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Date: Wed, 21 Jan 2026 10:05:08 +0100
From: Christoph Hellwig <hch@lst.de>
To: Chuck Lever <cel@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>, Leon Romanovsky <leon@kernel.org>,
	Christoph Hellwig <hch@lst.de>, NeilBrown <neilb@ownmail.net>,
	Jeff Layton <jlayton@kernel.org>,
	Olga Kornievskaia <okorniev@redhat.com>,
	Dai Ngo <dai.ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
	linux-rdma@vger.kernel.org, linux-nfs@vger.kernel.org,
	Chuck Lever <chuck.lever@oracle.com>
Subject: Re: [PATCH v2 3/4] RDMA/core: add MR support for bvec-based RDMA
 operations
Message-ID: <20260121090508.GE16458@lst.de>
References: <20260120143124.1822121-1-cel@kernel.org> <20260120143124.1822121-4-cel@kernel.org>
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In-Reply-To: <20260120143124.1822121-4-cel@kernel.org>
User-Agent: Mutt/1.5.17 (2007-11-01)

> +static int rdma_rw_init_mr_wrs_bvec(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
> +		u32 port_num, const struct bio_vec *bvec, u32 nr_bvec,
> +		u32 offset, u64 remote_addr, u32 rkey,
> +		enum dma_data_direction dir)

Any reason this is not using the bvec_iter like the other paths?

Yhe mapping to the scatterlist would then basically be a much
simplified version of __blk_rq_map_sg.

> +		dma_addr = ib_dma_map_bvec(dev, bv, dir);
> +		if (ib_dma_mapping_error(dev, dma_addr)) {
> +			ret = -ENOMEM;
> +			goto out_unmap;
> +		}
> +
> +		/* sg_set_page() initializes the entry; ib_map_mr_sg() uses
> +		 * only sg_dma_address/len, ignoring the page pointer.
> +		 */
> +		sg_set_page(&sgl[i], bv->bv_page, len, bv->bv_offset);
> +		sg_dma_address(&sgl[i]) = dma_addr;
> +		sg_dma_len(&sgl[i]) = len;

And once we have a scatterlist, this should probably just use
ib_dma_map_sg* ?  And maybe rdma_rw_init_one_mr?

> +	/*
> +	 * For bvec MR path: store synthetic scatterlist with DMA addresses
> +	 * for cleanup. Only valid when type == RDMA_RW_MR and initialized
> +	 * via rdma_rw_ctx_init_bvec().
> +	 */
> +	struct scatterlist	*mr_sgl;
> +	u32			mr_sg_cnt;
>  };

This probably should be in the reg union arm and thus the separate
allocatiom?