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

[Ming Lei <ming.lei@redhat.com>]

On Thu, Dec 04, 2025 at 02:10:25PM +0100, Christoph Hellwig wrote:
> On Thu, Dec 04, 2025 at 12:09:46PM +0100, Christian König wrote:
> > > I find the naming pretty confusing a well.  But what this does is to
> > > tell the file system/driver that it should expect a future
> > > read_iter/write_iter operation that takes data from / puts data into
> > > the dmabuf passed to this operation.
> > 
> > That explanation makes much more sense.
> > 
> > The remaining question is why does the underlying file system / driver
> > needs to know that it will get addresses from a DMA-buf?
> 
> This eventually ends up calling dma_buf_dynamic_attach and provides
> a way to find the dma_buf_attachment later in the I/O path.

Maybe it can be named as ->dma_buf_attach()?  For wiring dma-buf and the
importer side(nvme).

But I am wondering why not make it as one subsystem interface, such as nvme
ioctl, then the whole implementation can be simplified a lot. It is reasonable
because subsystem is exactly the side for consuming/importing the dma-buf.
 

Thanks, 
Ming