char: misc: document behaviour of open()

an open syscall now assignes file->private_data to a pointer to the
miscdevice structure. This reminds people not to duplicate code if
they want this and not to depend on it being NULL.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index ffa97d261cf3..c892c296a4de 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -169,7 +169,9 @@ static const struct file_operations misc_fops = {
  *      the minor number requested is used.
  *
  *      The structure passed is linked into the kernel and may not be
- *      destroyed until it has been unregistered.
+ *      destroyed until it has been unregistered. By default, an open()
+ *      syscall to the device sets file->private_data to point to the
+ *      structure. Drivers don't need open in fops for this.
  *
  *      A zero is returned on success and a negative errno code for
  *      failure.