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

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Date: Fri, 31 May 2024 16:45:05 -0700
From: Bart Van Assche <bvanassche@....org>
To: Nitesh Shetty <nj.shetty@...sung.com>
Cc: Damien Le Moal <dlemoal@...nel.org>, 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>, Christoph Hellwig <hch@....de>,
 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 5/31/24 03:17, Nitesh Shetty wrote:
> I see the following challenges with bio-chained approach.
> 1. partitioned device:
>      We need to add the code which iterates over all bios and adjusts
>      the sectors offsets.
> 2. dm/stacked device:
>      We need to make major changes in dm, such as allocating cloned
>      bios, IO splits, IO offset mappings. All of which need to
>      iterate over chained BIOs.
> 
> Overall with chained BIOs we need to add a special handling only for copy
> to iterate over chained BIOs and do the same thing which is being done
> for single BIO at present.
> Or am I missing something here ?

Hmm ... aren't chained bios submitted individually? See e.g.
bio_chain_and_submit(). In other words, it shouldn't be necessary to
add any code that iterates over bio chains.

Thanks,

Bart.