linux-kernel - Re: [RFC v2 01/11] file: add callback for pre-mapping dmabuf

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Message-ID: <20251204131025.GA26860@lst.de>
Date: Thu, 4 Dec 2025 14:10:25 +0100
From: Christoph Hellwig <hch@....de>
To: Christian König <christian.koenig@....com>
Cc: Christoph Hellwig <hch@....de>, Pavel Begunkov <asml.silence@...il.com>,
	linux-block@...r.kernel.org, io-uring@...r.kernel.org,
	Vishal Verma <vishal1.verma@...el.com>, tushar.gohad@...el.com,
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [RFC v2 01/11] file: add callback for pre-mapping dmabuf

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