linux-kernel - [PATCH 1/2] ALSA: line6: hwdep: add support for O

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Message-Id: <20200502193120.79115-2-anarsoul@gmail.com>
Date:   Sat,  2 May 2020 12:31:19 -0700
From:   Vasily Khoruzhick <anarsoul@...il.com>
To:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Pavel Machek <pavel@...x.de>,
        Allison Randal <allison@...utok.net>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Cc:     Vasily Khoruzhick <anarsoul@...il.com>
Subject: [PATCH 1/2] ALSA: line6: hwdep: add support for O_NONBLOCK opening mode

Currently line6 hwdep interface ignores O_NONBLOCK flag when
opening device and it renders it somewhat useless when using poll.

Check for O_NONBLOCK flag when opening device and don't block read()
if it is set.

Signed-off-by: Vasily Khoruzhick <anarsoul@...il.com>
---
 sound/usb/line6/driver.c | 4 ++++
 sound/usb/line6/driver.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index 4f096685ed65..86adf87d57f0 100644
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -550,6 +550,7 @@ static int line6_hwdep_open(struct snd_hwdep *hw, struct file *file)
 	/* NOTE: hwdep layer provides atomicity here */
 
 	line6->messages.active = 1;
+	line6->messages.nonblock = file->f_flags & O_NONBLOCK ? 1 : 0;
 
 	return 0;
 }
@@ -579,6 +580,9 @@ line6_hwdep_read(struct snd_hwdep *hwdep, char __user *buf, long count,
 	while (kfifo_len(&line6->messages.fifo) == 0) {
 		mutex_unlock(&line6->messages.read_lock);
 
+		if (line6->messages.nonblock)
+			return -EAGAIN;
+
 		rv = wait_event_interruptible(
 			line6->messages.wait_queue,
 			kfifo_len(&line6->messages.fifo) != 0);
diff --git a/sound/usb/line6/driver.h b/sound/usb/line6/driver.h
index e5e572ed5f30..1a4e3700c80c 100644
--- a/sound/usb/line6/driver.h
+++ b/sound/usb/line6/driver.h
@@ -163,6 +163,7 @@ struct usb_line6 {
 		struct mutex read_lock;
 		wait_queue_head_t wait_queue;
 		unsigned int active:1;
+		unsigned int nonblock:1;
 		STRUCT_KFIFO_REC_2(LINE6_BUFSIZE_LISTEN * LINE6_RAW_MESSAGES_MAXCOUNT)
 			fifo;
 	} messages;
-- 
2.26.2