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;
Subject: Re: [PATCH 1/1] block: Use bits.h macros to improve readability
To:     Joe Perches <joe@perches.com>,
        Leonardo Bras <leonardo@linux.ibm.com>,
        linux-kernel@vger.kernel.org
Cc:     Dennis Zhou <dennis@kernel.org>, Hannes Reinecke <hare@suse.com>,
        Damien Le Moal <damien.lemoal@wdc.com>,
        Tejun Heo <tj@kernel.org>,
        "Dennis Zhou (Facebook)" <dennisszhou@gmail.com>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        Sagi Grimberg <sagi@grimberg.me>
References: <20190802000041.24513-1-leonardo@linux.ibm.com>
 <a41b5530-f2e1-0932-1f39-0ce66ce902ae@kernel.dk>
 <15450f6ba169de8862e11bc2d20b3645958f4efd.camel@perches.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <a0ca29ac-ce51-16e7-d0b8-c90cbb4835e6@kernel.dk>
Date:   Sun, 4 Aug 2019 14:10:05 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <15450f6ba169de8862e11bc2d20b3645958f4efd.camel@perches.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 8/4/19 1:17 PM, Joe Perches wrote:
> On Fri, 2019-08-02 at 21:18 -0700, Jens Axboe wrote:
>> On 8/1/19 6:00 PM, Leonardo Bras wrote:
>>> Applies some bits.h macros in order to improve readability of
>>> linux/blk_types.h.
> []
>> I know precisely what that does, whereas I have to think about the other
>> one, maybe even look it up to be sure. For instance, without looking
>> now, I have no idea what the second argument is. Looking at the git log,
>> I see numerous instances of:
> 
> While I'm not at all a proponent of GENMASK/GENMASK_ULL,
> and so not a proponent of this patch, latent defects are
> possible in both cases.
> 
> You'd likely have to look at SOME_SHIFT to see if it's 0
> to verify the actual mask is what's really desired.
> 
> $ git grep -P '_SHIFT\s+\(?\s*0\s*\)?\b' | wc -l
> 11907

Usually SOME_SHIFT is either a numeric value, and you already know,
or it's part of a series of enums/defines (like in the case that's
being done here) where you already have prior knowledge about the
values. For those cases, GENMASK/GENMASK_ULL adds nothing imho, it
only makes it less readable and more error prone.

-- 
Jens Axboe