On Wed, Jan 30, 2019 at 06:26:53PM +0100, Christoph Hellwig wrote: > On Wed, Jan 30, 2019 at 10:55:43AM -0500, Jerome Glisse wrote: > > Even outside GPU driver, device driver like RDMA just want to share their > > doorbell to other device and they do not want to see those doorbell page > > use in direct I/O or anything similar AFAICT. > > At least Mellanox HCA support and inline data feature where you > can copy data directly into the BAR. For something like a usrspace > NVMe target it might be very useful to do direct I/O straight into > the BAR for that. And what i am proposing is not exclusive of that. If exporting device wants to have struct page for its BAR than it can do so. What i do not want is imposing that burden on everyone as many devices do not want or do not care for that. Moreover having struct page and allowing that struct page to trickle know in obscure corner of the kernel means that exporter that want that will also have the burden to check that what they are doing does not end up in something terribly bad. While i would like a one API fits all i do not think that we can sanely do that for P2P. They are too much differences between how different devices expose and manage their BAR to make any such attempt reasonably sane. Maybe thing will evolve oragnicaly, but for now i do not see a way out side the API i am proposing (again this is not exclusive of the struct page API that is upstream both can co-exist and a device can use both or just one). Cheers, Jérôme
