bpo-31106: Fix handling of erros in posix_fallocate() (#3000)

[socketpair]

https://bugs.python.org/issue31106

[socketpair]

@nirs I confused. Should I fix anything in code ? Seems everything is right according to our conversation.

[socketpair]

@Mariatta @larryhastings
Please review

[socketpair]

ping

[larryhastings]

Thanks for the patch! I'd like just a few small changes.

I understand why you just assign to errno the way you did, but I think we can do a little better. Instead, please change the "errno == EINTR" to "result == EINTR" in both functions, and only assign to errno immediately before calling posix_error(). (It's reasonable to assign to errno there because of how posix_error() works.)

Note that we can safely assign to errno outside ALLOW_THREADS, because errno is per-thread (using amazing magic).

I wish I knew why these functions don't assign to errno...!

[bedevere-bot]

A Python core developer, larryhastings, has requested some changes be
made to your pull request before we can consider merging it. If you
could please address their requests along with any other requests in
other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment
on this pull request containing the phrase I didn't expect the Spanish Inquisition!
I will then notify larryhastings along with any other core developers
who have left a review that you're ready for them to take another look
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[larryhastings]

That's a big improvement. Thanks for the patch, and the cleanup!

[miss-islington]

Thanks @socketpair for the PR, and @larryhastings for merging it 🌮🎉.. I'm working now to backport this PR to: 3.6.
🐍🍒⛏🤖

[bedevere-bot]

GH-4101 is a backport of this pull request to the 3.6 branch.