Implement mkfifo with directory descriptor support - #9056

Current revision

Targets Python 3.15 main with one logical commit: 5b251a5fecda927d37fcc238887362328c5c40b5, based on f39da82d9d38cd5bdceb9e645205e830f65126fb.

Rebased once to include the merged shared I/O CI fix and intervening main changes. The unique patch has identical added/deleted lines and an unchanged range-diff; original author and assistance trailer are preserved. No Lib/ changes. Main's TextIOWrapper setter fix and this PR's FileIO open/EINTR changes are both preserved. Normal commit hooks, explicit changed-range hooks, and whitespace/source checks passed. No new local build or runtime test is claimed. Normal hosted CI on this exact head is pending; earlier validation below remains historical.

Summary

Extract the independent POSIX os.mkfifo implementation from #8954 (43065e79ddc46eafeca58cb39398ac007b5d25f7) for the Python 3.15 target.

• Create FIFOs through the host layer, release interpreter execution during the syscall, and retry interrupted calls after checking signals.
• Support dir_fd with truthful capability reporting. Keep descriptors as raw C integers so absolute paths can correctly ignore negative descriptors without manufacturing an invalid borrowed descriptor.
• Resolve Apple's newer mkfifoat symbol at runtime, preserving ordinary mkfifo on older systems.
• Adapt the mega hunk with local path/mode converters and precise descriptor overflow messages.
• Retry EINTR in direct-path FileIO and os.open calls, honoring signal-handler exceptions. Enabling mkfifo exposes the previously skipped canonical FIFO-open cases. os.open carries directory descriptors as raw integers through a narrow host openat wrapper, without creating a Rust descriptor borrow across callbacks. Generic DirFd conversion and custom FileIO openers are unchanged.

Duplicate review found no separate mkfifo implementation. #9054 changes chmod in the same files but owns different behavior. No changes from that open PR are required.

References: CPython 3.14.7 implementation and argument parser.

Initial mkfifo validation (96df674)

• Normal repository hooks passed.
• VM/host-layer Clippy and separately configured CAPI Clippy passed with -D warnings.
• Native build passed. The focused new function in the existing stdlib_os.py snippet passed; the baseline fails with missing os.mkfifo before any filesystem operation.
• All 27 bounded reference/native cases match CPython 3.14.7, including path/mode/descriptor conversion order, huge-integer bounds, absolute negative descriptors, errors without filenames, and warnings-as-errors before creation.
• Unchanged canonical PosixTester.test_mkfifo and TestPosixDirFd.test_mkfifo_dir_fd both passed in a private temporary working directory.
• All behavior checks are Python-side. Tests only create, stat and unlink FIFOs in owned temporary directories; they never open a FIFO, change umask, create devices, or target user/system paths.

EINTR follow-up validation

The initial hosted run failed both newly enabled canonical FIFO-open tests. The same failures reproduced locally in 0.26 seconds; they are not flaky-test skips. The fix follows CPython 3.14 FileIO retry handling and os.open retry handling, with a raw directory-descriptor boundary instead of mega's borrowed-descriptor lifetime across signal callbacks.

Validated follow-up commit cadfd738f5e5ef6d38cf3e63b9a4573f41eaea6e:

• Independent raw-descriptor lifetime/ownership review and normal hooks passed.
• Native build, VM/host Clippy, and separately configured CAPI Clippy passed with -D warnings.
• Both previously failing canonical FIFO-open tests pass unchanged in 1.27 seconds, in a private temporary directory with an external hard timeout and subprocess cleanup. These tests intentionally open only their own FIFOs.
• Five additional unchanged canonical tests pass: mkfifo, mkfifo dir_fd, open dir_fd, FileIO seek/tell, and FileIO attributes.
• Native checks match exact CPython 3.14.7/3.14.8 for raising signal handlers in FileIO/open/openat, non-EINTR filename errors, single invocation of a failing custom opener, the public signature, valid index conversion order, str/bytes paths, and the None directory-descriptor default.
• No invalid/closed-descriptor probes or canonical test edits are part of this follow-up.

Fresh hosted CI is required; the original-head EINTR failure is superseded only after the new head is validated.

Scope and remaining limitations

Android retains ordinary mkfifo but no dir_fd because the pinned libc crate has no Android mkfifoat binding. Redox remains excluded; Windows/WASI modules are unchanged. Apple ABI and availability were source-reviewed, but non-Linux runtime execution was not performed. The existing shared path converter still differs from CPython in the prefix of the error for an invalid __fspath__ return; its behavior was not duplicated or broadly rewritten here.

Full stdlib_os.py, full workspace tests, and the complete canonical OS suite were not run locally; they include unrelated operations outside this bounded validation. Hosted CI remains required. No canonical assertions or skips were weakened, and no Rust behavior tests were added.

Summary by CodeRabbit

• New Features
  • Added os.mkfifo for creating named pipes, with support for paths, permissions, and directory descriptors where available.
  • Added directory-descriptor support to os.open on supported platforms.
  • Updated Python compatibility to 3.15.
• Bug Fixes
  • File-opening operations now retry when interrupted, while still checking for pending signals.
  • Improved handling of negative timestamps on Windows and integer-like values in logarithm and sleep operations.
  • Corrected behavior for memory-mapped searches, struct format errors, and AST constructor validation.