Add snd_pcm_parse_control_id()

Added a new function snd_pcm_parse_control_id() for the user controls.
This can be used in external plugins, too.

src/pcm/pcm_misc.c

@@ -700,3 +700,146 @@ snd_pcm_format_t snd_pcm_build_linear_format(int width, int pwidth, int unsignd,
 		return ((int(*)[2][2])linear_formats)[width][!!unsignd][!!big_endian];
 	}
 }
+
+/**
+ * \brief Parse control element id from the config
+ * \param conf the config tree to parse
+ * \param ctl_id the pointer to store the resultant control element id
+ * \param cardp the pointer to store the card index
+ * \param cchannelsp the pointer to store the number of channels (optional)
+ * \param hwctlp the pointer to store the h/w control flag (optional)
+ * \return 0 if successful, or a negative error code
+ *
+ * This function parses the given config tree to retrieve the control element id
+ * and the card index.  It's used by softvol.  External PCM plugins can use this
+ * function for creating or assigining their controls.
+ *
+ * cchannelsp and hwctlp arguments are optional.  Set NULL if not necessary.
+ */
+int snd_pcm_parse_control_id(snd_config_t *conf, snd_ctl_elem_id_t *ctl_id, int *cardp,
+			     int *cchannelsp, int *hwctlp)
+{
+	snd_config_iterator_t i, next;
+	int iface = SND_CTL_ELEM_IFACE_MIXER;
+	const char *name = NULL;
+	long index = 0;
+	long device = -1;
+	long subdevice = -1;
+	int err;
+
+	assert(ctl_id && cardp);
+
+	*cardp = -1;
+	if (cchannelsp)
+		*cchannelsp = 2;
+	snd_config_for_each(i, next, conf) {
+		snd_config_t *n = snd_config_iterator_entry(i);
+		const char *id;
+		if (snd_config_get_id(n, &id) < 0)
+			continue;
+		if (strcmp(id, "comment") == 0)
+			continue;
+		if (strcmp(id, "card") == 0) {
+			const char *str;
+			long v;
+			if ((err = snd_config_get_integer(n, &v)) < 0) {
+				if ((err = snd_config_get_string(n, &str)) < 0) {
+					SNDERR("Invalid field %s", id);
+					goto _err;
+				}
+				*cardp = snd_card_get_index(str);
+				if (*cardp < 0) {
+					SNDERR("Cannot get index for %s", str);
+					err = *cardp;
+					goto _err;
+				}
+			} else
+				*cardp = v;
+			continue;
+		}
+		if (strcmp(id, "iface") == 0 || strcmp(id, "interface") == 0) {
+			const char *ptr;
+			if ((err = snd_config_get_string(n, &ptr)) < 0) {
+				SNDERR("field %s is not a string", id);
+				goto _err;
+			}
+			if ((err = snd_config_get_ctl_iface_ascii(ptr)) < 0) {
+				SNDERR("Invalid value for '%s'", id);
+				goto _err;
+			}
+			iface = err;
+			continue;
+		}
+		if (strcmp(id, "name") == 0) {
+			if ((err = snd_config_get_string(n, &name)) < 0) {
+				SNDERR("field %s is not a string", id);
+				goto _err;
+			}
+			continue;
+		}
+		if (strcmp(id, "index") == 0) {
+			if ((err = snd_config_get_integer(n, &index)) < 0) {
+				SNDERR("field %s is not an integer", id);
+				goto _err;
+			}
+			continue;
+		}
+		if (strcmp(id, "device") == 0) {
+			if ((err = snd_config_get_integer(n, &device)) < 0) {
+				SNDERR("field %s is not an integer", id);
+				goto _err;
+			}
+			continue;
+		}
+		if (strcmp(id, "subdevice") == 0) {
+			if ((err = snd_config_get_integer(n, &subdevice)) < 0) {
+				SNDERR("field %s is not an integer", id);
+				goto _err;
+			}
+			continue;
+		}
+		if (cchannelsp && strcmp(id, "count") == 0) {
+			long v;
+			if ((err = snd_config_get_integer(n, &v)) < 0) {
+				SNDERR("field %s is not an integer", id);
+				goto _err;
+			}
+			if (v < 1 || v > 2) {
+				SNDERR("Invalid count %ld", v);
+				goto _err;
+			}
+			*cchannelsp = v;
+			continue;
+		}
+		if (hwctlp && strcmp(id, "hwctl") == 0) {
+			if ((err = snd_config_get_bool(n)) < 0) {
+				SNDERR("The field %s must be a boolean type", id);
+				return err;
+			}
+			*hwctlp = err;
+			continue;
+		}
+		SNDERR("Unknown field %s", id);
+		return -EINVAL;
+	}
+	if (name == NULL) {
+		SNDERR("Missing control name");
+		err = -EINVAL;
+		goto _err;
+	}
+	if (device < 0)
+		device = 0;
+	if (subdevice < 0)
+		subdevice = 0;
+
+	snd_ctl_elem_id_set_interface(ctl_id, iface);
+	snd_ctl_elem_id_set_name(ctl_id, name);
+	snd_ctl_elem_id_set_index(ctl_id, index);
+	snd_ctl_elem_id_set_device(ctl_id, device);
+	snd_ctl_elem_id_set_subdevice(ctl_id, subdevice);
+
+	return 0;
+
+ _err:
+	return err;
+}