Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <b2087cac13c3a1d01ebe1a17e66351f3777bc397.camel@perches.com>
Subject: Re: [PATCH] checkpatch: Add a --strict test for structs with bool
 member definitions
From:   Joe Perches <joe@perches.com>
To:     Julia Lawall <julia.lawall@lip6.fr>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Andy Whitcroft <apw@canonical.com>, yuankuiz@codeaurora.org,
        Linux PM <linux-pm@vger.kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        paulmck@linux.vnet.ibm.com, Ingo Molnar <mingo@kernel.org>,
        Len Brown <len.brown@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Date:   Wed, 11 Apr 2018 23:42:20 -0700
In-Reply-To: <alpine.DEB.2.20.1804120816130.3559@hadrien>
References: <891d4f632fbff5052e11f2d0b6fac35d@codeaurora.org>
          <CAJZ5v0h=Jeb5JjjE9vNQM29xYAy-Ogmx1mycRv-hPJ1+m=edzw@mail.gmail.com>
          <20180410123305.GF4082@hirez.programming.kicks-ass.net>
          <e22fb871b1b7f2fda4b22f3a24e0d7f092eb612c.camel@perches.com>
          <95477c93db187bab6da8a8ba7c57836868446179.camel@perches.com>
          <20180410143950.4b8526073b4e3e34689f68cb@linux-foundation.org>
          <b3d75281c3a7b4b217b612913894b346eaa3288b.camel@perches.com>
          <20180410150011.df9e036f57b5bcac7ac19686@linux-foundation.org>
          <20180411081502.GJ4082@hirez.programming.kicks-ass.net>
          <20180411092959.e666ec443e4d3bb6f43901d7@linux-foundation.org>
         <1c9f185f6086e9d89659f93720a27b660ee17c13.camel@perches.com>
         <alpine.DEB.2.20.1804120816130.3559@hadrien>
Content-Type: text/plain; charset="ISO-8859-1"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, 2018-04-12 at 08:22 +0200, Julia Lawall wrote:
> On Wed, 11 Apr 2018, Joe Perches wrote:
> > On Wed, 2018-04-11 at 09:29 -0700, Andrew Morton wrote:
> > > We already have some 500 bools-in-structs
> > 
> > I got at least triple that only in include/
> > so I expect there are at probably an order
> > of magnitude more than 500 in the kernel.
> > 
> > I suppose some cocci script could count the
> > actual number of instances.  A regex can not.
> 
> I got 12667.

Could you please post the cocci script?

> I'm not sure to understand the issue.  Will using a bitfield help if there
> are no other bitfields in the structure?

IMO, not really.

The primary issue is described by Linus here:
https://lkml.org/lkml/2017/11/21/384

I personally do not find a significant issue with
uncontrolled sizes of bool in kernel structs as
all of the kernel structs are transitory and not
written out to storage.

I suppose bool bitfields are also OK, but for the
RMW required.

Using unsigned int :1 bitfield instead of bool :1
has the negative of truncation so that the uint
has to be set with !! instead of a simple assign.