readme.filelocking

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Version 4.9.7 Release Notes

FILE I/O and LOCKING CODE
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The file i/o locking code has been audited. All code was changed to
update files by opening the orignal file in read only mode, unless
it is the first time, then create it. Then open a temp file with
a .pid extension. Make all the changes to the temp file. Then use
the rename(2) function call to automically move the new file over
the old file. This is similar to how some qmail file modification
is done.

No read locks are requested for read only i/o.

Write locks are requested for modify i/o.

To reduce the locking load on the file system, a lock is
not requested for the .dir-control file. If we miss counting
a user during a simulatious user addition, it's not the
end of the world. The number of user entry in that file
is not meant to be exact. It is more of a guide line on
how to spread out user directories across the vpopmail 
3 level user directory tree.

This should reduce the over all file i/o synchronicity 
requirements. And hence reduce the possiblity of lost
file data (like loosing a complete vpasswd user file!!!)

At least we are using the more reliable rename(2) function.