From: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Date: Tue, 31 May 2022 01:41:31 +0000 (+0900)
Subject: seq: user_client: rewrite public API to return gboolean according to GNOME convention
X-Git-Url: https://git.alsa-project.org/?a=commitdiff_plain;h=899a718817d1cceff3bb370a038c350872ad8012;p=alsa-gobject.git

seq: user_client: rewrite public API to return gboolean according to GNOME convention

In GNOME convention, the throw function to report error at GError argument
should return gboolean value to report the overall operation finishes
successfully or not.

This commit rewrite such public APIs with loss of backward compatibility.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
---

diff --git a/samples/seq b/samples/seq
index 40802b4..c5f3db4 100755
--- a/samples/seq
+++ b/samples/seq
@@ -18,7 +18,7 @@ info.set_property('name', 'focal')
 client.set_info(info)
 
 # Dump client information.
-info = client.get_info(info)
+_, info = client.get_info(info)
 print('The information of client:')
 print('  type: {}'.format(info.get_property('type').value_nick))
 print('  filter-attributes: {}'.format(info.get_property('filter-attributes').value_nicks))
@@ -39,7 +39,7 @@ attrs = (ALSASeq.PortAttrFlag.MIDI_GENERIC |
          ALSASeq.PortAttrFlag.SOFTWARE |
          ALSASeq.PortAttrFlag.APPLICATION)
 info.set_property('attrs', attrs)
-info = client.create_port(info)
+_, info = client.create_port(info)
 
 # Dump port information.
 print('The information of port:')
@@ -57,7 +57,7 @@ info = ALSASeq.QueueInfo.new()
 info.set_property('name', '20.04')
 info.set_property('client-id', client.get_property('client-id'))
 info.set_property('locked', True)
-info = client.create_queue(info)
+_, info = client.create_queue(info)
 
 # Dump queue information.
 print('The information of queue:')
@@ -119,7 +119,7 @@ client.connect('handle-event', handle_event)
 
 # Create event dispatcher.
 dispatcher = GLib.MainLoop.new(None, False)
-src = client.create_source()
+_, src = client.create_source()
 src.attach(dispatcher.get_context())
 
 # Register UNIX signal handler.
diff --git a/src/seq/alsaseq.map b/src/seq/alsaseq.map
index 042963a..01a0df2 100644
--- a/src/seq/alsaseq.map
+++ b/src/seq/alsaseq.map
@@ -27,28 +27,6 @@ ALSA_GOBJECT_0_0_0 {
 
     "alsaseq_user_client_get_type";
     "alsaseq_user_client_new";
-    "alsaseq_user_client_open";
-    "alsaseq_user_client_get_protocol_version";
-    "alsaseq_user_client_set_info";
-    "alsaseq_user_client_get_info";
-    "alsaseq_user_client_create_port";
-    "alsaseq_user_client_create_port_at";
-    "alsaseq_user_client_update_port";
-    "alsaseq_user_client_delete_port";
-    "alsaseq_user_client_set_pool";
-    "alsaseq_user_client_get_pool";
-    "alsaseq_user_client_schedule_event";
-    "alsaseq_user_client_create_source";
-    "alsaseq_user_client_operate_subscription";
-    "alsaseq_user_client_create_queue";
-    "alsaseq_user_client_delete_queue";
-    "alsaseq_user_client_update_queue";
-    "alsaseq_user_client_get_queue_usage";
-    "alsaseq_user_client_set_queue_usage";
-    "alsaseq_user_client_set_queue_tempo";
-    "alsaseq_user_client_get_queue_tempo";
-    "alsaseq_user_client_set_queue_timer";
-    "alsaseq_user_client_get_queue_timer";
 
     "alsaseq_addr_get_type";
     "alsaseq_addr_new";
@@ -221,4 +199,27 @@ ALSA_GOBJECT_0_3_0 {
     "alsaseq_get_queue_info_by_id";
     "alsaseq_get_queue_info_by_name";
     "alsaseq_get_queue_status";
+
+    "alsaseq_user_client_open";
+    "alsaseq_user_client_get_protocol_version";
+    "alsaseq_user_client_set_info";
+    "alsaseq_user_client_get_info";
+    "alsaseq_user_client_create_port";
+    "alsaseq_user_client_create_port_at";
+    "alsaseq_user_client_update_port";
+    "alsaseq_user_client_delete_port";
+    "alsaseq_user_client_set_pool";
+    "alsaseq_user_client_get_pool";
+    "alsaseq_user_client_schedule_event";
+    "alsaseq_user_client_create_source";
+    "alsaseq_user_client_operate_subscription";
+    "alsaseq_user_client_create_queue";
+    "alsaseq_user_client_delete_queue";
+    "alsaseq_user_client_update_queue";
+    "alsaseq_user_client_get_queue_usage";
+    "alsaseq_user_client_set_queue_usage";
+    "alsaseq_user_client_set_queue_tempo";
+    "alsaseq_user_client_get_queue_tempo";
+    "alsaseq_user_client_set_queue_timer";
+    "alsaseq_user_client_get_queue_timer";
 } ALSA_GOBJECT_0_2_0;
diff --git a/src/seq/user-client.c b/src/seq/user-client.c
index 9d2f8fe..f59dab1 100644
--- a/src/seq/user-client.c
+++ b/src/seq/user-client.c
@@ -173,21 +173,22 @@ ALSASeqUserClient *alsaseq_user_client_new()
  *
  * The call of function executes `open(2)` system call, then executes `ioctl(2)` system call with
  * `SNDRV_SEQ_IOCTL_CLIENT_ID` command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag,
-                              GError **error)
+gboolean alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     char *devnode;
     int proto_ver;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     if (!alsaseq_get_seq_devnode(&devnode, error))
-        return;
+        return FALSE;
 
     open_flag |= O_RDWR;
     priv->fd = open(devnode, open_flag);
@@ -200,7 +201,7 @@ void alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag,
             generate_syscall_error(error, errno, "open(%s)", devnode);
 
         g_free(devnode);
-        return;
+        return FALSE;
     }
     priv->devnode = devnode;
 
@@ -208,6 +209,7 @@ void alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag,
         generate_syscall_error(error, errno, "ioctl(%s)", "CLIENT_ID");
         close(priv->fd);
         priv->fd = -1;
+        return FALSE;
     }
 
     // Remember the version of protocol currently used.
@@ -215,12 +217,14 @@ void alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag,
         generate_syscall_error(error, errno, "ioctl(%s)", "PVERSION");
         close(priv->fd);
         priv->fd = -1;
-        return;
+        return FALSE;
     }
 
     priv->proto_ver_triplet[0] = SNDRV_PROTOCOL_MAJOR(proto_ver);
     priv->proto_ver_triplet[1] = SNDRV_PROTOCOL_MINOR(proto_ver);
     priv->proto_ver_triplet[2] = SNDRV_PROTOCOL_MICRO(proto_ver);
+
+    return TRUE;
 }
 
 /**
@@ -233,21 +237,25 @@ void alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag,
  * Get the version of sequencer protocol currently used. The version is represented as the array
  * with three elements; major, minor, and micro version in the order. The length of major version
  * is 16 bit, the length of minor and micro version is 8 bit each.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_get_protocol_version(ALSASeqUserClient *self,
-                                        const guint16 *proto_ver_triplet[3],
-                                        GError **error)
+gboolean alsaseq_user_client_get_protocol_version(ALSASeqUserClient *self,
+                                                  const guint16 *proto_ver_triplet[3],
+                                                  GError **error)
 {
     ALSASeqUserClientPrivate *priv;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
-    g_return_if_fail(priv->fd >= 0);
+    g_return_val_if_fail(priv->fd >= 0, FALSE);
 
-    g_return_if_fail(proto_ver_triplet != NULL);
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(proto_ver_triplet != NULL, FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     *proto_ver_triplet = (const guint16 *)priv->proto_ver_triplet;
+
+    return TRUE;
 }
 
 /**
@@ -260,25 +268,30 @@ void alsaseq_user_client_get_protocol_version(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_CLIENT_INFO`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_set_info(ALSASeqUserClient *self,
-                                  ALSASeqClientInfo *client_info,
-                                  GError **error)
+gboolean alsaseq_user_client_set_info(ALSASeqUserClient *self, ALSASeqClientInfo *client_info,
+                                      GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_client_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_CLIENT_INFO(client_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_CLIENT_INFO(client_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_client_info_refer_private(client_info, &info);
     info->client = priv->client_id;
     info->type = USER_CLIENT;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_CLIENT_INFO, info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_CLIENT_INFO, info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "SET_CLIENT_INFO");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -291,25 +304,30 @@ void alsaseq_user_client_set_info(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_GET_CLIENT_INFO`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_get_info(ALSASeqUserClient *self,
-                                  ALSASeqClientInfo *const *client_info,
-                                  GError **error)
+gboolean alsaseq_user_client_get_info(ALSASeqUserClient *self,
+                                      ALSASeqClientInfo *const *client_info, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_client_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(client_info != NULL);
-    g_return_if_fail(ALSASEQ_IS_CLIENT_INFO(*client_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(client_info != NULL, FALSE);
+    g_return_val_if_fail(ALSASEQ_IS_CLIENT_INFO(*client_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_client_info_refer_private(*client_info, &info);
     info->client = priv->client_id;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_CLIENT_INFO, info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_CLIENT_INFO, info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "GET_CLIENT_INFO");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -322,25 +340,30 @@ void alsaseq_user_client_get_info(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_CREATE_PORT` command
  * for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_create_port(ALSASeqUserClient *self,
-                                     ALSASeqPortInfo *const *port_info,
-                                     GError **error)
+gboolean alsaseq_user_client_create_port(ALSASeqUserClient *self,
+                                         ALSASeqPortInfo *const *port_info, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_port_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_PORT_INFO(*port_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_PORT_INFO(*port_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_port_info_refer_private(*port_info, &info);
 
     info->addr.client = priv->client_id;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_CREATE_PORT, info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_CREATE_PORT, info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "CREATE_PORT");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -354,23 +377,25 @@ void alsaseq_user_client_create_port(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_CREATE_PORT` command
  * for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_create_port_at(ALSASeqUserClient *self,
-                                        ALSASeqPortInfo *const *port_info,
-                                        guint8 port_id, GError **error)
+gboolean alsaseq_user_client_create_port_at(ALSASeqUserClient *self,
+                                            ALSASeqPortInfo *const *port_info,
+                                            guint8 port_id, GError **error)
 {
     struct snd_seq_port_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
-    g_return_if_fail(ALSASEQ_IS_PORT_INFO(*port_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
+    g_return_val_if_fail(ALSASEQ_IS_PORT_INFO(*port_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_port_info_refer_private(*port_info, &info);
 
     info->addr.port = port_id;
     info->flags |= SNDRV_SEQ_PORT_FLG_GIVEN_PORT;
 
-    alsaseq_user_client_create_port(self, port_info, error);
+    return alsaseq_user_client_create_port(self, port_info, error);
 }
 
 /**
@@ -384,27 +409,32 @@ void alsaseq_user_client_create_port_at(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_PORT_INFO` command
  * for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_update_port(ALSASeqUserClient *self,
-                                     ALSASeqPortInfo *port_info,
-                                     guint8 port_id, GError **error)
+gboolean alsaseq_user_client_update_port(ALSASeqUserClient *self, ALSASeqPortInfo *port_info,
+                                         guint8 port_id, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_port_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_PORT_INFO(port_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_PORT_INFO(port_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_port_info_refer_private(port_info, &info);
 
     info->addr.client = priv->client_id;
     info->addr.port = port_id;
 
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_PORT_INFO, info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_PORT_INFO, info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "SET_PORT_INFO");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -417,22 +447,27 @@ void alsaseq_user_client_update_port(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_DELETE_PORT` command
  * for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_delete_port(ALSASeqUserClient *self,
-                                     guint8 port_id, GError **error)
+gboolean alsaseq_user_client_delete_port(ALSASeqUserClient *self, guint8 port_id, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_port_info info = {0};
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     info.addr.client = priv->client_id;
     info.addr.port = port_id;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_DELETE_PORT, &info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_DELETE_PORT, &info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "DELETE_PORT");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -445,24 +480,29 @@ void alsaseq_user_client_delete_port(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_CLIENT_POOL`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_set_pool(ALSASeqUserClient *self,
-                                  ALSASeqClientPool *client_pool,
-                                  GError **error)
+gboolean alsaseq_user_client_set_pool(ALSASeqUserClient *self, ALSASeqClientPool *client_pool,
+                                      GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_client_pool *pool;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_CLIENT_POOL(client_pool));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_CLIENT_POOL(client_pool), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_client_pool_refer_private(client_pool, &pool);
     pool->client = priv->client_id;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_CLIENT_POOL, pool) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_CLIENT_POOL, pool) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "SET_CLIENT_POOL");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -475,24 +515,29 @@ void alsaseq_user_client_set_pool(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_GET_CLIENT_POOL`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_get_pool(ALSASeqUserClient *self,
-                                  ALSASeqClientPool *const *client_pool,
-                                  GError **error)
+gboolean alsaseq_user_client_get_pool(ALSASeqUserClient *self,
+                                      ALSASeqClientPool *const *client_pool, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_client_pool *pool;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_CLIENT_POOL(*client_pool));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_CLIENT_POOL(*client_pool), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_client_pool_refer_private(*client_pool, &pool);
     pool->client = priv->client_id;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_CLIENT_POOL, pool) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_CLIENT_POOL, pool) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "GET_CLIENT_POOL");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -506,10 +551,11 @@ void alsaseq_user_client_get_pool(ALSASeqUserClient *self,
  * Deliver the event immediately, or schedule it into memory pool of the client.
  *
  * The call of function executes `write(2)` system call for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_schedule_event(ALSASeqUserClient *self,
-                                        ALSASeqEventCntr *ev_cntr,
-                                        gsize count, GError **error)
+gboolean alsaseq_user_client_schedule_event(ALSASeqUserClient *self, ALSASeqEventCntr *ev_cntr,
+                                            gsize count, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     gsize total;
@@ -517,17 +563,17 @@ void alsaseq_user_client_schedule_event(ALSASeqUserClient *self,
     gsize length;
     ssize_t len;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_EVENT_CNTR(ev_cntr));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_EVENT_CNTR(ev_cntr), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     alsaseq_event_cntr_count_events(ev_cntr, &total);
-    g_return_if_fail(count <= total);
+    g_return_val_if_fail(count <= total, FALSE);
 
     seq_event_cntr_get_buf(ev_cntr, count, &buf, &length);
-    g_return_if_fail(buf != NULL && length > 0);
+    g_return_val_if_fail(buf != NULL && length > 0, FALSE);
 
     len = write(priv->fd, buf, length);
     if (len < 0) {
@@ -537,7 +583,11 @@ void alsaseq_user_client_schedule_event(ALSASeqUserClient *self,
             generate_file_error(error, code, "write(%s)", priv->devnode);
         else
             generate_syscall_error(error, errno, "write(%s)", priv->devnode);
+
+        return FALSE;
     }
+
+    return TRUE;
 }
 
 static gboolean seq_user_client_check_src(GSource *gsrc)
@@ -606,9 +656,10 @@ static void seq_user_client_finalize_src(GSource *gsrc)
  * iteration of [struct@GLib.MainContext], the `read(2)` system call is exected to dispatch
  * sequencer event for [signal@UserClient::handle-event] signal, according to the result of
  * `poll(2)` system call.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_create_source(ALSASeqUserClient *self,
-                                       GSource **gsrc, GError **error)
+gboolean alsaseq_user_client_create_source(ALSASeqUserClient *self, GSource **gsrc, GError **error)
 {
     static GSourceFuncs funcs = {
             .check          = seq_user_client_check_src,
@@ -620,12 +671,12 @@ void alsaseq_user_client_create_source(ALSASeqUserClient *self,
     void *buf;
     long page_size = sysconf(_SC_PAGESIZE);
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
-    g_return_if_fail(priv->fd >= 0);
+    g_return_val_if_fail(priv->fd >= 0, FALSE);
 
-    g_return_if_fail(gsrc != NULL);
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(gsrc != NULL, FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     buf = g_malloc0(page_size);
 
@@ -642,6 +693,8 @@ void alsaseq_user_client_create_source(ALSASeqUserClient *self,
     src->tag = g_source_add_unix_fd(*gsrc, priv->fd, G_IO_IN);
     src->buf = buf;
     src->buf_len = page_size;
+
+    return TRUE;
 }
 
 /**
@@ -655,22 +708,23 @@ void alsaseq_user_client_create_source(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SUBSCRIBE_PORT` and
  * `SNDRV_SEQ_IOCTL_UNSUBSCRIBE_PORT` commands for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_operate_subscription(ALSASeqUserClient *self,
-                                         ALSASeqSubscribeData *subs_data,
-                                         gboolean establish,
-                                         GError **error)
+gboolean alsaseq_user_client_operate_subscription(ALSASeqUserClient *self,
+                                                  ALSASeqSubscribeData *subs_data,
+                                                  gboolean establish, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_port_subscribe *data;
     long request;
     const char *label;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_SUBSCRIBE_DATA(subs_data));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_SUBSCRIBE_DATA(subs_data), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_subscribe_data_refer_private(subs_data, &data);
 
@@ -687,7 +741,10 @@ void alsaseq_user_client_operate_subscription(ALSASeqUserClient *self,
             generate_local_error(error, ALSASEQ_USER_CLIENT_ERROR_PORT_PERMISSION);
         else
             generate_syscall_error(error, errno, "ioctl(%s)", label);
+        return FALSE;
     }
+
+    return TRUE;
 }
 
 /**
@@ -700,24 +757,29 @@ void alsaseq_user_client_operate_subscription(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_CREATE_QUEUE` command
  * for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_create_queue(ALSASeqUserClient *self,
-                                      ALSASeqQueueInfo *const *queue_info,
-                                      GError **error)
+gboolean alsaseq_user_client_create_queue(ALSASeqUserClient *self,
+                                          ALSASeqQueueInfo *const *queue_info, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_QUEUE_INFO(*queue_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_QUEUE_INFO(*queue_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_queue_info_refer_private(*queue_info, &info);
 
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_CREATE_QUEUE, info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_CREATE_QUEUE, info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "CREATE_QUEUE");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -730,22 +792,27 @@ void alsaseq_user_client_create_queue(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_DELETE_QUEUE` command
  * for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_delete_queue(ALSASeqUserClient *self,
-                                      guint8 queue_id, GError **error)
+gboolean alsaseq_user_client_delete_queue(ALSASeqUserClient *self, guint8 queue_id, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_info info = {0};
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     info.queue = (int)queue_id;
     info.owner = priv->client_id;
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_DELETE_QUEUE, &info) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_DELETE_QUEUE, &info) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "DELETE_QUEUE");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -758,19 +825,20 @@ void alsaseq_user_client_delete_queue(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_QUEUE_INFO`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_update_queue(ALSASeqUserClient *self,
-                                      ALSASeqQueueInfo *queue_info,
-                                      GError **error)
+gboolean alsaseq_user_client_update_queue(ALSASeqUserClient *self, ALSASeqQueueInfo *queue_info,
+                                          GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_info *info;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_QUEUE_INFO(queue_info));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_QUEUE_INFO(queue_info), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_queue_info_refer_private(queue_info, &info);
 
@@ -779,7 +847,10 @@ void alsaseq_user_client_update_queue(ALSASeqUserClient *self,
             generate_local_error(error, ALSASEQ_USER_CLIENT_ERROR_QUEUE_PERMISSION);
         else
             generate_syscall_error(error, errno, "ioctl(%s)", "SET_QUEUE_INFO");
+        return FALSE;
     }
+
+    return TRUE;
 }
 
 /**
@@ -793,27 +864,29 @@ void alsaseq_user_client_update_queue(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_GET_QUEUE_CLIENT`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_get_queue_usage(ALSASeqUserClient *self,
-                                         guint8 queue_id, gboolean *use,
-                                         GError **error)
+gboolean alsaseq_user_client_get_queue_usage(ALSASeqUserClient *self, guint8 queue_id,
+                                             gboolean *use, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_client data = {0};
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(use != NULL);
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(use != NULL, FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     data.queue = (int)queue_id;
     if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_QUEUE_CLIENT, &data) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "GET_QUEUE_CLIENT");
-        return;
+        return FALSE;
     }
 
     *use = data.used;
+    return TRUE;
 }
 
 /**
@@ -827,25 +900,30 @@ void alsaseq_user_client_get_queue_usage(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_QUEUE_CLIENT`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_set_queue_usage(ALSASeqUserClient *self,
-                                         guint8 queue_id, gboolean use,
-                                         GError **error)
+gboolean alsaseq_user_client_set_queue_usage(ALSASeqUserClient *self, guint8 queue_id,
+                                             gboolean use, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_client data = {0};
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     data.queue = (int)queue_id;
     data.client = priv->client_id;
     data.used = use;
 
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_QUEUE_CLIENT, &data) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_SET_QUEUE_CLIENT, &data) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "SET_QUEUE_CLIENT");
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /**
@@ -859,19 +937,20 @@ void alsaseq_user_client_set_queue_usage(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_QUEUE_TEMPO`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_set_queue_tempo(ALSASeqUserClient *self,
-                                guint8 queue_id, ALSASeqQueueTempo *queue_tempo,
-                                GError **error)
+gboolean alsaseq_user_client_set_queue_tempo(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTempo *queue_tempo, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_tempo *tempo;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_QUEUE_TEMPO(queue_tempo));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_QUEUE_TEMPO(queue_tempo), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_queue_tempo_refer_private(queue_tempo, &tempo);
     tempo->queue = queue_id;
@@ -880,7 +959,10 @@ void alsaseq_user_client_set_queue_tempo(ALSASeqUserClient *self,
             generate_local_error(error, ALSASEQ_USER_CLIENT_ERROR_QUEUE_PERMISSION);
         else
             generate_syscall_error(error, errno, "ioctl(%s)", "SET_QUEUE_TEMPO");
+        return FALSE;
     }
+
+    return TRUE;
 }
 
 /**
@@ -894,19 +976,20 @@ void alsaseq_user_client_set_queue_tempo(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_GET_QUEUE_TEMPO`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_get_queue_tempo(ALSASeqUserClient *self,
-                                guint8 queue_id, ALSASeqQueueTempo **queue_tempo,
-                                GError **error)
+gboolean alsaseq_user_client_get_queue_tempo(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTempo **queue_tempo, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_tempo *tempo;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(queue_tempo != NULL);
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(queue_tempo != NULL, FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     *queue_tempo = g_object_new(ALSASEQ_TYPE_QUEUE_TEMPO, NULL);
     seq_queue_tempo_refer_private(*queue_tempo, &tempo);
@@ -915,7 +998,10 @@ void alsaseq_user_client_get_queue_tempo(ALSASeqUserClient *self,
     if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_QUEUE_TEMPO, tempo) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "GET_QUEUE_TEMPO");
         g_object_unref(*queue_tempo);
+        return FALSE;
     }
+
+    return TRUE;
 }
 
 /**
@@ -929,20 +1015,20 @@ void alsaseq_user_client_get_queue_tempo(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_SET_QUEUE_TIMER`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self,
-                                         guint8 queue_id,
-                                         ALSASeqQueueTimer *queue_timer,
-                                         GError **error)
+gboolean alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTimer *queue_timer, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_timer *timer;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(ALSASEQ_IS_QUEUE_TIMER(queue_timer));
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(ALSASEQ_IS_QUEUE_TIMER(queue_timer), FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     seq_queue_timer_refer_private(queue_timer, &timer);
 
@@ -952,7 +1038,7 @@ void alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self,
     case SNDRV_SEQ_TIMER_MIDI_CLOCK:
     case SNDRV_SEQ_TIMER_MIDI_TICK:
     default:
-        g_return_if_reached();
+        g_return_val_if_reached(FALSE);
     }
 
     timer->queue = queue_id;
@@ -961,7 +1047,10 @@ void alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self,
             generate_local_error(error, ALSASEQ_USER_CLIENT_ERROR_QUEUE_PERMISSION);
         else
             generate_syscall_error(error, errno, "ioctl(%s)", "SET_QUEUE_TIMER");
+        return FALSE;
     }
+
+    return TRUE;
 }
 
 /**
@@ -975,20 +1064,20 @@ void alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_GET_QUEUE_TIMER`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self,
-                                         guint8 queue_id,
-                                         ALSASeqQueueTimer **queue_timer,
-                                         GError **error)
+gboolean alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTimer **queue_timer, GError **error)
 {
     ALSASeqUserClientPrivate *priv;
     struct snd_seq_queue_timer *timer;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(queue_timer != NULL);
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(queue_timer != NULL, FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
     *queue_timer = g_object_new(ALSASEQ_TYPE_QUEUE_TIMER, NULL);
     seq_queue_timer_refer_private(*queue_timer, &timer);
@@ -996,7 +1085,7 @@ void alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self,
     timer->queue = queue_id;
     if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_GET_QUEUE_TIMER, timer) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "GET_QUEUE_TIMER");
-        return;
+        return FALSE;
     }
 
     switch (timer->type) {
@@ -1008,8 +1097,10 @@ void alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self,
         // Not available.
         g_object_unref(*queue_timer);
         *queue_timer = NULL;
-        g_return_if_reached();
+        g_return_val_if_reached(FALSE);
     }
+
+    return TRUE;
 }
 
 /**
@@ -1022,19 +1113,24 @@ void alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self,
  *
  * The call of function executes `ioctl(2)` system call with `SNDRV_SEQ_IOCTL_REMOVE_EVENTS`
  * command for ALSA sequencer character device.
+ *
+ * Returns: %TRUE when the overall operation finishes successfully, else %FALSE.
  */
-void alsaseq_user_client_remove_events(ALSASeqUserClient *self,
-                                       ALSASeqRemoveFilter *filter,
-                                       GError **error)
+gboolean alsaseq_user_client_remove_events(ALSASeqUserClient *self, ALSASeqRemoveFilter *filter,
+                                           GError **error)
 {
     ALSASeqUserClientPrivate *priv;
 
-    g_return_if_fail(ALSASEQ_IS_USER_CLIENT(self));
+    g_return_val_if_fail(ALSASEQ_IS_USER_CLIENT(self), FALSE);
     priv = alsaseq_user_client_get_instance_private(self);
 
-    g_return_if_fail(filter != NULL);
-    g_return_if_fail(error == NULL || *error == NULL);
+    g_return_val_if_fail(filter != NULL, FALSE);
+    g_return_val_if_fail(error == NULL || *error == NULL, FALSE);
 
-    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_REMOVE_EVENTS, filter) < 0)
+    if (ioctl(priv->fd, SNDRV_SEQ_IOCTL_REMOVE_EVENTS, filter) < 0) {
         generate_syscall_error(error, errno, "ioctl(%s)", "REMOVE_EVENTS");
+        return FALSE;
+    }
+
+    return TRUE;
 }
diff --git a/src/seq/user-client.h b/src/seq/user-client.h
index 2a9c05a..386141f 100644
--- a/src/seq/user-client.h
+++ b/src/seq/user-client.h
@@ -34,88 +34,66 @@ struct _ALSASeqUserClientClass {
 
 ALSASeqUserClient *alsaseq_user_client_new();
 
-void alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag,
-                              GError **error);
-
-void alsaseq_user_client_get_protocol_version(ALSASeqUserClient *self,
-                                        const guint16 *proto_ver_triplet[3],
-                                        GError **error);
-
-void alsaseq_user_client_set_info(ALSASeqUserClient *self,
-                                  ALSASeqClientInfo *client_info,
-                                  GError **error);
-void alsaseq_user_client_get_info(ALSASeqUserClient *self,
-                                  ALSASeqClientInfo *const *client_info,
-                                  GError **error);
-
-void alsaseq_user_client_create_port(ALSASeqUserClient *self,
-                                     ALSASeqPortInfo *const *port_info,
-                                     GError **error);
-void alsaseq_user_client_create_port_at(ALSASeqUserClient *self,
-                                        ALSASeqPortInfo *const *port_info,
-                                        guint8 port_id, GError **error);
-
-void alsaseq_user_client_update_port(ALSASeqUserClient *self,
-                                     ALSASeqPortInfo *port_info,
-                                     guint8 port_id, GError **error);
-
-void alsaseq_user_client_delete_port(ALSASeqUserClient *self,
-                                     guint8 port_id, GError **error);
-
-void alsaseq_user_client_set_pool(ALSASeqUserClient *self,
-                                  ALSASeqClientPool *client_pool,
-                                  GError **error);
-
-void alsaseq_user_client_get_pool(ALSASeqUserClient *self,
-                                  ALSASeqClientPool *const *client_pool,
-                                  GError **error);
-
-void alsaseq_user_client_schedule_event(ALSASeqUserClient *self,
-                                        ALSASeqEventCntr *ev_cntr,
-                                        gsize count, GError **error);
-
-void alsaseq_user_client_create_source(ALSASeqUserClient *self,
-                                       GSource **gsrc, GError **error);
-
-void alsaseq_user_client_operate_subscription(ALSASeqUserClient *self,
-                                              ALSASeqSubscribeData *subs_data,
-                                              gboolean establish,
-                                              GError **error);
-
-void alsaseq_user_client_create_queue(ALSASeqUserClient *self,
-                                      ALSASeqQueueInfo *const *queue_info,
+gboolean alsaseq_user_client_open(ALSASeqUserClient *self, gint open_flag, GError **error);
+
+gboolean alsaseq_user_client_get_protocol_version(ALSASeqUserClient *self,
+                                                  const guint16 *proto_ver_triplet[3],
+                                                  GError **error);
+
+gboolean alsaseq_user_client_set_info(ALSASeqUserClient *self, ALSASeqClientInfo *client_info,
+                                      GError **error);
+gboolean alsaseq_user_client_get_info(ALSASeqUserClient *self,
+                                      ALSASeqClientInfo *const *client_info, GError **error);
+
+gboolean alsaseq_user_client_create_port(ALSASeqUserClient *self,
+                                         ALSASeqPortInfo *const *port_info, GError **error);
+gboolean alsaseq_user_client_create_port_at(ALSASeqUserClient *self,
+                                            ALSASeqPortInfo *const *port_info,
+                                            guint8 port_id, GError **error);
+
+gboolean alsaseq_user_client_update_port(ALSASeqUserClient *self, ALSASeqPortInfo *port_info,
+                                         guint8 port_id, GError **error);
+
+gboolean alsaseq_user_client_delete_port(ALSASeqUserClient *self, guint8 port_id, GError **error);
+
+gboolean alsaseq_user_client_set_pool(ALSASeqUserClient *self, ALSASeqClientPool *client_pool,
                                       GError **error);
-void alsaseq_user_client_delete_queue(ALSASeqUserClient *self,
-                                      guint8 queue_id, GError **error);
-void alsaseq_user_client_update_queue(ALSASeqUserClient *self,
-                                ALSASeqQueueInfo *queue_info, GError **error);
-
-void alsaseq_user_client_get_queue_usage(ALSASeqUserClient *self,
-                                         guint8 queue_id, gboolean *use,
-                                         GError **error);
-void alsaseq_user_client_set_queue_usage(ALSASeqUserClient *self,
-                                         guint8 queue_id, gboolean use,
-                                         GError **error);
-
-void alsaseq_user_client_set_queue_tempo(ALSASeqUserClient *self,
-                                guint8 queue_id, ALSASeqQueueTempo *queue_tempo,
-                                GError **error);
-void alsaseq_user_client_get_queue_tempo(ALSASeqUserClient *self,
-                                guint8 queue_id, ALSASeqQueueTempo **queue_tempo,
-                                GError **error);
-
-void alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self,
-                                         guint8 queue_id,
-                                         ALSASeqQueueTimer *queue_timer,
-                                         GError **error);
-void alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self,
-                                         guint8 queue_id,
-                                         ALSASeqQueueTimer **queue_timer,
-                                         GError **error);
-
-void alsaseq_user_client_remove_events(ALSASeqUserClient *self,
-                                       ALSASeqRemoveFilter *filter,
-                                       GError **error);
+
+gboolean alsaseq_user_client_get_pool(ALSASeqUserClient *self,
+                                      ALSASeqClientPool *const *client_pool, GError **error);
+
+gboolean alsaseq_user_client_schedule_event(ALSASeqUserClient *self, ALSASeqEventCntr *ev_cntr,
+                                            gsize count, GError **error);
+
+gboolean alsaseq_user_client_create_source(ALSASeqUserClient *self, GSource **gsrc, GError **error);
+
+gboolean alsaseq_user_client_operate_subscription(ALSASeqUserClient *self,
+                                                  ALSASeqSubscribeData *subs_data,
+                                                  gboolean establish, GError **error);
+
+gboolean alsaseq_user_client_create_queue(ALSASeqUserClient *self,
+                                          ALSASeqQueueInfo *const *queue_info, GError **error);
+gboolean alsaseq_user_client_delete_queue(ALSASeqUserClient *self, guint8 queue_id, GError **error);
+gboolean alsaseq_user_client_update_queue(ALSASeqUserClient *self, ALSASeqQueueInfo *queue_info,
+                                          GError **error);
+
+gboolean alsaseq_user_client_get_queue_usage(ALSASeqUserClient *self, guint8 queue_id,
+                                             gboolean *use, GError **error);
+gboolean alsaseq_user_client_set_queue_usage(ALSASeqUserClient *self, guint8 queue_id,
+                                             gboolean use, GError **error);
+
+gboolean alsaseq_user_client_set_queue_tempo(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTempo *queue_tempo, GError **error);
+gboolean alsaseq_user_client_get_queue_tempo(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTempo **queue_tempo, GError **error);
+
+gboolean alsaseq_user_client_set_queue_timer(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTimer *queue_timer, GError **error);
+gboolean alsaseq_user_client_get_queue_timer(ALSASeqUserClient *self, guint8 queue_id,
+                                             ALSASeqQueueTimer **queue_timer, GError **error);
+
+gboolean alsaseq_user_client_remove_events(ALSASeqUserClient *self, ALSASeqRemoveFilter *filter,
+                                           GError **error);
 
 G_END_DECLS