On 1/4/26 02:42, Ming Lei wrote:

On Thu, Dec 04, 2025 at 02:10:25PM +0100, Christoph Hellwig wrote:

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On Thu, Dec 04, 2025 at 12:09:46PM +0100, Christian König wrote:

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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).

Yeah that would make it much more cleaner.

Also some higher level documentation would certainly help.

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.

Yeah that it might be better if it's more nvme specific came to me as well.

Regards, Christian.

Thanks, Ming