From: Damien Le Moal <Damien.LeMoal@wdc.com>
To: Bart Van Assche <bvanassche@acm.org>, Jens Axboe <axboe@kernel.dk>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>, Ming Lei <ming.lei@redhat.com>,
Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
Alexander Potapenko <glider@google.com>
Subject: Re: [PATCH 5/5] null_blk: Zero-initialize read buffers in non-memory-backed mode
Date: Tue, 19 May 2020 03:03:06 +0000 [thread overview]
Message-ID: <BY5PR04MB69000C77620D48609E90D411E7B90@BY5PR04MB6900.namprd04.prod.outlook.com> (raw)
In-Reply-To: be635a33-c07c-c961-3033-cc1a9bc82e8b@acm.org
On 2020/05/18 23:31, Bart Van Assche wrote:
> On 2020-05-17 20:12, Damien Le Moal wrote:
>> On 2020/05/18 11:56, Bart Van Assche wrote:
>>> On 2020-05-17 19:10, Damien Le Moal wrote:
>>>> On 2020/05/18 10:32, Bart Van Assche wrote:
>>>>> On 2020-05-17 18:12, Damien Le Moal wrote:
>>>>>> On 2020/05/16 9:19, Bart Van Assche wrote:
>>>>>>> +static void nullb_zero_rq_data_buffer(const struct request *rq)
>>>>>>> +{
>>>>>>> + struct req_iterator iter;
>>>>>>> + struct bio_vec bvec;
>>>>>>> +
>>>>>>> + rq_for_each_bvec(bvec, rq, iter)
>>>>>>> + zero_fill_bvec(&bvec);
>>>>>>> +}
>>>>>>> +
>>>>>>> +static void nullb_zero_read_cmd_buffer(struct nullb_cmd *cmd)
>>>>>>> +{
>>>>>>> + struct nullb_device *dev = cmd->nq->dev;
>>>>>>> +
>>>>>>> + if (dev->queue_mode == NULL_Q_BIO && bio_op(cmd->bio) == REQ_OP_READ)
>>>>>>> + zero_fill_bio(cmd->bio);
>>>>>>> + else if (req_op(cmd->rq) == REQ_OP_READ)
>>>>>>> + nullb_zero_rq_data_buffer(cmd->rq);
>>>>>>> +}
>>>>>>
>>>>>> Shouldn't the definition of these two functions be under a "#ifdef CONFIG_KMSAN" ?
>>>>>
>>>>> It is on purpose that I used IS_ENABLED(CONFIG_KMSAN) below instead of
>>>>> #ifdef CONFIG_KMSAN. CONFIG_KMSAN is not yet upstream and I want to
>>>>> expose the above code to the build robot.
>>>>
>>>> But then you will get a "defined but unused" build warning, no ?
>>>
>>> Not when using IS_ENABLED(...).
>>
>> I do not understand: the "if (IS_ENABLED(CONFIG_KMSAN))" will be compiled out if
>> CONFIG_KMSAN is not enabled/defined, but the function definitions will still
>> remain, won't they ? That will lead to "defined but unused" warning, no ? What
>> am I missing here ?
>
> "if (IS_ENABLED(CONFIG_KMSAN))" won't be removed by the preprocessor.
> The preprocessor will convert it into if (0).
>
> This is what I found in the gcc documentation about -Wunused-function:
> "-Wunused-function
> Warn whenever a static function is declared but not defined or a
> non-inline static function is unused. This warning is enabled by -Wall."
> I think that "if (0) func(...)" counts as using func().
Makes sense. Thanks for the explanation.
But from code-size perspective, I think it would still make sense to add the
#ifdef CONFIG_KMSAN around the zeroing functions.
>
> Bart.
>
--
Damien Le Moal
Western Digital Research
next prev parent reply other threads:[~2020-05-19 3:03 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-16 0:19 [PATCH 0/5] Block layer patches for kernel v5.8 Bart Van Assche
2020-05-16 0:19 ` [PATCH 1/5] block: Fix type of first compat_put_{,u}long() argument Bart Van Assche
2020-05-16 7:40 ` Arnd Bergmann
2020-05-16 12:41 ` Christoph Hellwig
2020-05-16 0:19 ` [PATCH 2/5] bio.h: Declare the arguments of bio iteration functions const Bart Van Assche
2020-05-16 8:55 ` Alexander Potapenko
2020-05-16 17:10 ` Bart Van Assche
2020-05-16 12:42 ` Christoph Hellwig
2020-05-17 22:46 ` Chaitanya Kulkarni
2020-05-16 0:19 ` [PATCH 3/5] block: Document the bio_vec properties Bart Van Assche
2020-05-16 12:43 ` Christoph Hellwig
2020-05-16 0:19 ` [PATCH 4/5] block: Fix zero_fill_bio() Bart Van Assche
2020-05-16 5:50 ` Ming Lei
2020-05-16 0:19 ` [PATCH 5/5] null_blk: Zero-initialize read buffers in non-memory-backed mode Bart Van Assche
2020-05-16 9:40 ` Alexander Potapenko
2020-05-18 1:12 ` Damien Le Moal
2020-05-18 1:32 ` Bart Van Assche
2020-05-18 2:10 ` Damien Le Moal
2020-05-18 2:56 ` Bart Van Assche
2020-05-18 3:12 ` Damien Le Moal
2020-05-18 14:31 ` Bart Van Assche
2020-05-19 3:03 ` Damien Le Moal [this message]
2020-05-19 4:10 ` Bart Van Assche
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