linux-kernel - Re: [PATCH v6 3/9] block: add emulation for copy

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Date:   Thu, 12 Jan 2023 15:48:32 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Nitesh Shetty <nj.shetty@...sung.com>,
        Jens Axboe <axboe@...nel.dk>, Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
        Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <james.smart@...adcom.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     anuj20.g@...sung.com, joshi.k@...sung.com, p.raghav@...sung.com,
        nitheshshetty@...il.com, gost.dev@...sung.com,
        Vincent Fu <vincent.fu@...sung.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v6 3/9] block: add emulation for copy

On 1/12/23 15:46, Hannes Reinecke wrote:
> On 1/12/23 12:58, Nitesh Shetty wrote:
>> For the devices which does not support copy, copy emulation is
>> added. Copy-emulation is implemented by reading from source ranges
>> into memory and writing to the corresponding destination asynchronously.
>> For zoned device we maintain a linked list of read submission and try to
>> submit corresponding write in same order.
>> Also emulation is used, if copy offload fails or partially completes.
>>
>> Signed-off-by: Nitesh Shetty <nj.shetty@...sung.com>
>> Signed-off-by: Vincent Fu <vincent.fu@...sung.com>
>> Signed-off-by: Anuj Gupta <anuj20.g@...sung.com>
>> ---
>>   block/blk-lib.c        | 241 ++++++++++++++++++++++++++++++++++++++++-
>>   block/blk-map.c        |   4 +-
>>   include/linux/blkdev.h |   3 +
>>   3 files changed, 245 insertions(+), 3 deletions(-)
>>
> I'm not sure if I agree with this one.
> 
> You just submitted a patch for device-mapper to implement copy offload, 
> which (to all intents and purposes) _is_ an emulation.
> 
> So why do we need to implement it in the block layer as an emulation?
> Or, if we have to, why do we need the device-mapper emulation?
> This emulation will be doing the same thing, no?
> 
Sheesh. One should read the entire patchset.

Disregard the above comment.

Cheers,

Hannes