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Subject: Re: [PATCH v2 4/5] blk-iocost: fix sleeping in atomic context
 warnning
To:     Yu Kuai <yukuai1@huaweicloud.com>, Tejun Heo <tj@kernel.org>,
        Jens Axboe <axboe@kernel.dk>
Cc:     hch@lst.de, josef@toxicpanda.com, cgroups@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
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From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <f227e4bd-c74b-a02e-2a02-11a1376ee4f9@huaweicloud.com>
Date:   Mon, 5 Dec 2022 17:39:33 +0800
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Hi, Tejun

?? 2022/11/23 18:22, Yu Kuai д??:
> Hi, Tejun
> 
> ?? 2022/11/23 8:42, Tejun Heo д??:
>> On Tue, Nov 22, 2022 at 05:14:29PM -0700, Jens Axboe wrote:
>>>>> Then match_strdup() and kfree() in match_NUMBER() can be replaced with
>>>>> get_buffer() and put_buffer().
>>>>
>>>> Sorry about the late reply. Yeah, something like this.
> 

I wonder can we just use arary directly in stack? The max size is just
24 bytes, which should be fine:

HEX: "0xFFFFFFFFFFFFFFFF" --> 18
DEC: "18446744073709551615" --> 20
OCT: "01777777777777777777777" --> 23

Something like:
#define U64_MAX_SIZE 23
static int match_strdup_local(const substring_t *s, char *buf)
{
	size_t len = s->to - s->from;

	if (len > U64_MAX_SIZE)
		return -ERANGE;

	if (!s->from)
		return -EINVAL;

	memcpy(buf, s->from, len);
	buf[len] = '\0';
	return 0;
}

  static int match_u64int(substring_t *s, u64 *result, int base)
  {
	char buf[U64_MAX_SIZE + 1];
  	int ret;
  	u64 val;

	ret = match_strdup_local(s, buf);
	if (ret)
		return ret;
  	ret = kstrtoull(buf, base, &val);
  	if (!ret)
  		*result = val;;
  	return ret;
  }