media: Wrap file->private_data access with a helper function

Accessing file->private_data manually to retrieve the v4l2_fh pointer is
error-prone, as the field is a void * and will happily convert
implicitly to any pointer type. To avoid direct access to
file->private_data, introduce a new inline function that retrieves the
v4l2_fh pointer, and use it to replace common access patterns through
the kernel.

Changes to drivers have been generated with the following coccinelle
semantic patch:

@@
struct file *filp;
identifier fh;
@@

-       struct v4l2_fh *fh = filp->private_data;
+       struct v4l2_fh *fh = file_to_v4l2_fh(filp);

Manual changes have been applied to Documentation/ to update the usage
patterns, and to include/media/v4l2-fh.h to add the new function.

While at it, fix a typo in the title of v4l2-fh.rst: the file describes
the "file handles" API, not "file handlers".

No functional change is intended, this only paves the way to remove
direct accesses to file->private_data and make V4L2 drivers safer.
Other accesses to the field will be addressed separately.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/media/v4l2-fh.h b/include/media/v4l2-fh.h
index b5b3e00c8e6a..823fa8ebeb8f 100644
--- a/include/media/v4l2-fh.h
+++ b/include/media/v4l2-fh.h
@@ -57,6 +57,20 @@ struct v4l2_fh {
 };
 
 /**
+ * file_to_v4l2_fh - Return the v4l2_fh associated with a struct file
+ *
+ * @filp: pointer to &struct file
+ *
+ * This function should be used by drivers to retrieve the &struct v4l2_fh
+ * instance pointer stored in the file private_data instead of accessing the
+ * private_data field directly.
+ */
+static inline struct v4l2_fh *file_to_v4l2_fh(struct file *filp)
+{
+	return filp->private_data;
+}
+
+/**
  * v4l2_fh_init - Initialise the file handle.
  *
  * @fh: pointer to &struct v4l2_fh