device_scan(void)
 {
 	GSList *plugins, *l;
 	struct sr_device_plugin *plugin;
 
-	plugins = sr_list_hwplugins();
+	if (!(plugins = sr_list_hwplugins())) {
+		sr_err("dev: %s: no supported devices/hwplugins", __func__);
+		return; /* TODO? */
+	}
 
 	/*
 	 * Initialize all plugins first. Since the init() call may involve
@@ -41,26 +75,62 @@ void sr_device_scan(void)
 	 */
 	for (l = plugins; l; l = l->next) {
 		plugin = l->data;
+		/* TODO: Handle 'plugin' being NULL. */
 		sr_init_hwplugins(plugin);
 	}
-
 }
 
+/**
+ * Return the list of logic analyzer devices libsigrok has detected.
+ *
+ * If the libsigrok-internal device list is empty, a scan for attached
+ * devices -- via a call to sr_device_scan() -- is performed first.
+ *
+ * TODO: Error handling?
+ *
+ * @return The list (GSList) of detected devices, or NULL if none were found.
+ */
 GSList *sr_device_list(void)
 {
-
 	if (!devices)
 		sr_device_scan();
 
 	return devices;
 }
 
+/**
+ * Create a new device.
+ *
+ * TODO: 'plugin' can be const.
+ * TODO: num_probes should be uint16_t.
+ * TODO: Should return int, so that we can return SR_OK, SR_ERR_* etc.
+ *
+ * It is the caller's responsibility to g_free() the allocated memory when
+ * no longer needed. TODO: Using which API function?
+ *
+ * @param plugin TODO.
+ *               If 'plugin' is NULL, the created device is a "virtual" one.
+ * @param plugin_index TODO
+ * @param num_probes The number of probes (>= 1) this device has.
+ *                   TODO: 0 allowed?
+ *
+ * @return Pointer to the newly allocated device, or NULL upon errors.
+ */
 struct sr_device *sr_device_new(struct sr_device_plugin *plugin, int plugin_index,
-			     int num_probes)
+			        int num_probes)
 {
 	struct sr_device *device;
 	int i;
 
+	if (!plugin) {
+		sr_err("dev: %s: plugin was NULL", __func__);
+		return NULL; /* TODO: SR_ERR_ARG */
+	}
+
+	/* TODO: Check if plugin_index valid? */
+
+	/* TODO: Check if num_probes valid? */
+
 	if (!(device = g_try_malloc0(sizeof(struct sr_device)))) {
 		sr_err("dev: %s: device malloc failed", __func__);
 		return NULL;
@@ -71,53 +141,134 @@ struct sr_device *sr_device_new(struct sr_device_plugin *plugin, int plugin_inde
 	devices = g_slist_append(devices, device);
 
 	for (i = 0; i < num_probes; i++)
-		sr_device_probe_add(device, NULL);
+		sr_device_probe_add(device, NULL); /* TODO: Check return value. */
 
 	return device;
 }
 
+/**
+ * Clear all probes of the specified device.
+ *
+ * This removes/clears the 'name' and 'trigger' fields of all probes of
+ * the device.
+ *
+ * The order in which the probes are cleared is not specified. The caller
+ * should not assume or rely on a specific order.
+ *
+ * TODO: Should return int.
+ * TODO: Rename to sr_device_clear_probes() or sr_device_probe_clear_all().
+ *
+ * @param device The device whose probes to clear. Must not be NULL.
+ *               Note: device->probes is allowed to be NULL (in that case,
+ *               there are no probes, thus none have to be cleared).
+ */
 void sr_device_clear(struct sr_device *device)
 {
 	unsigned int pnum;
 
-	if (!device->probes)
+	if (!device) {
-		return;
+		sr_err("dev: %s: device was NULL", __func__);
+		return; /* TODO: SR_ERR_ARG. */
+	}
+
+	/* Note: device->probes can be NULL, this is handled correctly. */
 
 	for (pnum = 1; pnum <= g_slist_length(device->probes); pnum++)
 		sr_device_probe_clear(device, pnum);
+
+	/* TODO: return SR_OK; */
 }
 
+/**
+ * Clear the specified probe in the specified device.
+ *
+ * The probe itself still exists afterwards, but its 'name' and 'trigger'
+ * fields are g_free()'d and set to NULL.
+ *
+ * TODO: Should return int.
+ *
+ * @param device The device in which the specified (to be cleared) probe
+ *               resides. Must not be NULL.
+ * @param probenum The number of the probe to clear.
+ *                 Note that the probe numbers start at 1 (not 0!).
+ */
 void sr_device_probe_clear(struct sr_device *device, int probenum)
 {
 	struct sr_probe *p;
 
-	p = sr_device_probe_find(device, probenum);
+	if (!device) {
-	if (!p)
+		sr_err("dev: %s: device was NULL", __func__);
-		return;
+		return; /* TODO: SR_ERR_ARG. */
+	}
 
+	/* TODO: Sanity check on 'probenum'. */
+
+	if (!(p = sr_device_probe_find(device, probenum))) {
+		sr_err("dev: %s: probe %d not found", __func__, probenum);
+		return; /* TODO: SR_ERR*. */
+	}
+
+	/* If the probe has a name, remove it. */
 	if (p->name) {
 		g_free(p->name);
 		p->name = NULL;
 	}
 
+	/* If the probe has a trigger, remove it. */
 	if (p->trigger) {
 		g_free(p->trigger);
 		p->trigger = NULL;
 	}
+
+	/* TODO: return SR_OK; */
 }
 
+/**
+ * Add a probe with the specified name to the specified device.
+ *
+ * The added probe is automatically enabled (the 'enabled' field is TRUE).
+ *
+ * The 'trigger' field of the added probe is set to NULL. A trigger can be
+ * added via sr_device_trigger_set().
+ *
+ * TODO: Should return int.
+ * TODO: Are duplicate names allowed?
+ * TODO: Do we enforce a maximum probe number for a device?
+ * TODO: Error if the max. probe number for the specific LA is reached, e.g.
+ *       if the caller tries to add more probes than the device actually has.
+ *
+ * @param device The device to which to add a probe with the specified name.
+ *               Must not be NULL.
+ * @param name The name of the probe to add to this device. Must not be NULL.
+ *             TODO: Maximum length, allowed characters, etc.
+ *
+ * @return SR_OK upon success, SR_ERR_MALLOC upon memory allocation errors,
+ *         or SR_ERR_ARG upon invalid arguments.
+ *         If something other than SR_OK is returned, 'device' is unchanged.
+ */
 void sr_device_probe_add(struct sr_device *device, const char *name)
 {
 	struct sr_probe *p;
-	char probename[16];
+	char probename[16]; /* FIXME: Don't hardcode 16? #define? */
 	int probenum;
 
+	if (!device) {
+		sr_err("dev: %s: device was NULL", __func__);
+		return; /* SR_ERR_ARG; */
+	}
+
+	if (!name) {
+		sr_err("dev: %s: name was NULL", __func__);
+		return; /* SR_ERR_ARG; */
+	}
+
+	/* TODO: Further checks to ensure name is valid. */
+
 	probenum = g_slist_length(device->probes) + 1;
 
 	if (!(p = g_try_malloc0(sizeof(struct sr_probe)))) {
 		sr_err("dev: %s: p malloc failed", __func__);
-		// return SR_ERR_MALLOC;
+		return; /* SR_ERR_MALLOC; */
-		return; /* FIXME: should return int. */
 	}
 
 	p->index = probenum;
@@ -130,16 +281,42 @@ void sr_device_probe_add(struct sr_device *device, const char *name)
 	}
 	p->trigger = NULL;
 	device->probes = g_slist_append(device->probes, p);
+
+	return SR_OK;
 }
 
+/**
+ * Find the probe with the specified number in the specified device.
+ *
+ * TODO
+ *
+ * @param device TODO. Must not be NULL.
+ * @param probenum The number of the probe whose 'struct sr_probe' we want.
+ *                 Note that the probe numbers start at 1 (not 0!).
+ *
+ * TODO: Should return int.
+ * TODO: device can be const.
+ * TODO: probenum should be unsigned.
+ *
+ * @return A pointer to the requested probe's 'struct sr_probe', or NULL
+ *         if the probe could not be found.
+ */
 struct sr_probe *sr_device_probe_find(struct sr_device *device, int probenum)
 {
 	GSList *l;
 	struct sr_probe *p, *found_probe;
 
+	if (!device) {
+		sr_err("dev: %s: device was NULL", __func__);
+		return NULL; /* TODO: SR_ERR_ARG */
+	}
+
+	/* TODO: Sanity check on probenum. */
+
 	found_probe = NULL;
 	for (l = device->probes; l; l = l->next) {
 		p = l->data;
+		/* TODO: Check for p != NULL. */
 		if (p->index == probenum) {
 			found_probe = p;
 			break;
@@ -149,32 +326,74 @@ struct sr_probe *sr_device_probe_find(struct sr_device *device, int probenum)
 	return found_probe;
 }
 
-/* TODO: return SR_ERR if probenum not found */
+/**
+ * Set the name of the specified probe in the specified device.
+ *
+ * If the probe already has a different name assigned to it, it will be
+ * removed, and the new name will be saved instead.
+ *
+ * TODO: Should return int.
+ * TODO: device can be const?
+ * TODO: Rename to sr_device_set_probe_name().
+ *
+ * @param device TODO
+ * @param probenum The number of the probe whose name to set.
+ *                 Note that the probe numbers start at 1 (not 0!).
+ * @param name The new name that the specified probe should get.
+ */
 void sr_device_probe_name(struct sr_device *device, int probenum,
 			  const char *name)
 {
 	struct sr_probe *p;
 
-	p = sr_device_probe_find(device, probenum);
+	if (!device) {
-	if (!p)
+		sr_err("dev: %s: device was NULL", __func__);
-		return;
+		return; /* TODO: SR_ERR_ARG */
+	}
 
+	p = sr_device_probe_find(device, probenum);
+	if (!p) {
+		sr_err("dev: %s: probe %d not found", __func__, probenum);
+		return; /* TODO: SR_ERR*. */
+	}
+
+	/* TODO: Sanity check on 'name'. */
+
+	/* If the probe already has a name, kill it first. */
 	if (p->name)
 		g_free(p->name);
+
 	p->name = g_strdup(name);
 }
 
-/* TODO: return SR_ERR if probenum not found */
+/**
+ * Remove all triggers set up for the specified device.
+ *
+ * TODO: Better description.
+ *
+ * TODO: Should return int.
+ * TODO: device can be const?
+ *
+ * @param device TODO
+ */
 void sr_device_trigger_clear(struct sr_device *device)
 {
 	struct sr_probe *p;
-	unsigned int pnum;
+	unsigned int pnum; /* TODO: uint6_t? */
 
-	if (!device->probes)
+	if (!device) {
-		return;
+		sr_err("dev: %s: device was NULL", __func__);
+		return; /* TODO: SR_ERR_ARG */
+	}
+
+	if (!device->probes) {
+		sr_err("dev: %s: device->probes was NULL", __func__);
+		return; /* TODO: SR_ERR*. */
+	}
 
 	for (pnum = 1; pnum <= g_slist_length(device->probes); pnum++) {
 		p = sr_device_probe_find(device, pnum);
+		/* TODO: Silently ignore probes which cannot be found? */
 		if (p && p->trigger) {
 			g_free(p->trigger);
 			p->trigger = NULL;
@@ -182,34 +401,92 @@ void sr_device_trigger_clear(struct sr_device *device)
 	}
 }
 
-/* TODO: return SR_ERR if probenum not found */
+/**
+ * Add a trigger to the specified device.
+ *
+ * TODO: Better description.
+ * TODO: Describe valid format of the 'trigger' string.
+ *
+ * TODO: Should return int.
+ * TODO: device can be const?
+ *
+ * @param device TODO. Must not be NULL.
+ * @param probenum The number of the probe. TODO.
+ *                 Note that the probe numbers start at 1 (not 0!).
+ * @param trigger TODO.
+ *                TODO: Is NULL allowed?
+ */
 void sr_device_trigger_set(struct sr_device *device, int probenum,
 			   const char *trigger)
 {
 	struct sr_probe *p;
 
-	p = sr_device_probe_find(device, probenum);
+	if (!device) {
-	if (!p)
+		sr_err("dev: %s: device was NULL", __func__);
-		return;
+		return; /* TODO: SR_ERR_ARG */
+	}
 
+	/* TODO: Sanity check on 'probenum'. */
+
+	/* TODO: Sanity check on 'trigger'. */
+
+	p = sr_device_probe_find(device, probenum);
+	if (!p) {
+		sr_err("dev: %s: probe %d not found", __func__, probenum);
+		return; /* TODO: SR_ERR*. */
+	}
+
+	/* If the probe already has a trigger, kill it first. */
 	if (p->trigger)
 		g_free(p->trigger);
 
 	p->trigger = g_strdup(trigger);
-
 }
 
+/**
+ * Determine whether the specified device has the specified capability.
+ *
+ * TODO: Should return int?
+ * TODO: device can be const.
+ *
+ * @param device Pointer to the device to be checked. Must not be NULL.
+ *               The device's 'plugin' field must not be NULL either.
+ * @param hwcap The capability that should be checked (whether it's supported
+ *              by the specified device).
+ *
+ * @return TRUE, if the device has the specified capability, FALSE otherwise.
+ *         FALSE is also returned upon invalid input parameters or other
+ *         error conditions.
+ */
 gboolean sr_device_has_hwcap(struct sr_device *device, int hwcap)
 {
 	int *capabilities, i;
 
-	if (!device || !device->plugin)
+	if (!device) {
-		return FALSE;
+		sr_err("dev: %s: device was NULL", __func__);
+		return FALSE; /* TODO: SR_ERR_ARG. */
+	}
 
-	if ((capabilities = device->plugin->get_capabilities()))
+	if (!device->plugin) {
-		for (i = 0; capabilities[i]; i++)
+		sr_err("dev: %s: device->plugin was NULL", __func__);
-			if (capabilities[i] == hwcap)
+		return FALSE; /* TODO: SR_ERR_ARG. */
-				return TRUE;
+	}
+
+	/* TODO: Sanity check on 'hwcap'. */
+
+	if (!(capabilities = device->plugin->get_capabilities())) {
+		sr_err("dev: %s: device has no capabilities", __func__);
+		return FALSE; /* TODO: SR_ERR*. */
+	}
+
+	for (i = 0; capabilities[i]; i++) {
+		if (capabilities[i] != hwcap)
+			continue;
+		sr_spew("dev: %s: found hwcap %d", __func__, hwcap);
+		return TRUE;
+	}
+
+	sr_spew("dev: %s: hwcap %d not found", __func__, hwcap);
 
 	return FALSE;
 }