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Subject: Re: [PATCH V3] brd: check and limit max_part par
To:     Ming Lei <ming.lei@redhat.com>
CC:     Jens Axboe <axboe@kernel.dk>, <linux-block@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Mingfangsen <mingfangsen@huawei.com>, Guiyao <guiyao@huawei.com>,
        zhangsaisai <zhangsaisai@huawei.com>,
        "wubo (T)" <wubo40@huawei.com>
References: <c8236e55-f64f-ef40-b394-8b7e86ce50df@huawei.com>
 <20200115022725.GA14585@ming.t460p>
 <ce5823ea-2183-90df-05b0-c02d1f654be3@huawei.com>
 <20200120225858.GB19571@ming.t460p>
From:   Zhiqiang Liu <liuzhiqiang26@huawei.com>
Message-ID: <1378f7d0-7166-a860-03cd-523cef8ea14b@huawei.com>
Date:   Tue, 21 Jan 2020 09:44:46 +0800
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On 2020/1/21 6:58, Ming Lei wrote:
> On Mon, Jan 20, 2020 at 09:14:50PM +0800, Zhiqiang Liu wrote:
>>>> +static inline void brd_check_and_reset_par(void)
>>>> +{
>>>> +       if (unlikely(!rd_nr))
>>>> +               rd_nr = 1;
>>>> +
>>>> +       if (unlikely(!max_part))
>>>> +               max_part = 1;
>>>
>>> Another limit is that 'max_part' needs to be divided exactly by (1U <<
>>> MINORBITS), something like:
>>>
>>> 	max_part = 1UL << fls(max_part)
>>
>> Do we have to limit that 'max_part' needs to be divided exactly by (1U <<
>>> MINORBITS)? As your suggestion, the i * max_part is larger than MINORMASK,
>> we can allocate from extended devt.
> 
> Exact dividing is for reserving same minors for all disks with
> RAMDISK_MAJOR, otherwise there is still chance to get same dev_t when
> adding partitions.
> 
> Extended devt is for covering more disks, not related with 'max_part'.
> 

Thank you very much.
I will change that as you said.