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

From: Hannes Reinecke <hare@suse.de>
To: Nitesh Shetty <nj.shetty@samsung.com>,
	Jens Axboe <axboe@kernel.dk>, Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@kernel.org>,
	dm-devel@redhat.com, Keith Busch <kbusch@kernel.org>,
	Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	James Smart <james.smart@broadcom.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>
Cc: anuj20.g@samsung.com, joshi.k@samsung.com, p.raghav@samsung.com,
	nitheshshetty@gmail.com, gost.dev@samsung.com,
	Vincent Fu <vincent.fu@samsung.com>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 3/9] block: add emulation for copy
Date: Thu, 12 Jan 2023 15:46:16 +0100	[thread overview]
Message-ID: <bfec42d1-a1bf-3b3a-10dd-8d3db0a6e6a0@suse.de> (raw)
In-Reply-To: <20230112115908.23662-4-nj.shetty@samsung.com>

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@samsung.com>
> Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.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?

Cheers,

Hannes