The current ALSA sequencer core tries to register the new kernel
sequencer port on the list at first, then fill up the port
information.  This means that user-space may sneak the wrong
information before the actual data is filled, which isn't ideal.
Although the user-space should try to query the port info after the
port registration notification is sent out, it'd be still better to
have a port available with the full info from the beginning.

This patch changes the sequencer port creation and registration
procedure; now split to two steps, for creation and insertion, and the
port is registered after the information is filled.

Link: https://sashiko.dev/#/patchset/20260518194023.1667857-1-maoyixie.tju%40gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/seq/seq_clientmgr.c |  7 ++++++-
 sound/core/seq/seq_ports.c     | 24 ++++++++++++++++--------
 sound/core/seq/seq_ports.h     |  8 ++++++--
 3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 5719637575a9..19d6fea012f6 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1287,7 +1287,7 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client, void *arg)
 		port_idx = -1;
 	if (port_idx >= SNDRV_SEQ_ADDRESS_UNKNOWN)
 		return -EINVAL;
-	err = snd_seq_create_port(client, port_idx, &port);
+	err = snd_seq_create_port(client, &port);
 	if (err < 0)
 		return err;
 
@@ -1309,6 +1309,11 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client, void *arg)
 	info->addr = port->addr;
 
 	snd_seq_set_port_info(port, info);
+	err = snd_seq_insert_port(client, port_idx, port);
+	if (err < 0) {
+		kfree(port);
+		return err;
+	}
 	if (info->capability & SNDRV_SEQ_PORT_CAP_UMP_ENDPOINT)
 		client->ump_endpoint_port = port->addr.port;
 	snd_seq_system_client_ev_port_start(port->addr.client, port->addr.port);
diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
index 31ab4681c601..17daacd4476a 100644
--- a/sound/core/seq/seq_ports.c
+++ b/sound/core/seq/seq_ports.c
@@ -108,14 +108,13 @@ static void port_subs_info_init(struct snd_seq_port_subs_info *grp)
 }
 
 
-/* create a port, port number or a negative error code is returned
+/* create a port, 0 on success or a negative error code is returned
  * the caller needs to unref the port via snd_seq_port_unlock() appropriately
  */
-int snd_seq_create_port(struct snd_seq_client *client, int port,
+int snd_seq_create_port(struct snd_seq_client *client,
 			struct snd_seq_client_port **port_ret)
 {
-	struct snd_seq_client_port *new_port, *p;
-	int num;
+	struct snd_seq_client_port *new_port;
 	
 	*port_ret = NULL;
 
@@ -141,15 +140,25 @@ int snd_seq_create_port(struct snd_seq_client *client, int port,
 	port_subs_info_init(&new_port->c_dest);
 	snd_use_lock_use(&new_port->use_lock);
 
+	*port_ret = new_port;
+
+	return 0;
+}
+
+/* insert the port; return the port address or a negative error code */
+int snd_seq_insert_port(struct snd_seq_client *client, int port,
+			struct snd_seq_client_port *new_port)
+{
+	struct snd_seq_client_port *p;
+	int num;
+
 	num = max(port, 0);
 	guard(mutex)(&client->ports_mutex);
 	guard(write_lock_irq)(&client->ports_lock);
 	struct list_head *insert_before = &client->ports_list_head;
 	list_for_each_entry(p, &client->ports_list_head, list) {
-		if (p->addr.port == port) {
-			kfree(new_port);
+		if (p->addr.port == port)
 			return -EBUSY;
-		}
 		if (p->addr.port > num) {
 			insert_before = &p->list;
 			break;
@@ -162,7 +171,6 @@ int snd_seq_create_port(struct snd_seq_client *client, int port,
 	client->num_ports++;
 	new_port->addr.port = num;	/* store the port number in the port */
 	sprintf(new_port->name, "port-%d", num);
-	*port_ret = new_port;
 
 	return num;
 }
diff --git a/sound/core/seq/seq_ports.h b/sound/core/seq/seq_ports.h
index 40ed6cf7cb90..b689c0f4867c 100644
--- a/sound/core/seq/seq_ports.h
+++ b/sound/core/seq/seq_ports.h
@@ -98,10 +98,14 @@ struct snd_seq_client_port *snd_seq_port_query_nearest(struct snd_seq_client *cl
 
 DEFINE_FREE(snd_seq_port, struct snd_seq_client_port *, if (!IS_ERR_OR_NULL(_T)) snd_seq_port_unlock(_T))
 
-/* create a port, port number or a negative error code is returned */
-int snd_seq_create_port(struct snd_seq_client *client, int port_index,
+/* create a port, 0 on success or a negative error code is returned */
+int snd_seq_create_port(struct snd_seq_client *client,
 			struct snd_seq_client_port **port_ret);
 
+/* insert the port; return the port address or a negative error code */
+int snd_seq_insert_port(struct snd_seq_client *client, int port,
+			struct snd_seq_client_port *new_port);
+
 /* delete a port */
 int snd_seq_delete_port(struct snd_seq_client *client, int port);
 
-- 
2.54.0