On 04/14/15 17:53, Thomas Monjalon wrote: > 2015-04-14 17:30, Vlad Zolotarov: >> 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... > Honestly I don't really care what is "legal". The most important is to make > it working with most C compilers with minimal overhead.
It's not just a "legal" - it's the most correct and robust way of initializing the struct that is promised to always work correctly. See here http://stackoverflow.com/questions/11152160/initializing-a-struct-to-0. What u hit here is (as appears) a well known Bug #53119 in gcc (see here https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53119). Have u considered adding the compilation options like -Wno-missing-braces that would silence this warning for say gcc versions below 4.7? > You're right about the variable choice: rx_offload_capa is more appropriate. > Are you OK for a v2 replacing max_rx_queues by rx_offload_capa? > >>>> 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? >
