Hi, > The pages backing a DMA-buf are not allowed to move (at least not without a > patch set I'm currently working on), but for certain MM operations to work > correctly you must be able to modify the page tables entries and move the > pages backing them around. > > For example try to use fork() with some copy on write pages with this > approach. You will find that you have only two options to correctly handle > this.
The fork() issue should go away with shared memory pages (no cow). I guess this is the reason why vgem is internally backed by shmem. Hmm. So I could try to limit the udmabuf driver to shmem too (i.e. have the ioctl take a shmem filehandle and offset instead of a virtual address). But maybe it is better then to just extend vgem, i.e. add support to create gem objects from existing shmem. Comments? cheers, Gerd
