ALSA: firewire-motu: drop EPOLLOUT from poll return values as write is not supported

takaswie · tiwai · commit aea3493246c4 · 2025-08-30T09:32:45.000+02:00
The ALSA HwDep character device of the firewire-motu driver incorrectly returns EPOLLOUT in poll(2), even though the driver implements no operation for write(2). This misleads userspace applications to believe write() is allowed, potentially resulting in unnecessarily wakeups. This issue dates back to the driver's initial code added by a commit 71c3797 ("ALSA: firewire-motu: add hwdep interface"), and persisted when POLLOUT was updated to EPOLLOUT by a commit a9a0884 ('vfs: do bulk POLL* -> EPOLL* replacement("").'). This commit fixes the bug. Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Link: https://patch.msgid.link/20250829233749.366222-1-o-takashi@sakamocchi.jp Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/firewire/motu/motu-hwdep.c b/sound/firewire/motu/motu-hwdep.c
@@ -111,7 +111,7 @@ static __poll_t hwdep_poll(struct snd_hwdep *hwdep, struct file *file,
 		events = 0;
 	spin_unlock_irq(&motu->lock);
 
-	return events | EPOLLOUT;
+	return events;
 }
 
 static int hwdep_get_info(struct snd_motu *motu, void __user *arg)

Original file line number	Diff line number	Diff line change
`@@ -111,7 +111,7 @@ static __poll_t hwdep_poll(struct snd_hwdep hwdep, struct file file,`
`111`	`111`	`events = 0;`
`112`	`112`	`spin_unlock_irq(&motu->lock);`
`113`	`113`
`114`		`- return events \| EPOLLOUT;`
	`114`	`+ return events;`
`115`	`115`	`}`
`116`	`116`
`117`	`117`	`static int hwdep_get_info(struct snd_motu motu, void __user arg)`