Subject: Re: [PATCH vhost v11 03/10] virtio_ring: introduce virtqueue_set_premapped()

From: Christoph Hellwig <[email-masked]>
Date: Thu, 13 Jul 2023 04:14:45 -0700

On Mon, Jul 10, 2023 at 11:42:30AM +0800, Xuan Zhuo wrote:
> This helper allows the driver change the dma mode to premapped mode.
> Under the premapped mode, the virtio core do not do dma mapping
> internally.
> 
> This just work when the use_dma_api is true. If the use_dma_api is false,
> the dma options is not through the DMA APIs, that is not the standard
> way of the linux kernel.

I have a hard time parsing this.

More importantly having two modes seems very error prone going down
the route.  If the premapping is so important, why don't we do it
always?