Issue 3517: PATCH - Providing fullfsync on supported platforms

Python currently provides os.fsync to call the POSIX 'fsync' on
platforms that support it.  While this function forces the operating
system to force a file buffer to the storage device, data may still be
waiting in the hardware write buffers on the storage device.  Certain
platforms (so far, only OS X) provide "fullfsync" [1] to request that
storage devices flush their write buffers to the actual physical media.  

This functionality is especially useful to VCS and DB developers, and
already appears in SQLite [2] and MySQL [3], amongst others.

This patch includes code changes to Modules/posixmodule.c that exposes
os.fullfsync on supported platforms, including the appropriate
documentation added to Doc/library/os.rst

-Ian Charnas

[1] Discussion of fsync and fullfsync on darwin platform:
http://lists.apple.com/archives/darwin-dev/2005/Feb/msg00072.html

[2] SQLite uses fullfsync on all platforms that define it:
http://www.sqlite.org/cvstrac/fileview?f=sqlite/src/os_unix.c

[3] MySQL uses fullfsync only on the darwin platform and only when
F_FULLFSYNC is defined as 51, which seems to be short-sighted in that
this symbol may change value in future versions of OS X.  To see this
code, download a mysql 5.x source snapshot and open up
mysql-<version-number>/innobase/os/os0file.c

I'm sorry to have lead you this way, but since there is no fullfsync()
system call, IMO you should just make the F_FULLFSYNC constant
available.  That should go into fcntlmodule.c.

Sounds fair enough.  I was looking forward to the glitz and glamor of
the os module, but I'll settle for a good seat in fcntl.  Here's a patch
implementing just that.

-ian

Thanks, checked into the trunk as r65581.