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

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Message-ID: <20230720131928-mutt-send-email-mst@kernel.org>
Date: Thu, 20 Jul 2023 13:21:07 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	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
Subject: Re: [PATCH vhost v11 05/10] virtio_ring: introduce
 virtqueue_dma_dev()

On Wed, Jul 19, 2023 at 11:22:42PM -0700, Christoph Hellwig 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.


Ah, ok.
Well I think we can add wrappers like virtio_dma_sync and so on.
There are NOP for non-dma so passing the dma device is harmless.

-- 
MST