site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com What's the equivalent of Linux's kmap to map a user virtual address into the kernel memory space so that it is accessible "magically" (i.e. without any additional mapping/unmapping required) to all other tasks and kernel threads? man fcntl <http://lwn.net/Articles/111226/> -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... On Mar 6, 2007, at 4:35 PM, Bhavesh Davda wrote: I've already looked at vm_map and AFAICT, that ain't it. The concept of kmap() is specifically for split kernel and user virtual address spaces, with both a limit on the total of the two together (a 1G/3G split is common for Linux and BSD systems), and a limit on the visibility of physical memory over the 4G mark to a 32 bit kernel with a 4G limit on virtual address space, on a machine with

4G of physical RAM. In other words, it's a generic bounce buffer mechanism utilizing memory mapping windows to relocate so-called "high memory" into the kernel virtual address space so that the kernel can see it. It's unlikely that you will need to worry yourself with this sort of thing. In general, this is taken care of either by uio or by the IOMemoryDescriptor construct, which pretty much amount to the same thing. If the reason you are asking is that you are trying to find a kmap()- like mechanism to avoid polluting the VM/buffer cache with pages that you plan to use once and throw away clean (i.e. you are trying to write a streaming video server or something else that wants to move a lot of data, and since it isn't going to look at it again, it doesn't want to keep it around taking up space), then you should look at: and look at F_NOCACHE to disable caching of the data in the kernel by the unified buffer cache subsystem.

If the reason you are asking is that you want to abuse the ability to map user space pages into the kernel virtual address space, an IOMemoryDescriptor will let you do this, in combination with the "map" member function, but I would discourage that, just like the Linux guys discourage using kmap() that way: This email sent to site_archiver@lists.apple.com