iio: core: centralize ioctl() calls to the main chardev

The aim of this is to improve a bit the organization of ioctl() calls in
IIO core. Currently the chardev is split across IIO core sub-modules/files.
The main chardev has to be able to handle ioctl() calls, and if we need to
add buffer ioctl() calls, this would complicate things.

The 'industrialio-core.c' file will provide a 'iio_device_ioctl()' which
will iterate over a list of ioctls registered with the IIO device. These
can be event ioctl() or buffer ioctl() calls, or something else.

Each ioctl() handler will have to return a IIO_IOCTL_UNHANDLED code (which
is positive 1), if the ioctl() did not handle the call in any. This
eliminates any potential ambiguities about negative error codes, which
should fail the call altogether.

If any ioctl() returns 0, it was considered that it was serviced
successfully and the loop will exit.

This change also moves the handling of the IIO_GET_EVENT_FD_IOCTL command
inside 'industrialio-event.c', where this is better suited.

This patch is a combination of 2 other patches from an older series:
Patch 1: iio: core: add simple centralized mechanism for ioctl() handlers
  Link: https://lore.kernel.org/linux-iio/20200427131100.50845-6-alexandru.ardelean@analog.com/
Patch 2: iio: core: use new common ioctl() mechanism
  Link: https://lore.kernel.org/linux-iio/20200427131100.50845-7-alexandru.ardelean@analog.com/

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20200924084155.99406-1-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 42 insertions, 14 deletions

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 0402be441ffb..e53c771d66eb 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1612,6 +1612,7 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 	}
 	dev_set_name(&dev->dev, "iio:device%d", dev->id);
 	INIT_LIST_HEAD(&iio_dev_opaque->buffer_list);
+	INIT_LIST_HEAD(&iio_dev_opaque->ioctl_handlers);
 
 	return dev;
 }
@@ -1705,26 +1706,47 @@ static int iio_chrdev_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-/* Somewhat of a cross file organization violation - ioctls here are actually
- * event related */
+void iio_device_ioctl_handler_register(struct iio_dev *indio_dev,
+				       struct iio_ioctl_handler *h)
+{
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+
+	list_add_tail(&h->entry, &iio_dev_opaque->ioctl_handlers);
+}
+
+void iio_device_ioctl_handler_unregister(struct iio_ioctl_handler *h)
+{
+	list_del(&h->entry);
+}
+
 static long iio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct iio_dev *indio_dev = filp->private_data;
-	int __user *ip = (int __user *)arg;
-	int fd;
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	struct iio_ioctl_handler *h;
+	int ret = -ENODEV;
+
+	mutex_lock(&indio_dev->info_exist_lock);
 
+	/**
+	 * The NULL check here is required to prevent crashing when a device
+	 * is being removed while userspace would still have open file handles
+	 * to try to access this device.
+	 */
 	if (!indio_dev->info)
-		return -ENODEV;
-
-	if (cmd == IIO_GET_EVENT_FD_IOCTL) {
-		fd = iio_event_getfd(indio_dev);
-		if (fd < 0)
-			return fd;
-		if (copy_to_user(ip, &fd, sizeof(fd)))
-			return -EFAULT;
-		return 0;
+		goto out_unlock;
+
+	ret = -EINVAL;
+	list_for_each_entry(h, &iio_dev_opaque->ioctl_handlers, entry) {
+		ret = h->ioctl(indio_dev, filp, cmd, arg);
+		if (ret != IIO_IOCTL_UNHANDLED)
+			break;
 	}
-	return -EINVAL;
+
+out_unlock:
+	mutex_unlock(&indio_dev->info_exist_lock);
+
+	return ret;
 }
 
 static const struct file_operations iio_buffer_fileops = {
@@ -1841,6 +1863,9 @@ EXPORT_SYMBOL(__iio_device_register);
  **/
 void iio_device_unregister(struct iio_dev *indio_dev)
 {
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	struct iio_ioctl_handler *h, *t;
+
 	cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
 
 	mutex_lock(&indio_dev->info_exist_lock);
@@ -1851,6 +1876,9 @@ void iio_device_unregister(struct iio_dev *indio_dev)
 
 	indio_dev->info = NULL;
 
+	list_for_each_entry_safe(h, t, &iio_dev_opaque->ioctl_handlers, entry)
+		list_del(&h->entry);
+
 	iio_device_wakeup_eventset(indio_dev);
 	iio_buffer_wakeup_poll(indio_dev);