directio for device memory

["Ameya Mitragotri" <ameya.mitragotri@xxxxxxxxx>]

Hello,
While reading the source for directio in the kernel (2.6.20), i figured that it always uses 'get_user_pages'. Any memory mapped page (marked VM_IO) cannot be directio'ed to the disk.  Is that because device to device DMA is not possible? Is there a mechanism in the kernel by which i can directly write device memory to disk?

Thanks
Ameya