Re: [PATCH v1 1/4] RDMA/core: add bio_vec based RDMA read/write API

[Christoph Hellwig <hch@lst.de>]

> +static int rdma_rw_init_single_wr_bvec(struct rdma_rw_ctx *ctx,
> +		struct ib_qp *qp, const struct bio_vec *bvec, u32 offset,
> +		u64 remote_addr, u32 rkey, enum dma_data_direction dir)
> +{
> +	struct ib_device *dev = qp->pd->device;
> +	struct ib_rdma_wr *rdma_wr = &ctx->single.wr;
> +	struct bio_vec adjusted = *bvec;
> +	u64 dma_addr;
> +
> +	ctx->nr_ops = 1;
> +
> +	if (offset) {
> +		adjusted.bv_offset += offset;
> +		adjusted.bv_len -= offset;
> +	}

Hmm, if we need to split/adjust bvecs, it might be better to
pass a bvec_iter and let the iter handle the iteration?

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

Much of this seems to duplicate rdma_rw_init_map_wrs.  I wonder if
having a low-level helper that gets either a scatterlist or bvec array
(or bvec_iter) and just has different inner loops for them would
make more sense?  If not we'll just need to migrate everyone off
the scatterlist version ASAP :)