netdev - Re: [PATCH vhost v11 05/10] virtio_ring: introduce virtqueue_dma

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Date: Thu, 20 Jul 2023 14:45:14 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Christoph Hellwig <hch@...radead.org>,
 virtualization@...ts.linux-foundation.org,
 Jason Wang <jasowang@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>,
 netdev@...r.kernel.org,
 bpf@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH vhost v11 05/10] virtio_ring: introduce virtqueue_dma_dev()

On Wed, 19 Jul 2023 23:22:42 -0700, Christoph Hellwig <hch@...radead.org> wrote:
> On Thu, Jul 13, 2023 at 10:51:59AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Jul 13, 2023 at 04:15:16AM -0700, Christoph Hellwig wrote:
> > > On Mon, Jul 10, 2023 at 11:42:32AM +0800, Xuan Zhuo wrote:
> > > > Added virtqueue_dma_dev() to get DMA device for virtio. Then the
> > > > caller can do dma operation in advance. The purpose is to keep memory
> > > > mapped across multiple add/get buf operations.
> > >
> > > This is just poking holes into the abstraction..
> >
> > More specifically?
>
> Because now you expose a device that can't be used for the non-dma
> mapping case and shoud be hidden.

 Sorry I can not got.

 virtqueue_dma_dev() return the device that working with the DMA APIs.
 Then that can be used like other devices. So what is the problem.

 I always think the code path without the DMA APIs is the trouble for you.

 Thanks.