staging:iio: Prevent reading from buffer chrdev when device has no buffer.

Silly bug introduced during the chrdev merge series.
Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/iio_core.h

@@ -33,7 +33,7 @@ int __iio_add_chan_devattr(const char *postfix,
 #ifdef CONFIG_IIO_BUFFER
 struct poll_table_struct;
 
-void iio_chrdev_buffer_open(struct iio_dev *indio_dev);
+int iio_chrdev_buffer_open(struct iio_dev *indio_dev);
 void iio_chrdev_buffer_release(struct iio_dev *indio_dev);
 
 unsigned int iio_buffer_poll(struct file *filp,
@@ -47,8 +47,11 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
 
 #else
 
-static inline void iio_chrdev_buffer_open(struct iio_dev *indio_dev)
-{}
+static inline int iio_chrdev_buffer_open(struct iio_dev *indio_dev)
+{
+	return -EINVAL;
+}
+
 static inline void iio_chrdev_buffer_release(struct iio_dev *indio_dev)
 {}
 

drivers/staging/iio/industrialio-buffer.c

@@ -63,11 +63,14 @@ unsigned int iio_buffer_poll(struct file *filp,
 	return 0;
 }
 
-void iio_chrdev_buffer_open(struct iio_dev *indio_dev)
+int iio_chrdev_buffer_open(struct iio_dev *indio_dev)
 {
 	struct iio_buffer *rb = indio_dev->buffer;
-	if (rb && rb->access->mark_in_use)
+	if (!rb)
+		return -EINVAL;
+	if (rb->access->mark_in_use)
 		rb->access->mark_in_use(rb);
+	return 0;
 }
 
 void iio_chrdev_buffer_release(struct iio_dev *indio_dev)
@@ -77,7 +80,6 @@ void iio_chrdev_buffer_release(struct iio_dev *indio_dev)
 	clear_bit(IIO_BUSY_BIT_POS, &rb->flags);
 	if (rb->access->unmark_in_use)
 		rb->access->unmark_in_use(rb);
-
 }
 
 void iio_buffer_init(struct iio_buffer *buffer, struct iio_dev *dev_info)

drivers/staging/iio/industrialio-core.c

@@ -1065,8 +1065,8 @@ static int iio_chrdev_open(struct inode *inode, struct file *filp)
 	struct iio_dev *dev_info = container_of(inode->i_cdev,
 						struct iio_dev, chrdev);
 	filp->private_data = dev_info;
-	iio_chrdev_buffer_open(dev_info);
-	return 0;
+
+	return iio_chrdev_buffer_open(dev_info);
 }
 
 /**