Re: [LSF/MM/BPF TOPIC] dmabuf backed read/write

Jason Gunthorpe
2026-02-09T14:02:13Z

On Mon, Feb 09, 2026 at 02:55:26PM +0100, Christian König wrote:

> Yeah, that is basically what everybody currently does with out of tree code.

:\

> The problem is that this requires internal knowledge of the exported
> buffer and how the I/O path is using it.

Well here I am saying the buffer has a P2P struct page so that is all
you actually need to know. It just follows the existing proven path in
the IO stack.

> So to generalize this for upstreaming it would need something like a
> giant whitelist of exporter/importer combinations which are known to
> work together and not crash the kernel in surprising and hard to
> track down ways.

Well I think the mapping type proposal goes a long way toward dealing
wiht this problem. Let's shelve the discussion until after we discuss
that with patches.

> > Reworking the block stack to not rely on page is also a good path, but
> > probably alot harder. :\
>
> Yeah, that would be really really nice to have and the latest
> patches for extending the struct file stuff actually looked quite
> promising.

Yeah, I thought the dma token through the IO stack looked very
interesting too. I hope it eventually succeeds!

Jason