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

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Message-ID: <20251204110709.GA22971@lst.de>
Date: Thu, 4 Dec 2025 12:07:09 +0100
From: Christoph Hellwig <hch@....de>
To: Christian König <christian.koenig@....com>
Cc: 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>, Christoph Hellwig <hch@....de>,
	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 11:46:45AM +0100, Christian König wrote:
> On 11/23/25 23:51, Pavel Begunkov wrote:
> > Add a file callback that maps a dmabuf for the given file and returns
> > an opaque token of type struct dma_token representing the mapping.
> 
> I'm really scratching my head what you mean with that?
> 
> And why the heck would we need to pass a DMA-buf to a struct file?

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.