--- Mike DeKoker <mdekoker@yahoo.com> wrote: > > I am developing a module for a PCI device. In order to > get large enough DMA buffers, I am reserving the upper > N megabytes of RAM (via the kernel parameter "mem=") and > using ioremap to get at the buffer from within the kernel. > This is all fine and dandy, I can do DMA transfers > to/from my device just fine. My question is, is it possible > to map this DMA buffer into user space? Normally, the mmap function of a driver validates a few things and sets flags in the vma. Making the pages accessible to users is done in the nopage function. Instead, you can make your driver's mmap function update the process page table also. Since you know the physical address of the reserved memory, you can create and set the PTEs in the page table. When the process tries to access this page, it is alerady there - there is no page fault and the nopage function will not be called. I haven't thought this through fully. You will have to consider how to keep track of multiple mmap's and what to do if the user app exits abnormally. Hope this helps, Ravi. __________________________________ Do you Yahoo!? Yahoo! Calendar - Free online calendar with sync to Outlook(TM). http://calendar.yahoo.com -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
