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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2015-04-14 16:38, Vlad Zolotarov:
> On 04/14/15 16:06, Ananyev, Konstantin wrote:
> > From: Vlad Zolotarov [mailto:vladz@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.

> 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?