libv4l: Document that passing in NULL as 3th arg to v4l2_ioctl is not allowed

From: Hans de Goede <hdegoede@redhat.com>

libv4l: Document that passing in NULL as 3th arg to v4l2_ioctl is not allowed

Priority: normal

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/v4l2-apps/libv4l/include/libv4l2.h b/v4l2-apps/libv4l/include/libv4l2.h
index 5488b2b10..dfae21471 100644
--- a/v4l2-apps/libv4l/include/libv4l2.h
+++ b/v4l2-apps/libv4l/include/libv4l2.h
@@ -51,6 +51,13 @@ LIBV4L_PUBLIC extern FILE *v4l2_log_file;
    Note the device name passed to v4l2_open must be of a video4linux2 device,
    if it is anything else (including a video4linux1 device), v4l2_open will
    fail.
+
+   Note that the argument to v4l2_ioctl after the request must be a valid
+   memory address of structure of the appropriate type for the request (for
+   v4l2 requests which expect a structure address). Passing in NULL or an
+   invalid memory address will not lead to failure with errno being EFAULT,
+   as it would with a real ioctl, but will cause libv4l2 to break, and you
+   get to keep both pieces.
 */
 
 LIBV4L_PUBLIC int v4l2_open (const char *file, int oflag, ...);