[dpdk-dev] [PATCH v2 4/4] add ABI checks

[Ferruh Yigit]

On 1/30/2020 3:59 PM, Thomas Monjalon wrote:
> 30/01/2020 14:06, Trahe, Fiona:
>> We were unaware the LIST_END change could constitute an ABI breakage, but can see how it affects the array size when picked up.
>> We're exploring options.
>>
>> I agree with Anoob's point that if we don't allow the LIST_END to be modified, then it means no feature can be implemented without ABI breakage.
>> Anyone  object to removing those LIST_END elements - or have a better suggestion? Would have to be in 20.11 I suppose.
> 
> Yes, having max value right after the last value is ridiculous,
> it prevents adding any value.
> In 20.11, we should remove all these *_END and *_MAX from API enums
> and replace them with a separate #define with reasonnable maximums.
> 
>

I disagree, that kind of usage is common and lets loops iterate on the valid
elements, and it is not a source of ABI break on its own.
Indeed other way around, not having MAX, is problematic, if we don't have the
MAX value to compare and decide if a provided value is valid or not, and when
new version of the library introduces the new values, how old application can
detect unsupported new values?

As far as I can see the problem occurs when that *_END and *_MAX used to define
the size of array in the public struct. This usage prevents adding new values
and I already send a deprecation notice for it:
https://patches.dpdk.org/patch/65359/