linux-kernel - [PATCH 06/13] Handle a non blocking read without blocking

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Message-Id: <1339057243-10029-7-git-send-email-stefani@seibold.net>
Date:	Thu,  7 Jun 2012 10:20:36 +0200
From:	stefani@...bold.net
To:	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	oneukum@...e.de
Cc:	linux-usb@...r.kernel.org, Stefani Seibold <stefani@...bold.net>
Subject: [PATCH 06/13] Handle a non blocking read without blocking

From: Stefani Seibold <stefani@...bold.net>

Signed-off-by: Stefani Seibold <stefani@...bold.net>
---
 drivers/usb/usb-skeleton.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 2ca2530..e4cb88a 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -225,9 +225,14 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count,
 		return 0;
 
 	/* no concurrent readers */
-	retval = mutex_lock_interruptible(&dev->io_mutex);
-	if (retval < 0)
-		return retval;
+	if (file->f_flags & O_NONBLOCK) {
+		if (!mutex_trylock(&dev->io_mutex))
+			return -EAGAIN;
+	} else {
+		retval = mutex_lock_interruptible(&dev->io_mutex);
+		if (retval < 0)
+			return retval;
+	}
 
 	if (!dev->interface) {		/* disconnect() was called */
 		retval = -ENODEV;
-- 
1.7.8.6

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