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Subject: Re: [PATCH 0/4] block: Add support for REQ_OP_ASSIGN_RANGE
To:     "Martin K. Petersen" <martin.petersen@oracle.com>
Cc:     Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>, hch@lst.de,
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 <yq1v9mi4o31.fsf@oracle.com>
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
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Date:   Thu, 2 Apr 2020 12:49:15 +0300
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On 02/04/2020 05.29, Martin K. Petersen wrote:
> 
> Konstantin,
> 
>>> The corresponding exported primitive is called
>>> blkdev_issue_assign_range().
>>
>> What exact semantics of that?
> 
> REQ_OP_ALLOCATE will be used to compel a device to allocate a block
> range. What a given block contains after successful allocation is
> undefined (depends on the device implementation).

Ok. Then REQ_OP_ALLOCATE should be accounted as discard rather than write.
That's decided by helper op_is_discard() which is used only by statistics.
It seems REQ_OP_SECURE_ERASE also should be accounted in this way.

> 
> For block allocation with deterministic zeroing, one must keep using
> REQ_OP_WRITE_ZEROES with the NOUNMAP flag set.
>