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Date: Thu, 6 Jun 2024 07:56:11 +0200
From: Christoph Hellwig <hch@lst.de>
To: Nitesh Shetty <nj.shetty@samsung.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Jonathan Corbet <corbet@lwn.net>, Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@kernel.org>,
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	Keith Busch <kbusch@kernel.org>, Sagi Grimberg <sagi@grimberg.me>,
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	Alexander Viro <viro@zeniv.linux.org.uk>,
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	hare@suse.de, damien.lemoal@opensource.wdc.com,
	anuj20.g@samsung.com, joshi.k@samsung.com, nitheshshetty@gmail.com,
	gost.dev@samsung.com, linux-block@vger.kernel.org,
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	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v20 03/12] block: add copy offload support
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On Tue, Jun 04, 2024 at 10:50:26AM +0000, Nitesh Shetty wrote:
>>> +	if (!cio)
>>> +		return -ENOMEM;
>>> +	atomic_set(&cio->refcount, 1);
>>> +	cio->waiter = current;
>>> +	cio->endio = endio;
>>> +	cio->private = private;
>>
>> For the main use this could be allocated on-stack.  Is there any good
>> reason to not let callers that really want an async version to implement
>> the async behavior themselves using suitable helpers?
>>
> We cannot do on-stack allocation of cio as we use it in endio handler.
> cio will be used to track partial IO completion as well.
> Callers requiring async implementation would need to manage all this
> bookkeeping themselves, leading to duplication of code. We felt it is
> better to do it here onetime.
> Do you see it any differently ?

We don't really to these async variants for other in-kernel I/O,
so unless we have a really good reason I'd not do here.  The usual
approach is to just have a submission helper for async in-kernel
special bios types, and the let the caller handle the rest.