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>

drivers/iio/iio_core.h

@@ -17,6 +17,20 @@ struct iio_dev;
 
 extern struct device_type iio_device_type;
 
+#define IIO_IOCTL_UNHANDLED	1
+struct iio_ioctl_handler {
+	struct list_head entry;
+	long (*ioctl)(struct iio_dev *indio_dev, struct file *filp,
+		      unsigned int cmd, unsigned long arg);
+};
+
+long iio_device_ioctl(struct iio_dev *indio_dev, struct file *filp,
+		      unsigned int cmd, unsigned long arg);
+
+void iio_device_ioctl_handler_register(struct iio_dev *indio_dev,
+				       struct iio_ioctl_handler *h);
+void iio_device_ioctl_handler_unregister(struct iio_ioctl_handler *h);
+
 int __iio_add_chan_devattr(const char *postfix,
 			   struct iio_chan_spec const *chan,
 			   ssize_t (*func)(struct device *dev,
@@ -74,7 +88,6 @@ static inline void iio_buffer_wakeup_poll(struct iio_dev *indio_dev) {}
 int iio_device_register_eventset(struct iio_dev *indio_dev);
 void iio_device_unregister_eventset(struct iio_dev *indio_dev);
 void iio_device_wakeup_eventset(struct iio_dev *indio_dev);
-int iio_event_getfd(struct iio_dev *indio_dev);
 
 struct iio_event_interface;
 bool iio_event_enabled(const struct iio_event_interface *ev_int);

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;
+		goto out_unlock;
 
-	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;
+	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);
 

drivers/iio/industrialio-event.c

@@ -31,6 +31,7 @@
  * @flags:		file operations related flags including busy flag.
  * @group:		event interface sysfs attribute group
  * @read_lock:		lock to protect kfifo read operations
+ * @ioctl_handler:	handler for event ioctl() calls
  */
 struct iio_event_interface {
 	wait_queue_head_t	wait;
@@ -40,6 +41,7 @@ struct iio_event_interface {
 	unsigned long		flags;
 	struct attribute_group	group;
 	struct mutex		read_lock;
+	struct iio_ioctl_handler	ioctl_handler;
 };
 
 bool iio_event_enabled(const struct iio_event_interface *ev_int)
@@ -187,7 +189,7 @@ static const struct file_operations iio_event_chrdev_fileops = {
 	.llseek = noop_llseek,
 };
 
-int iio_event_getfd(struct iio_dev *indio_dev)
+static int iio_event_getfd(struct iio_dev *indio_dev)
 {
 	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
 	struct iio_event_interface *ev_int = iio_dev_opaque->event_interface;
@@ -473,6 +475,24 @@ static void iio_setup_ev_int(struct iio_event_interface *ev_int)
 	mutex_init(&ev_int->read_lock);
 }
 
+static long iio_event_ioctl(struct iio_dev *indio_dev, struct file *filp,
+			    unsigned int cmd, unsigned long arg)
+{
+	int __user *ip = (int __user *)arg;
+	int fd;
+
+	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;
+	}
+
+	return IIO_IOCTL_UNHANDLED;
+}
+
 static const char *iio_event_group_name = "events";
 int iio_device_register_eventset(struct iio_dev *indio_dev)
 {
@@ -526,6 +546,10 @@ int iio_device_register_eventset(struct iio_dev *indio_dev)
 		ev_int->group.attrs[attrn++] = &p->dev_attr.attr;
 	indio_dev->groups[indio_dev->groupcounter++] = &ev_int->group;
 
+	ev_int->ioctl_handler.ioctl = iio_event_ioctl;
+	iio_device_ioctl_handler_register(&iio_dev_opaque->indio_dev,
+					  &ev_int->ioctl_handler);
+
 	return 0;
 
 error_free_setup_event_lines:
@@ -558,6 +582,8 @@ void iio_device_unregister_eventset(struct iio_dev *indio_dev)
 
 	if (ev_int == NULL)
 		return;
+
+	iio_device_ioctl_handler_unregister(&ev_int->ioctl_handler);
 	iio_free_chan_devattr_list(&ev_int->dev_attr_list);
 	kfree(ev_int->group.attrs);
 	kfree(ev_int);

include/linux/iio/iio-opaque.h

@@ -11,6 +11,7 @@
  * @channel_attr_list:		keep track of automatically created channel
  *				attributes
  * @chan_attr_group:		group for all attrs in base directory
+ * @ioctl_handlers:		ioctl handlers registered with the core handler
  * @debugfs_dentry:		device specific debugfs dentry
  * @cached_reg_addr:		cached register address for debugfs reads
  * @read_buf:			read buffer to be used for the initial reg read
@@ -22,6 +23,7 @@ struct iio_dev_opaque {
 	struct list_head		buffer_list;
 	struct list_head		channel_attr_list;
 	struct attribute_group		chan_attr_group;
+	struct list_head		ioctl_handlers;
 #if defined(CONFIG_DEBUG_FS)
 	struct dentry			*debugfs_dentry;
 	unsigned			cached_reg_addr;