[dpdk-dev] [PATCH] ixgbe: fix build with gcc 4.4

Vlad Zolotarov vladz at cloudius-systems.com
Tue Apr 14 16:30:21 CEST 2015

On 04/14/15 17:17, Thomas Monjalon wrote:
> 2015-04-14 16:38, Vlad Zolotarov:
>> On 04/14/15 16:06, Ananyev, Konstantin wrote:
>>> From: Vlad Zolotarov [mailto:vladz at cloudius-systems.com]
>>>> On 04/14/15 12:31, Thomas Monjalon wrote:
>>>>> -	struct rte_eth_dev_info dev_info = { 0 };
>>>>> +	struct rte_eth_dev_info dev_info = { .max_rx_queues = 0 };
>>>> Hmmm... Unless I miss something this and one above would zero only a
>>>> single field - "max_rx_queues"; and would leave the rest uninitialized.
>>>> The original code intend to zero the whole struct. The alternative to
>>>> the original lines could be usage of memset().
>>> As I understand, in that case compiler had to set all non-explicitly initialised members to 0.
>>> So I think we are ok here.
>> Yeah, I guess it does zero-initializes the rest
>> (https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html) however I
>> don't understand how the above change fixes the error if it complains
>> about the dev_info.driver_name?
> As only 1 field is required, I chose the one which should not be removed
> from this structure in the future.

I don't follow - where/why only one field is required? The function u 
are patching uses "rx_offload_capa" field. Or u mean this gcc version 
requires only one field? If so, could u, please, provide the errata u 
are referring, since standard doesn't require any field and {0} is an 
absolutely legal (and proper) initializer in this case...

>> What I'm trying to say - the proposed fix is completely unclear and
>> confusing. Think of somebody reading this line in a month from today -
>> he wouldn't get a clue why is it there, why to explicitly set
>> max_rx_queues to zero and leave the rest be zeroed automatically... Why
>> to add such artifacts to the code instead of just zeroing the struct
>> with a memset() and putting a good clear comment above it explaining why
>> we use a memset() and not and initializer?
> We can make it longer yes.
> I think you agree we should avoid extra lines if not needed.
> In this case, when reading "= { .field = 0 }", it seems clear our goal
> is to zero the structure (it is to me).
> I thought it is a basic C practice.
> You should try "git grep '\.[^ ]\+ *= *0 *}'" to be convinced that we are
> not going to comment each occurence of this coding style.
> But it must be explained in the coding style document. Agree?

More information about the dev mailing list