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Old 03-24-2009, 08:30 AM   #1
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Help needed: mmap and physical memory access

Hi All,

For some testing purpose I need to use mmap having file descriptor received out of /dev/mem. But, I have no idea about what offset I should use. It would certainly be very helpful if someone could suggest as what offset should I use. The required (desired) length is 1MB.
And, system I am using is FC9.

Manav Swargiary
Old 03-24-2009, 05:08 PM   #2
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Based on the mmap man page: "offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE)."

For sysconf itself see 'man sysconf'. The suggested solution is:

#include <unistd.h>
offset = sysconf(_SC_PAGE_SIZE);

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Last edited by JaksoDebr; 04-02-2009 at 05:06 AM.
Old 03-24-2009, 11:43 PM   #3
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I will read and try out this solution. Thanks a lot.

Old 03-25-2009, 03:38 AM   #4
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offset = sysconf(_SC_PAGE_SIZE);

This does not return the offset, instead it returns the size of a page.
I need a portion of a physical memory (preferably 1 MB) which is unused and can be accessed from user space using mmap. Offset (relative to base address) should point to an unused physical memory segment.


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