Re: [PATCH v2 1/4] RDMA/core: add bio_vec based RDMA read/write API

[Christoph Hellwig <hch@lst.de>]

On Tue, Jan 20, 2026 at 09:31:21AM -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> The existing rdma_rw_ctx_init() API requires callers to construct a
> scatterlist, which is then DMA-mapped page by page. Callers that
> already have data in bio_vec form (such as the NVMe-oF target) must
> first convert to scatterlist, adding overhead and complexity.
> 
> Introduce rdma_rw_ctx_init_bvec() and rdma_rw_ctx_destroy_bvec() to
> accept bio_vec arrays directly. The new helpers use dma_map_phys()
> for hardware RDMA devices and virtual addressing for software RDMA
> devices (rxe, siw), avoiding intermediate scatterlist construction.
> 
> Memory registration (MR) path support is deferred to a follow-up
> series; callers requiring MR-based transfers (iWARP devices or
> force_mr=1) receive -EOPNOTSUPP and should use the scatterlist API.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  drivers/infiniband/core/rw.c | 210 +++++++++++++++++++++++++++++++++++
>  include/rdma/ib_verbs.h      |  42 +++++++
>  include/rdma/rw.h            |  10 ++
>  3 files changed, 262 insertions(+)
> 
> diff --git a/drivers/infiniband/core/rw.c b/drivers/infiniband/core/rw.c
> index 6354ddf2a274..59f32fecf3df 100644
> --- a/drivers/infiniband/core/rw.c
> +++ b/drivers/infiniband/core/rw.c
> @@ -4,6 +4,7 @@
>   */
>  #include <linux/memremap.h>
>  #include <linux/moduleparam.h>
> +#include <linux/overflow.h>
>  #include <linux/slab.h>
>  #include <linux/pci-p2pdma.h>
>  #include <rdma/mr_pool.h>
> @@ -274,6 +275,111 @@ static int rdma_rw_init_single_wr(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
>  	return 1;
>  }
>  
> +static int rdma_rw_init_single_wr_bvec(struct rdma_rw_ctx *ctx,
> +		struct ib_qp *qp, const struct bio_vec *bvec,

Nit: maybe rename bvec to bvecs or bvec_table to make it clear this
is the base array that the iter operates on?

> +		struct bvec_iter *iter,
> +		u64 remote_addr, u32 rkey, enum dma_data_direction dir)

Nit 2: this can be condensed a little:

> +		struct bvec_iter *iter, u64 remote_addr, u32 rkey,
> +		enum dma_data_direction dir)

> +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,
> +		struct bvec_iter *iter,
> +		u64 remote_addr, u32 rkey, enum dma_data_direction dir)

Same here.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>