linux-kernel - Re: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file

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Message-ID: <aE-qxK6rbvfoeBr6@infradead.org>
Date: Sun, 15 Jun 2025 22:25:24 -0700
From: Christoph Hellwig <hch@...radead.org>
To: wangtao <tao.wangtao@...or.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	Christian König <christian.koenig@....com>,
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	hanfeng 00012985 <feng.han@...or.com>
Subject: Re: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file_range

On Fri, Jun 13, 2025 at 09:33:55AM +0000, wangtao wrote:
> 
> > 
> > On Mon, Jun 09, 2025 at 09:32:20AM +0000, wangtao wrote:
> > > Are you suggesting adding an ITER_DMABUF type to iov_iter,
> > 
> > Yes.
> 
> May I clarify: Do all disk operations require data to pass through
> memory (reading into memory or writing from memory)? In the block layer,
> the bio structure uses bio_iov_iter_get_pages to convert iter_type
> objects into memory-backed bio_vec representations.
> However, some dmabufs are not memory-based, making page-to-bio_vec
> conversion impossible. This suggests adding a callback function in
> dma_buf_ops to handle dmabuf- to-bio_vec conversion.

bios do support PCI P2P tranfers.  This could be fairly easily extended
to other peer to peer transfers if we manage to come up with a coherent
model for them.  No need for a callback.