Mapping Kernel Virtual Memory

Mapping Kernel Virtual Memory

You can use mmap() to create a segment that is a window on the kernel's virtual address space. To do so you create a file descriptor by opening the special file /dev/mmem (note the double "m"). For more information, see the mem(7) (single "m") reference page.

The acceptable off and len values you can use when mapping /dev/mmem are defined by the contents of /var/sysgen/master.d/mem. Normally this file restricts possible mappings to specific hardware registers such as the high-precision clock. For an example of mapping /dev/mmem, see the example code in the syssgi(2) reference page under the SGI_QUERY_CYCLECNTR argument.