Re: [PATCH] staging:iio: Add wrapper functions around buffer access ops

[Greg KH <gregkh@suse.de>]

On Wed, Dec 14, 2011 at 11:15:49AM +0100, Lars-Peter Clausen wrote:
> On 12/14/2011 12:59 AM, Greg KH wrote:
> > 
> >>>> +static inline int buffer_get_length(struct iio_buffer *buffer)
> >>>> +{
> >>>> +	if (buffer->access->get_length)
> >>>> +		return buffer->access->get_length(buffer);
> >>>> +
> >>>> +	return -ENOSYS;
> >>>
> >>> Here you return an error, but why ENOSYS?
> >>>
> >>> Consistancy is key, and you don't have it here at all.  Or if you do, I
> >>> sure don't understand it...
> >>
> >> Well, different types of functions require different semantics. While the
> >> previous ones did either return 0 in case of success or a error value in case
> >> of an error, buffer_get_length returns an integer value where 0 is a valid
> >> value. Since we can't make any meaningful assumptions about the buffer size if
> >> the callback is not implemented we return an error value. Why ENOSYS? Because
> >> it is the code for 'function not implemented' and is used throughout the kernel
> >> in similar situations.
> > 
> > Is the caller always supposed to check this?  If so, please mark the
> > function as such so the compiler will complain if it isn't.
> 
> Marking the function as __must_check doesn't make much sense here. Since it
> will either return an error or the buffer length. So you'll always use the
> returned result one way or the other.

That's exactly the point, you must use it, so mark it as such.

greg k-h