On 03.07.25 16:23, Christoph Hellwig wrote: > [Note: it would be really useful to Cc all relevant maintainers] > > On Fri, Jun 27, 2025 at 04:10:27PM +0100, Pavel Begunkov wrote: >> This series implements it for read/write io_uring requests. The uAPI >> looks similar to normal registered buffers, the user will need to >> register a dmabuf in io_uring first and then use it as any other >> registered buffer. On registration the user also specifies a file >> to map the dmabuf for. > > Just commenting from the in-kernel POV here, where the interface > feels wrong. > > You can't just expose 'the DMA device' up file operations, because > there can be and often is more than one. Similarly stuffing a > dma_addr_t into an iovec is rather dangerous. > > The model that should work much better is to have file operations > to attach to / detach from a dma_buf, and then have an iter that > specifies a dmabuf and offsets into. That way the code behind the > file operations can forward the attachment to all the needed > devices (including more/less while it remains attached to the file) > and can pick the right dma address for each device. > > I also remember some discussion that new dma-buf importers should > use the dynamic imported model for long-term imports, but as I'm > everything but an expert in that area I'll let the dma-buf folks > speak.
Completely correct. As long as you don't have a really good explanation and some mechanism to prevent abuse long term pinning of DMA-bufs should be avoided. Regards, Christian.
