gh-132742: Refactor fcntl.fcntl() and fcntl.ioctl()

[serhiy-storchaka]

• Support arbitrary bytes-like objects, not only bytes, in fcntl().
• The fcntl() buffer argument is now null-terminated.
• Automatically retry an ioctl() system calls failing with EINTR.
• Release the GIL for an ioctl() system call even for large bytes-like object.
• Do not silence arbitrary errors whet try to get a buffer.
• Optimize argument parsing, check the argument type before trying to get a buffer or convert it to integer.
• Fix some error messages.

• Issue: Rewrite the fcntl module #132742

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📚 Documentation preview 📚: https://cpython-previews--132768.org.readthedocs.build/

[serhiy-storchaka]

@vstinner, could you please take a look?

Other changes are planned for other PRs.

[vstinner]

There are many indentation levels (nested if), did you consider to split this code into sub-functions?

[vstinner]

LGTM

[serhiy-storchaka]

Thank you for your review, @vstinner.

I just tried to split the code on smaller functions. This adds many duplications: declarations of local variables ret, async_err, buf, functions parameters (there is a subtle difference for fcntl and ioct, it is easy to make an error). While there is a benefit if such refactoring (the conditions for types can be simpler), but there is also an additional risk of introducing errors, and the code will be larger. So I am not sure that the net effect is positive.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows Server 2022 NoGIL 3.x (tier-1) has failed when building commit 9f5994b.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1241/builds/5397) and take a look at the build logs.
4. Check if the failure is related to this commit (9f5994b) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1241/builds/5397

Failed tests:

• test_opcache

Summary of the results of the build (if available):

==

Click to see traceback logs

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remote: Total 14 (delta 12), reused 2 (delta 0), pack-reused 0 (from 0)        
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HEAD is now at 9f5994b94cb gh-132742: Refactor fcntl.fcntl() and fcntl.ioctl()  (GH-132768)
Switched to and reset branch 'main'

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