[RFC v2 01/11] file: add callback for pre-mapping dmabuf

[Christoph Hellwig]

On Thu, Jan 08, 2026 at 10:19:18AM +0800, Ming Lei wrote:
> > The feature is in no way nvme specific.  nvme is just the initial
> > underlying driver.  It makes total sense to support this for any high
> > performance block device, and to pass it through file systems.
> 
> But why does FS care the dma buffer attachment? Since high performance
> host controller is exactly the dma buffer attachment point.

I can't parse what you're trying to say here.

> If the callback is added in `struct file_operations` for wiring dma buffer
> and the importer(host contrller), you will see it is hard to let it cross device
> mapper/raid or other stackable block devices.

Why?

But even when not stacking, the registration still needs to go
through the file system even for a single device, never mind multiple
controlled by the file system.