Re: [PATCH v6 02/15] net: generalise net_iov chunk owners

[Christoph Hellwig <hch@infradead.org>]

On Wed, Oct 23, 2024 at 03:34:53PM +0100, Pavel Begunkov wrote:
> It doesn't care much what kind of memory it is, nor it's important
> for internals how it's imported, it's user addresses -> pages for
> user convenience sake. All the net_iov setup code is in the page pool
> core code. What it does, however, is implementing the user API, so

That's not what this series does.  It adds the new memory_provider_ops
set of hooks, with once implementation for dmabufs, and one for
io_uring zero copy.

So you are precluding zero copy RX into anything but your magic
io_uring buffers, and using an odd abstraction for that.

The right way would be to support zero copy RX into every
designated dmabuf, and make io_uring work with udmabuf or if
absolutely needed it's own kind of dmabuf.  Instead we create
a maze of incompatible abstractions here.  The use case of e.g.
doing zero copy receive into a NVMe CMB using PCIe P2P transactions
is every but made up, so this does create a problem.