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I clearly don't want such an interface in >> DMA-buf at all. >> >> You can do that as private iommufd interface, e.g. where iommufd >> offers the functionality to say give me PFNs if you want that. > > I'm not sure what a "private" interface means if VFIO and DRM/RDMA > drivers need to implement the exporter side? That's not exactly > private if it in so many drivers. > > I've tried to make the importer side private, if you have better ideas > how to make it more private please share them. > >> But when there is a DMA-buf interface even if it is limited to >> iommufd then others will want that as well and that is not something >> we should do again. > > You can say no, that's the point of the export symbol restriciton. > >> Even for iommufd I think we don't need that. What iommufd does is >> basically manipulating a specific IOMMU address space. So the >> interface should be to give that address space to DMA-buf and say >> hey please map you backing store at this address into this address >> space. > > Isn't that pretty much exactly what this series is? Aren't you > splitting hairs to say an "address space" requesting physical is OK > but a "mapping type" requesting physical is not? The net result is > exactly the same, physical addresess flow from exporter to importer. > To be clear, there is no way, nor should there be a way, to use the > DMA API to create a reliable dma_addr_t that is 1:1 with phys_addr_t. Mhm, that sounds like what I wanted to say wasn't understood. > Can you be more specific please, I still have no idea what you are > thinking in terms of an acceptable implementation. Let me try to describe it differently: The iommufd deals with iommu_domain structures which userspace can map different things into. So of hand I would say that an interface to map DMA-buf into such an iommu_domain should look something like this: dma_buf_map_attachment_iommu(struct dma_buf_attachment *attachment, struct iommu_domain *domain, unsigned long iova, unsigned long offset, size_t size, ...); The DMA buf exporter then maps the its data into the iommu_domain at iova starting with offset from within the buffer and size number of bytes. Regards, Christian. > > Jason