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Date: Thu, 15 Jan 2026 16:58:56 +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>, linux-rdma@vger.kernel.org,
	linux-nfs@vger.kernel.org, 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>,
	Chuck Lever <chuck.lever@oracle.com>
Subject: Re: [PATCH v1 3/4] RDMA/core: add MR support for bvec-based RDMA
 operations
Message-ID: <20260115155856.GD14083@lst.de>
References: <20260114143948.3946615-1-cel@kernel.org> <20260114143948.3946615-4-cel@kernel.org>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Wed, Jan 14, 2026 at 09:39:47AM -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> The bvec-based RDMA API currently returns -EOPNOTSUPP when Memory
> Region registration is required. This prevents iWARP devices from
> using the bvec path, since iWARP requires MR registration for RDMA
> READ operations. The force_mr debug parameter is also unusable with
> bvec input.
> 
> Add rdma_rw_init_mr_wrs_bvec() to handle MR registration for bvec
> arrays. The approach creates a synthetic scatterlist populated with
> DMA addresses from the bvecs, then reuses the existing ib_map_mr_sg()
> infrastructure. This avoids driver changes while keeping the
> implementation small.
> 
> The synthetic scatterlist is stored in the rdma_rw_ctx for cleanup.
> On destroy, the MRs are returned to the pool and the bvec DMA
> mappings are released using the stored addresses.

I wish we'd just have a bvec based MR API, and could use that.
But I don't want to hold this work back, because of that.