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Date: Tue, 21 May 2024 19:38:50 +0530
From: Nitesh Shetty <nj.shetty@samsung.com>
To: Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>, Alasdair
	Kergon <agk@redhat.com>, Mike Snitzer <snitzer@kernel.org>, Mikulas Patocka
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	<hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>, Chaitanya Kulkarni
	<kch@nvidia.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Christian
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	damien.lemoal@opensource.wdc.com, anuj20.g@samsung.com, joshi.k@samsung.com,
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Subject: Re: [PATCH v20 09/12] dm: Add support for copy offload
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On 21/05/24 09:11AM, Hannes Reinecke wrote:
>On 5/20/24 12:20, Nitesh Shetty wrote:
>>Before enabling copy for dm target, check if underlying devices and
>>dm target support copy. Avoid split happening inside dm target.
>>Fail early if the request needs split, currently splitting copy
>>request is not supported.
>>
>>Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>---
>>@@ -397,6 +397,9 @@ struct dm_target {
>>  	 * bio_set_dev(). NOTE: ideally a target should _not_ need this.
>>  	 */
>>  	bool needs_bio_set_dev:1;
>>+
>>+	/* copy offload is supported */
>>+	bool copy_offload_supported:1;
>>  };
>>  void *dm_per_bio_data(struct bio *bio, size_t data_size);
>
>Errm. Not sure this will work. DM tables might be arbitrarily, 
>requiring us to _split_ the copy offload request according to the 
>underlying component devices. But we explicitly disallowed a split in 
>one of the earlier patches.
>Or am I wrong?
>
Yes you are right w.r.to split, we disallow split.
But this flag indicates whether we support copy offload in dm-target or
not. At present we support copy offload only in dm-linear.
For other dm-target, eventhough underlaying device supports copy
offload, dm-target based on it wont support copy offload.
If the present series get merged, we can test and integrate more
targets.

Regards,
Nitesh Shetty

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