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

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

[Takashi Sakamoto]

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
71c3797779d3 ("ALSA: firewire-motu: add hwdep interface"), and persisted
when POLLOUT was updated to EPOLLOUT by a commit a9a08845e9ac ('vfs: do
bulk POLL* -> EPOLL* replacement("").').

This commit fixes the bug.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
---
 sound/firewire/motu/motu-hwdep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/firewire/motu/motu-hwdep.c b/sound/firewire/motu/motu-hwdep.c
index 1ed60618220d..fa2685665db3 100644
--- 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)
-- 
2.48.1

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

[Takashi Iwai]

On Sat, 30 Aug 2025 01:37:49 +0200,
Takashi Sakamoto wrote:
> 
> 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
> 71c3797779d3 ("ALSA: firewire-motu: add hwdep interface"), and persisted
> when POLLOUT was updated to EPOLLOUT by a commit a9a08845e9ac ('vfs: do
> bulk POLL* -> EPOLL* replacement("").').
> 
> This commit fixes the bug.
> 
> Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Thanks, applied now.


Takashi