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Message-ID: <46e95412-9a79-51f8-3d52-caed4875d41f@opensource.wdc.com>
Date:   Mon, 2 May 2022 21:54:55 +0900
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Subject: Re: [PATCH v4 00/10] Add Copy offload support
Content-Language: en-US
To:     Dave Chinner <david@fromorbit.com>,
        Nitesh Shetty <nj.shetty@samsung.com>
Cc:     linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
        dm-devel@redhat.com, linux-nvme@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, nitheshshetty@gmail.com,
        linux-kernel@vger.kernel.org
References: <CGME20220426101804epcas5p4a0a325d3ce89e868e4924bbdeeba6d15@epcas5p4.samsung.com>
 <20220426101241.30100-1-nj.shetty@samsung.com>
 <6a85e8c8-d9d1-f192-f10d-09052703c99a@opensource.wdc.com>
 <20220427124951.GA9558@test-zns>
 <20220502040951.GC1360180@dread.disaster.area>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <20220502040951.GC1360180@dread.disaster.area>
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On 2022/05/02 13:09, Dave Chinner wrote:
> On Wed, Apr 27, 2022 at 06:19:51PM +0530, Nitesh Shetty wrote:
>> O Wed, Apr 27, 2022 at 11:19:48AM +0900, Damien Le Moal wrote:
>>> On 4/26/22 19:12, Nitesh Shetty wrote:
>>>> The patch series covers the points discussed in November 2021 virtua=
l call
>>>> [LSF/MM/BFP TOPIC] Storage: Copy Offload[0].
>>>> We have covered the Initial agreed requirements in this patchset.
>>>> Patchset borrows Mikulas's token based approach for 2 bdev
>>>> implementation.
>>>>
>>>> Overall series supports =E2=80=93
>>>>
>>>> 1. Driver
>>>> - NVMe Copy command (single NS), including support in nvme-target (f=
or
>>>>     block and file backend)
>>>
>>> It would also be nice to have copy offload emulation in null_blk for =
testing.
>>>
>>
>> We can plan this in next phase of copy support, once this series settl=
es down.
>=20
> Why not just hook the loopback driver up to copy_file_range() so
> that the backend filesystem can just reflink copy the ranges being
> passed? That would enable testing on btrfs, XFS and NFSv4.2 hosted
> image files without needing any special block device setup at all...

That is a very good idea ! But that will cover only the non-zoned case. F=
or copy
offload on zoned devices, adding support in null_blk is probably the simp=
lest
thing to do.

>=20
> i.e. I think you're doing this compeltely backwards by trying to
> target non-existent hardware first....
>=20
> Cheers,
>=20
> Dave.


--=20
Damien Le Moal
Western Digital Research