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

[Lars-Peter Clausen <lars@metafoo.de>]

On 12/14/2011 04:49 PM, Greg KH wrote:
> 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.
> 
So by that logic all functions without side effects should be marked as
__must_check?

- Lars