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Date:   Mon, 2 Oct 2023 12:27:52 +0100
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Subject: Re: [PATCH 18/21] scsi: sd: Support reading atomic properties from
 block limits VPD
To:     Bart Van Assche <bvanassche@acm.org>, axboe@kernel.dk,
        kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
        jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org,
        viro@zeniv.linux.org.uk, brauner@kernel.org,
        chandan.babu@oracle.com, dchinner@redhat.com
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
        linux-api@vger.kernel.org
References: <20230929102726.2985188-1-john.g.garry@oracle.com>
 <20230929102726.2985188-19-john.g.garry@oracle.com>
 <2e5af8a4-f2e1-4c2e-bd0b-14cc9894b48e@acm.org>
Content-Language: en-US
From:   John Garry <john.g.garry@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <2e5af8a4-f2e1-4c2e-bd0b-14cc9894b48e@acm.org>
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On 29/09/2023 18:54, Bart Van Assche wrote:
> On 9/29/23 03:27, John Garry wrote:
>> +static void sd_config_atomic(struct scsi_disk *sdkp)
>> +{
>> +    unsigned int logical_block_size = sdkp->device->sector_size;
>> +    struct request_queue *q = sdkp->disk->queue;
>> +
>> +    if (sdkp->max_atomic) {
> 
> Please use the "return early" style here to keep the indentation
> level in this function low.

ok, fine.

> 
>> +        unsigned int max_atomic = max_t(unsigned int,
>> +            rounddown_pow_of_two(sdkp->max_atomic),
>> +            rounddown_pow_of_two(sdkp->max_atomic_with_boundary));
>> +        unsigned int unit_min = sdkp->atomic_granularity ?
>> +            rounddown_pow_of_two(sdkp->atomic_granularity) :
>> +            physical_block_size_sectors;
>> +        unsigned int unit_max = max_atomic;
>> +
>> +        if (sdkp->max_atomic_boundary)
>> +            unit_max = min_t(unsigned int, unit_max,
>> +                rounddown_pow_of_two(sdkp->max_atomic_boundary));
> 
> Why does "rounddown_pow_of_two()" occur in the above code?

I assume that you are talking about all the code above to calculate 
atomic write values for the device.

The reason is that atomic write unit min and max are always a power-of-2 
- see rules described earlier - as so that we why we rounddown to a 
power-of-2.

Thanks,
John