From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965306AbdEVWWd (ORCPT ); Mon, 22 May 2017 18:22:33 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:46980 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752426AbdEVWW3 (ORCPT ); Mon, 22 May 2017 18:22:29 -0400 Date: Mon, 22 May 2017 15:22:27 -0700 From: Andrew Morton To: Joe Perches Cc: Alexey Dobriyan , linux-kernel@vger.kernel.org Subject: Re: [PATCH] CodingStyle: delete "kmalloc(sizeof(*var))" as preferred allocation form Message-Id: <20170522152227.52a9a7c48e8141056fc612c4@linux-foundation.org> In-Reply-To: <1495489398.2093.48.camel@perches.com> References: <20170522213837.GA13861@avx2> <1495489398.2093.48.camel@perches.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 May 2017 14:43:18 -0700 Joe Perches wrote: > On Tue, 2017-05-23 at 00:38 +0300, Alexey Dobriyan wrote: > > There are valid reasons for > > > > malloc(sizeof(struct S)) > > > > form: > > > > * struct S acts as an anchor for ctags quickly reminding which type is > > in focus > > > > * argument re changing name prevents bugs is semi bogus: > > such changes are rare, > > "void *" cast gives both forms equal opportunity to be screwed up > > > > * proper way to fix those rare misallocation bugs (which indeed happened) > > is type safe allocation macros (see tmalloc from Samba). > > > > However amount of disruption will be so high so it may never be done. > > > > * ratio of allocation styles is ~6400:12000 which is about 1:2 > > so the amount of churn to maintain this rule is pretty high in theory. > > > > The winning move is to not play and not encourage people send trivial stuff. > > > > Signed-off-by: Alexey Dobriyan > > --- > > > > Documentation/process/coding-style.rst | 10 ---------- > > 1 file changed, 10 deletions(-) > > > > --- a/Documentation/process/coding-style.rst > > +++ b/Documentation/process/coding-style.rst > > @@ -808,16 +808,6 @@ kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and > > vzalloc(). Please refer to the API documentation for further information > > about them. > > > > -The preferred form for passing a size of a struct is the following: > > - > > -.. code-block:: c > > - > > - p = kmalloc(sizeof(*p), ...); > > - > > -The alternative form where struct name is spelled out hurts readability and > > -introduces an opportunity for a bug when the pointer variable type is changed > > -but the corresponding sizeof that is passed to a memory allocator is not. > > - > > Casting the return value which is a void pointer is redundant. The conversion > > from void pointer to any other pointer type is guaranteed by the C programming > > language. > > Thanks. I agree with this deletion. I don't. Every damn time I see a p = kmalloc(sizeof struct foo) I have to hunt around to check the type of p. And I review a lot of code!