bpo-39640: os.fdatasync: fall back to fsync() on POSIX systems withou…

[gmelikov]

…t fdatasync() support

POSIX fdatasync() is similar to fsync() but it tries not to sync non-needed
metadata. If POSIX OS doesn't have it - it's safe to use fsync()
(If we need to sync data to disk - we have to use one of these functions).

This change helps to run code with fdatasync() on MacOS without fallbacks
in Python code.

That it's a usual practice:

• https://github.com/libuv/libuv/pull/1580/files/bdd987a9b4347164e31e22d2d5ce06fbb5ebc859
• https://rev.ng/gitlab/revng/qemu/commit/6f1953c4c14566d3303709869fd26201828b3ccf

Signed-off-by: George Melikov mail@gmelikov.ru

https://bugs.python.org/issue39640

[the-knights-who-say-ni]

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[gmelikov]

Don't know why bot thinks that CLA not signed, I've signed it.

[codecov]

Codecov Report

Merging #18516 into master will increase coverage by 1.08%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master   #18516       +/-   ##
===========================================
+ Coverage   82.11%   83.20%    +1.08%     
===========================================
  Files        1955     1571      -384     
  Lines      588856   414730   -174126     
  Branches    44427    44456       +29     
===========================================
- Hits       483559   345065   -138494     
+ Misses      95647    60019    -35628     
+ Partials     9650     9646        -4     

Impacted Files	Coverage Δ
Lib/distutils/tests/test_bdist_rpm.py	30.00% <0.00%> (-65.00%)	⬇️
Lib/distutils/command/bdist_rpm.py	7.63% <0.00%> (-56.88%)	⬇️
Lib/test/test_urllib2net.py	76.92% <0.00%> (-13.85%)	⬇️
Lib/test/test_smtpnet.py	78.57% <0.00%> (-7.15%)	⬇️
Lib/ftplib.py	63.85% <0.00%> (-6.06%)	⬇️
Lib/test/test_ftplib.py	87.11% <0.00%> (-4.72%)	⬇️
Tools/scripts/db2pickle.py	17.82% <0.00%> (-3.97%)	⬇️
Tools/scripts/pickle2db.py	16.98% <0.00%> (-3.78%)	⬇️
Lib/test/test_socket.py	71.94% <0.00%> (-3.77%)	⬇️
Lib/distutils/tests/test_bdist_msi.py	56.25% <0.00%> (-3.75%)	⬇️
... and 469 more

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[brettcannon]

@gmelikov this is being flagged as unsigned because you have changes made to the PR by a user named "gmelikov-mcs" which has not signed the CLA.

[gmelikov]

@brettcannon ah, my bad! Thank you, fixed and rebased.

[gmelikov]

Rebased and ready to review.

[encukou]

I'm not familiar with MacOS, so I don't feel comfortable merging this – especially without tests.

Tagging Ronald, who is working on macOS and might be or know the right person to review this.

[hugovk]

Closing as @gpshead rejected https://bugs.python.org/issue39640 on 2022-03-20:

The os module provides a pretty low level simple shim over platform APIs. It is better for logic like this to live in a higher level application library rather than make big assumptions on the part of the user.

try:
    os.fdatasync(fd)
except Exception as err:
    logging.debug("fdatasync(fd) failed %s, falling back to fsync(fd)", err)
    os.fsync(fd)