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

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Message-ID: <34c2dbc06d074ffbb8f920418636bafc@honor.com>
Date: Fri, 13 Jun 2025 09:33:55 +0000
From: wangtao <tao.wangtao@...or.com>
To: Christoph Hellwig <hch@...radead.org>
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	<liulu.liu@...or.com>, hanfeng 00012985 <feng.han@...or.com>
Subject: RE: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file_range


> 
> 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.

Interestingly, if such a callback exists, the need for a dedicated
ITER_DMABUF type might disappear. Would you like to discuss potential
implementation tradeoffs here?

Regards,
Wangtao.