[PATCH 4/8] staging:iio: Make sure a device is only opened once at a time

[Lars-Peter Clausen <lars@metafoo.de>]

Our buffer implementation does not support multiple concurrent readers. So we
have to ensure that a device is only opened once at a time. So do the same thing
we do for the event fd and introduce a per device busy flag. The flag gets set
when opening the device and gets cleared when closing the device. If a open is
attempted while the busy flag is set we return -EBUSY.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
---
 drivers/staging/iio/iio.h               |    3 +++
 drivers/staging/iio/industrialio-core.c |   17 ++++++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/iio/iio.h b/drivers/staging/iio/iio.h
index 6b57a79..3be99fd 100644
--- a/drivers/staging/iio/iio.h
+++ b/drivers/staging/iio/iio.h
@@ -318,6 +318,7 @@ struct iio_buffer_setup_ops {
  * @chrdev:		[INTERN] associated character device
  * @groups:		[INTERN] attribute groups
  * @groupcounter:	[INTERN] index of next attribute group
+ * @flags:		[INTERN] file ops related flags including busy flag.
  **/
 struct iio_dev {
 	int				id;
@@ -349,6 +350,8 @@ struct iio_dev {
 #define IIO_MAX_GROUPS 6
 	const struct attribute_group	*groups[IIO_MAX_GROUPS + 1];
 	int				groupcounter;
+
+	unsigned long			flags;
 };
 
 /**
diff --git a/drivers/staging/iio/industrialio-core.c b/drivers/staging/iio/industrialio-core.c
index 2eef85f..12d1576 100644
--- a/drivers/staging/iio/industrialio-core.c
+++ b/drivers/staging/iio/industrialio-core.c
@@ -1083,9 +1083,18 @@ static int iio_chrdev_open(struct inode *inode, struct file *filp)
 {
 	struct iio_dev *indio_dev = container_of(inode->i_cdev,
 						struct iio_dev, chrdev);
+	unsigned int ret;
+
+	if (test_and_set_bit(IIO_BUSY_BIT_POS, &indio_dev->flags))
+		return -EBUSY;
+
 	filp->private_data = indio_dev;
 
-	return iio_chrdev_buffer_open(indio_dev);
+	ret = iio_chrdev_buffer_open(indio_dev);
+	if (ret < 0)
+		clear_bit(IIO_BUSY_BIT_POS, &indio_dev->flags);
+
+	return ret;
 }
 
 /**
@@ -1093,8 +1102,10 @@ static int iio_chrdev_open(struct inode *inode, struct file *filp)
  **/
 static int iio_chrdev_release(struct inode *inode, struct file *filp)
 {
-	iio_chrdev_buffer_release(container_of(inode->i_cdev,
-					     struct iio_dev, chrdev));
+	struct iio_dev *indio_dev = container_of(inode->i_cdev,
+						struct iio_dev, chrdev);
+	iio_chrdev_buffer_release(indio_dev);
+	clear_bit(IIO_BUSY_BIT_POS, &indio_dev->flags);
 	return 0;
 }
 
-- 
1.7.7.3