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Date: Mon, 21 Jul 2025 09:50:53 +0200
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@meta.com>
Cc: linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, hch@lst.de,
	axboe@kernel.dk, leonro@nvidia.com, Keith Busch <kbusch@kernel.org>
Subject: Re: [PATCHv2 7/7] nvme: convert metadata mapping to dma iter
Message-ID: <20250721075053.GH32034@lst.de>
References: <20250720184040.2402790-1-kbusch@meta.com> <20250720184040.2402790-8-kbusch@meta.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

> +	if (!blk_rq_integrity_dma_map_iter_start(req, dev->dev,
> +						&iod->meta_dma_state, &iter))

Do the normal two-tab indent here to make this a bit more readable?

>  	if (entries == 1) {
> -		nvme_pci_sgl_set_data_sg(sg_list, sgl);
> +		iod->meta_total_len = iter.len;
> +		nvme_pci_sgl_set_data(sg_list, &iter);
> +		iod->nr_meta_descriptors = 0;

This should probably just set up the linear metadata pointer instead
of a single-segment SGL.

> +	if (!iod->nr_meta_descriptors) {
> +		dma_unmap_page(dma_dev, le64_to_cpu(sg_list->addr),
> +				le32_to_cpu(sg_list->length), dir);
> +		return;
> +	}
> +
> +	for (i = 1; i <= iod->nr_meta_descriptors; i++)
> +		dma_unmap_page(dma_dev, le64_to_cpu(sg_list[i].addr),
> +				le32_to_cpu(sg_list[i].length), dir);
> +}

The use of nr_meta_descriptors is still incorrect here.  nr_descriptors
counts the number of descriptors we got from the dma pools, which
currently is always 1 for metadata SGLs.  The length of the SGL
descriptor simplify comes from le32_to_cpu(sg_list[0].length) divided
by the sgl entry size.