From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f52.google.com (mail-wg0-f52.google.com [74.125.82.52]) by dpdk.org (Postfix) with ESMTP id AFBD5683D for ; Tue, 14 Apr 2015 17:17:48 +0200 (CEST) Received: by wgyo15 with SMTP id o15so15849535wgy.2 for ; Tue, 14 Apr 2015 08:17:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=eO/JJ4kHEO6rgwvPpJYRqJpmo5kjlvHdz82w0fztM6E=; b=fdC+BLVdxF4HfF19A82Sh3Br8/7aHOS535frH4vnToDE+l7cafi/HMSIIQ0iJVXVKY JW/qFknZXVTdjt/NB/E4D4g4GJHPdYE+6v7iM16sDGXipIn3pHjq56c1dJmQoGxk8Xw9 IET4qiqPnjR+z9qsXd1VXhpLzeRMasrzKKIXZe1RepqRATQfvzPfVtRscZQMkzhag78O YcKo9IuxOIf6J3jk02WH9K/tZZFW7gwj1R1R6dggHmnFfbiPdUVW+rr0uV3D+LtsWh/g uifvAFHAoCkM8iKE8p4VIaD5QOW/FWdC2bGWFsScVAkzIVGujMMeU+ZgXr+j3wGWe0z5 Ag8g== X-Gm-Message-State: ALoCoQlFcIi7i4b022n5+sBbAef/dTUoSYleeDMFfc5iNXtgovc5LpMeMnZS3CJwhQiMKBYbDbLW X-Received: by 10.180.218.201 with SMTP id pi9mr17092463wic.53.1429024668575; Tue, 14 Apr 2015 08:17:48 -0700 (PDT) Received: from [10.0.0.166] ([212.143.139.214]) by mx.google.com with ESMTPSA id e2sm1963212wjy.46.2015.04.14.08.17.47 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Apr 2015 08:17:48 -0700 (PDT) Message-ID: <552D2F9A.3060001@cloudius-systems.com> Date: Tue, 14 Apr 2015 18:17:46 +0300 From: Vlad Zolotarov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Thomas Monjalon References: <1429003900-20074-1-git-send-email-thomas.monjalon@6wind.com> <54963304.brPH8sEe9A@xps13> <552D247D.9040204@cloudius-systems.com> <1672329.GelmR7Xu11@xps13> In-Reply-To: <1672329.GelmR7Xu11@xps13> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix build with gcc 4.4 X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 14 Apr 2015 15:17:48 -0000 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@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? >