Subject: DMA mapping file mappings
To: None <>
From: Damien Bergamini <>
List: tech-kern
Date: 09/14/2004 20:21:49
The title says it all ;-)

I want to map the content of a file into DMA memory. The file 
is mapped into user memory via mmap(2) by a userland tool which 
then send the resulting pointer to a kernel driver via a special 
ioctl. The driver then map the region into DMA using the 
bus_dmamap_load(9) function passing a pointer to the process that 
does the ioctl.
Is it safe to do this? Do I need to call mlock(2) on the file 
mapping or to call mmap(2) with the MAP_WIRED flag before passing 
the pointer to the driver?
Should I copyin(9) everything into kernel memory first?
Thanks for any tip! Tell me if you need more precisions.

Damien Bergamini
damien.bergamini [at]