mmap/VM snapshot question

I have four processes accessing the same file using mmap() with MAP_SHARED.
I'd like to take a copy-on-write snapshot of that file so that I can do a
backup. However, if I try to start a fifth process and map the file with
MAP_PRIVATE, the copy-on-write only works one way; i.e. changes made by the
other processes can be visible by the backup process.

How do you get the Linux VM to reverse the copy-on-write, where the four
original processes can keep sharing their data and the fifth backup process
retains the data made at the time of the snapshot?

Thanks,
 -Byron

--
Byron Stanoszek                         Ph: (330) 644-3059
Systems Programmer                      Fax: (330) 644-8110
Commercial Timesharing Inc.             Email: [email protected]
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