Re: [dpdk-dev] [PATCH v5 1/5] ethdev: add VXLAN-GPE macro

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 4/5/2019 11:37 AM, Thomas Monjalon wrote:
> Hi,
> 
> Sorry for not catching it before, but I was not Cc.
> Please use git send-email --to-cmd devtools/get-maintainer.sh
> 
> 05/04/2019 11:42, Ferruh Yigit:
>> On 4/5/2019 10:36 AM, Ananyev, Konstantin wrote:
>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Qi Zhang
>>>> From: Qiming Yang <qiming.yang@intel.com>
>>>>
>>>> This patch added VXLAN-GPE macro in rte_eth_tunnel_type.
>>>> This patch will break the ABI, RTE_TUNNEL_TYPE_MAX will have
>>>> problem when running with new version of the ethdev shared
>>>> library.
>>>>
>>>> Signed-off-by: Qiming Yang <qiming.yang@intel.com>
>>>> ---
> [...]
>>>> --- a/lib/librte_ethdev/rte_eth_ctrl.h
>>>> +++ b/lib/librte_ethdev/rte_eth_ctrl.h
>>>> @@ -229,6 +229,7 @@ enum rte_eth_tunnel_type {
>>>>  	RTE_TUNNEL_TYPE_NVGRE,
>>>>  	RTE_TUNNEL_TYPE_IP_IN_GRE,
>>>>  	RTE_L2_TUNNEL_TYPE_E_TAG,
>>>> +	RTE_TUNNEL_TYPE_VXLAN_GPE,
>>>
>>> Not sure, why do you consider it as an ABI breakage?
>>
>> I think it is API breakage instead of ABI.
>>
>> This changes the value of the 'RTE_TUNNEL_TYPE_MAX'
>> If the application is using the MAX enum item, with the new version of the
>> ethdev the MAX value will be different and this can break the app.
>>
>> Like:
>>
>> app_function(..) {
>>   ret = lib_foo()
>>   if (ret == RTE_TUNNEL_TYPE_MAX)
>>     ret -1;
>> }
>>
>> lib_foo(..) {
>>   return RTE_TUNNEL_TYPE_MAX;
>> }
>>
>>
>> When app compiled, MAX was '7' and app is comparing ret value against '7', but
>> with new version of DPDK, 'lib_foo()' will return '8' instead.
> 
> I would vote for ABI because it is a value change.
> 
> Anyway, it must be noticed in the release notes.
> 
> As we are already breaking ethdev ABI in this release,
> and it is a very basic change, I agree to accept it in 19.05.

+1

> 
> In future, we should make sure that such addition is possible
> without any breakage.

+1. Otherwise there is no escape from it and adding a new tunnel type shouldn't
cause and ABI/API breakage.