Re: Possible bug with snd_seq_event_input_pending

[Takashi Iwai <tiwai@suse.de>]

On Sun, 02 Feb 2025 00:11:51 +0100,
Carlos wrote:
> 
> Hi, I don't know if this is a bug or not, but I'll report it in case it is.
> 
> If I configure my client as follows:
> 
> snd_seq_set_client_midi_version(seq, SND_SEQ_CLIENT_LEGACY_MIDI);
> 
> snd_seq_set_client_ump_conversion(seq, 0);//I disable ump conversion
> 
> And then I send a midi event from a MIDI 2.0 device, the
> snd_seq_event_input_pending(seq, 1) function will not respond until it
> receives any other legacy event.
> 
> Now I know that with SND_SEQ_CLIENT_LEGACY_MIDI I shouldn't disable
> ump conversion, but I expected it to return 0.

This can be indeed a problem in the kernel side.  It shouldn't deliver
the UMP events if the destination can't handle it.

Could you try the patch below?


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: seq: Drop UMP events when no UMP-conversion is set

When a destination client is a user client in the legacy MIDI mode and
it sets the no-UMP-conversion flag, currently the all UMP events are
still passed as-is.  But this may confuse the user-space, because the
event packet size is different from the legacy mode.

Since we cannot handle UMP events in user clients unless it's running
in the UMP client mode, we should filter out those events instead of
accepting blindly.  This patch addresses it by slightly adjusting the
conditions for UMP event handling at the event delivery time.

Fixes: 329ffe11a014 ("ALSA: seq: Allow suppressing UMP conversions")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/seq/seq_clientmgr.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 073b56dc2225..cb66ec42a3f8 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -678,12 +678,18 @@ static int snd_seq_deliver_single_event(struct snd_seq_client *client,
 					  dest_port->time_real);
 
 #if IS_ENABLED(CONFIG_SND_SEQ_UMP)
-	if (!(dest->filter & SNDRV_SEQ_FILTER_NO_CONVERT)) {
-		if (snd_seq_ev_is_ump(event)) {
+	if (snd_seq_ev_is_ump(event)) {
+		if (!(dest->filter & SNDRV_SEQ_FILTER_NO_CONVERT)) {
 			result = snd_seq_deliver_from_ump(client, dest, dest_port,
 							  event, atomic, hop);
 			goto __skip;
-		} else if (snd_seq_client_is_ump(dest)) {
+		} else if (dest->type == USER_CLIENT &&
+			   !snd_seq_client_is_ump(dest)) {
+			result = 0; // drop the event
+			goto __skip;
+		}
+	} else if (snd_seq_client_is_ump(dest)) {
+		if (!(dest->filter & SNDRV_SEQ_FILTER_NO_CONVERT)) {
 			result = snd_seq_deliver_to_ump(client, dest, dest_port,
 							event, atomic, hop);
 			goto __skip;
-- 
2.43.0