linux-kernel - Re: [PATCH v20 02/12] Add infrastructure for copy offload in block and request layer.

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Message-ID: <b5d93f2c-29fc-4ee4-9936-0f134abc8063@acm.org>
Date: Tue, 25 Jun 2024 11:18:56 -0700
From: Bart Van Assche <bvanassche@....org>
To: Damien Le Moal <dlemoal@...nel.org>, Nitesh Shetty
 <nj.shetty@...sung.com>, Christoph Hellwig <hch@....de>
Cc: Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>,
 Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
 Mikulas Patocka <mpatocka@...hat.com>, Keith Busch <kbusch@...nel.org>,
 Sagi Grimberg <sagi@...mberg.me>, Chaitanya Kulkarni <kch@...dia.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 martin.petersen@...cle.com, david@...morbit.com, hare@...e.de,
 damien.lemoal@...nsource.wdc.com, anuj20.g@...sung.com, joshi.k@...sung.com,
 nitheshshetty@...il.com, gost.dev@...sung.com, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org,
 linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 02/12] Add infrastructure for copy offload in block
 and request layer.

On 6/24/24 2:55 PM, Damien Le Moal wrote:
> I am still a little confused as to why we need 2 BIOs, one for src and one for
> dst... Is it because of the overly complex scsi extended copy support ?
> 
> Given that the main use case is copy offload for data within the same device,
> using a single BIO which somehow can carry a list of LBA sources and a single
> destination LBA would be far simpler and perfectly matching nvme simple copy and
> ATA write gathered. And I think that this would also match the simplest case for
> scsi extended copy as well.

Hi Damien,

What are the implications for the device mapper code if the copy source
and destination LBAs are encoded in the bio payload instead of in
bio->bi_sector?

Thanks,

Bart.