On Wed, Jul 14, 2010 at 10:59:43AM +0900, FUJITA Tomonori wrote: > On Tue, 13 Jul 2010 10:02:23 +0100 > > Zach Pfeffer said this new VCM infrastructure can be useful for > video4linux. However, I don't think we need 3,000-lines another > abstraction layer to solve video4linux's issue nicely. Its only 3000 lines because I haven't converted the code to use function pointers. > I can't find any reasonable reasons that we need to merge VCM; seems > that the combination of the current APIs (or with some small > extensions) can work for the issues that VCM tries to solve. Getting back to the point. There is no API that can handle large buffer allocation and sharing with low-level attribute control for virtual address spaces outside the CPU. At this point if you need to work with big buffers, 1 MB and 16 MB etc, and map those big buffers to non-CPU virtual spaces you need to explicitly carve them out and set up the mappings and sharing by hand. Its reasonable to have an API that can do this especially since IOMMUs are going to become more prevalent. The DMA API et al. take a CPU centric view of virtual space management, sharing has to be explicitly written and external virtual space management is left up to device driver writers. Given a system where each device has an IOMMU or a MMU the whole concept of a scatterlist goes away. The VCM API gets a jump on it. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>