@gpshead This PR introduces 4 new functions which are simple wrappers. The rationale is explained in the main comment, and other details including testing instructions are provided as inline comments on the diffs.

For now I have converted#101832 and#101833 to drafts since they require more work and are slightly more ambitious projects.

As always, no rush.

@gpshead as a reviewer of the preceedinggh-101831.

@erlend-aasland Thank you for being patient.

Turns out that unlike unlikeopenpty(),login_tty(), andforkpty(), these 4 POSIX functions are a part of the standard C library on *nix and not a part oflibutil. Therefore, I just needed to add the function names in anAC_CHECK_FUNCS block inconfigure.ac.

However, maybe we need to make a separate PR to modify theopenpty(),login_tty(),forkpty() block inconfigure.ac to useWITH_SAVE_ENV?

[…] Therefore, I just needed to add the function names in an AC_CHECK_FUNCS block in configure.ac.

Much better, thanks! There is no need forWITH_SAVE_ENV now, AFAICS.

The configure.ac changes look good to me. I'll leave the rest of the review for@zware and@gpshead who've been active on the issue and previous PRs.

@erlend-aasland Thank you!

@gpshead Just a gentle reminder. No rush.

🤖 New build scheduled with the buildbot fleet by@gpshead for commitf6dcd54 🤖

If you want to schedule another build, you need to add the🔨 test-with-buildbots label again.

Reading the manpages further, I see that Linux has a reentrant variant ofptsname:

ptsname_r() is a Linux extension, that is proposed for inclusion in the next major revision of POSIX.1 (Issue 8).

IMO,os.ptsname should call this on Linux if it's available (with achar buffer[MAXPATHLEN+1]), and the docs should note that the function isn't thread-safe on other systems.

(If you prefer to leaveptsname_r to another PR, that's an option too.)

@encukou I prefer to includeptsname_r in this PR; thank you for the suggestion and sorry about the late reply. This is on my TODO list; please give me 1 more day (or maybe 2).

There's no rush, take your time :)

@encukou

I have made the changes you requested and more; please take a look at them when you get time:

1. Changeos.grantpt() so that the correcterrno is set before callingposix_error().
2. Changeos.ptsname() so that it usesos.ptsname_r() when available; reflect this in docs.
3. MentionOS_CLOEXEC in the documentation foros.posix_openpt().
4. Mention in the docs that these functions do not close the master fd upon failure.
5. One of the tests that you added was usingos.openpty() followed byos.grantpt() andos.unlockpt(). That did not make sense to me, since I thinkopenpty() C implementations do this already? Please let me know if this is wrong. I added a new test that follows the standard sequenceposix_openpt() -> grantpt() -> unlockpt() -> ptsname() that this new test subsumed test that you had written forptsname().
6. I usedhttps://github.com/tiran/cpython_autoconf (autoconf version 2.71) written by@tiran to generate the configure script. The testTests / Check if generated files are up to date (pull_request) failed; maybe I should use something else now? The default autoconf on my Debian system is also (GNU Autoconf) 2.71, so generating using that will not make a difference I think.
7. About the pty pair terminology: I noticed that you used the naming schememain, second. I used the alternativemother, son as a test to see if you like it. While I am not a CPython maintainer and hence do not have much say in deciding which directions such a prestigious project should take, I have severe clinical OCD/OCPD and would like to issue a warning here: using generic names likemain_fd, second_fd, orparent_fd, child_fd, orserver_fd, client_fdwill lead to havoc very easily. Just take a look at the source of your very ownhttps://github.com/python/cpython/blob/3.12/Lib/pty.py and try a search/replace involving terms parent/child (already used by processes) or a program likessh(1) which uses the terms server/client in networking context and also sets up a pty pair. On the other hand one can easily havefirst_fd, second_fd, third_fd or evenmain_fd in their existing programs. The pairmain, subordinate comes to mind, but again,main_fd might be taken andmain, subordinate carry the same overtones asmaster, slave, which is what you are trying to avoid in the first place. For the most comfortable change, we must use something that is -
   • not already taken to almost absolutely eliminate any chances of collision while
   • maintaining that the initialsm ands stay the same.

Edit: while this is not the focus of this PR, about point 7 above, I have generated some data using grep on the cpython repository and added it here:#85984 (comment) (commenting again for better reach).

Edit: Sorry about the obsessive spam; I cannot help myself, I have OCD. Before taking a break from this, I would like to finally point out that a pty is a pair offiles and not a pair offds. Therefore, if we call themmain file/main end andsecond file/second end, then in code the corresponding terms might bemain_fd andsecond_fd. That is misleading: a file can be addressed via multiple fds and upon reopening thesecond file/second end, we should call the new fdthird_fd orsecond_fd_of_second_end and notreopened_second_fd (since you open files and not file descriptors).

ON THE OTHER HAND:main end andsecondARY end might be better. I still think we should grep for all possible terms to avoid collision.

1-4. Thank you!
5. Thanks. I'm not an expert here -- I'm learning about ptys and their C API as I go. I'm happy that the test I added is hackable :)
6. The command ismake regen-configure. If that doesn't work for you, run theubuntu:22.04 container (that is currently what the makefile uses, via/Tools/build/regen-configure.sh). If it's a problem, let me know and I'll regenerate this.
If you found@tiran's outdated container mentioned in somecurrent documentation, please let me know -- we should fix that. (Sadly we can't fix all the docs, like personal notes or shell histories...)
7. For the tests, local variable names don't matter much; it's OK to be a bit creative. For the API, this addsfd -- no problem there! For docs, it'smaster/slave for now; changing that will be a different discussion (in which theEditorial board might well decide to keep following POSIX).

Let's pretendsecond_fd stands forfd of the second file, andreopened_second_fd stands forfd for the reopened second file, orreopened fd for the second file. Does that work better? If not, change this to whatever feels best :)

@encukou you are very kind. Let me work on the reconfigure (and everything else you suggested).

@encukou Looks like all checks have passed! Your/Tools/build/regen-configure.sh suggestion worked like a charm... after I moved myself away from a directory that had colons (:) in its name as a time (hr, min, sec) separator;docker does not seem to like that.

@encukou Thank you for merging this! Looks like finally after years I have all the prerequisites for#101833. That one now needs to be updated andmaybe broken up into a few parts in case it becomes too difficult to review: one for signal handling, one for winsize handling, one for adjusting the tests, etc. I will do this sometime during the next few months.

Thank you for perservering!
Looks like the main thing missing in 101833 is tests, so, a good strategy might be to send a PR whenever you get a test working :)

If I happen to miss a notification (= I don't reply for about a week), please ping me again.

@encukou

Looks like the main thing missing in 101833 is tests

The tests for that were my first contribution to CPython in 2020. However, I still need to update the tests to use the various robust functions that I have added toos,termios, andtty over the years instead of the ad-hoc ones that I wrote inLib/test/test_pty.py. If additional tests are required, I will definitely add them if you wish :)