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[109.190.92.136]) by mx.google.com with ESMTPSA id hu1sm3214525wib.6.2015.04.14.08.14.06 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Apr 2015 08:14:07 -0700 (PDT) From: Thomas Monjalon To: Vlad Zolotarov Date: Tue, 14 Apr 2015 17:13:25 +0200 Message-ID: <1704204.vBeNmeNBCG@xps13> Organization: 6WIND User-Agent: KMail/4.14.4 (Linux/3.18.4-1-ARCH; KDE/4.14.4; x86_64; ; ) In-Reply-To: <552D2B59.9000907@cloudius-systems.com> References: <1429003900-20074-1-git-send-email-thomas.monjalon@6wind.com> <54963304.brPH8sEe9A@xps13> <552D2B59.9000907@cloudius-systems.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" 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 15:14:08 -0000 2015-04-14 17:59, 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. > > > >> 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'm sorry but it's not clear to me at all since the common C practice > for zeroing the struct would be > > struct st a = {0}; > > Like in the lines u are changing. The lines as above are clearly should > not be commented and are absolutely clear. > The lines u are adding on the other hand are absolutely unclear and > confusing outside the gcc bug context. Therefore it should be clearly > stated so in a form of comment. Otherwise somebody (like myself) may see > this and immediately fix it back (as it should be). > > > I thought it is a basic C practice. > > I doubt that. ;) Explained above. > > > 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? > > OMG! This is awful! I think everybody agrees that this is a workaround > and has nothing to do with a codding style (it's an opposite to a style > actually). I don't know where this should be explained, frankly. Once we assert we want to support this buggy compiler, the workarounds are automatically parts of the coding style. I don't know how to deal differently with this constraint. > Getting back to the issue - I'm a bit surprised since I use this kind of > initializer ({0}) in a C code for quite a long time - long before 2012. > I'd like to understand what is a problem with this specific gcc version. > This seems to trivial. I'm surprised CentOS has a gcc version with this > kind of bugs. Each day brings its surprise :)