Re: [PATCH v1 3/4] RDMA/core: add MR support for bvec-based RDMA operations

[Leon Romanovsky <leon@kernel.org>]

On Fri, Jan 16, 2026 at 03:50:27PM +0100, Christoph Hellwig wrote:
> On Fri, Jan 16, 2026 at 01:42:36PM +0200, Leon Romanovsky wrote:
> > 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.
> > 
> > I am not very familiar with iWARP. Do you know why we need a special
> > case here? Is there a reason we cannot avoid using scatterlists for
> > iWARP as well, now or in the future?
> 
> iWarp must use MRs for the destination of RDMA READ operations, but the
> core RW code can also optionally use it for other things.  So to support
> that natively here we'd need a bvec-based version of ib_map_mr_sg.  Which
> would be really nice to have for the storage host drivers anyway, but
> until then the scatterlist emulation here can do.  And implementing it
> might take a while, as ib_map_mr_sg is a very thin wrapper around a call
> into the low-level driver.

It is in my roadmap, but as you said, it will take time :(.

Thanks