[Retr0G28]

What

fcntl(F_GETFL) on a pipe end reported O_RDONLY for the read end and O_WRONLY for the write end, because the access mode came from the host, where pipe ends are one-way. FreeBSD 11 pipes are bidirectional: kern_pipe opens both ends with finit(..., FREAD | FWRITE, ...) (sys/kern/sys_pipe.c), and kern_fcntl builds F_GETFL from OFLAGS(fp->f_flag) (sys/kern/kern_descrip.c), so both ends report O_RDWR.

The guest descriptor table now marks descriptors created by pipe. The mark follows dup, dup2 and F_DUPFD with the shared status flags, an entry made by open replaces it, and close drops it. F_GETFL reports O_RDWR for a marked descriptor and still asks the host for every other descriptor, so a FIFO opened with O_RDONLY keeps reporting O_RDONLY, as on FreeBSD. The sentence about this gap is cut from the fcntl entry in docs/dev/debt/libkernel.md.

Test changes:

• guest_kernel_fcntl (PipeFlagsRoundTrip) now expects O_RDWR on both ends, with and without O_NONBLOCK, and on an F_DUPFD copy of the write end.
• guest_dup now expects O_RDWR | O_NONBLOCK in its shared-status-flags case.

Tested

Windows 11, WinLibs MinGW-w64 GCC 15.2.0 r7, CMake + Ninja, Release, -DBUILD_TESTING=ON, on main 77e3121.

• Before the fix, guest_kernel_fcntl with the new expectations fails (exit 0xc0000409 from the failed Require). With this PR it passes.
• ctest -R "fcntl|pipe|dup|poll|select|kqueue|stdio|descriptor|socket" -E "^agc_": 40 of 40 pass when run serially.
• Every guest_ test (547): the only failures that remain when run alone are guest_module_dir and guest_module_identity. They fail the same way on main on this machine (Windows Defender blocks a file they generate, WinError 225).
• python tools/check_conventions.py --base origin/main reports no errors. The one warning is the existing length of the fcntl debt entry, which this PR shortens.
• Linux: @xXPBSXx ran the PR head on WSL2 Ubuntu 24.04 (GCC 13.3.0): guest_dup and guest_kernel_fcntl pass, and both fail with main's DescriptorControl and Stdio.cpp (comment below). Not run on bare-metal Linux.
• No title or homebrew run.

Overlap: tools/pr_overlap.py could not compare some open PRs. I checked the ones that touch the same code files (#7121, #6977, #6044, #5021, #6936, #7201, #7530). None changes the access mode F_GETFL reports for a pipe. The rest touch only other lines of docs/dev/debt/libkernel.md.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed under Silent stubs in their library's technical debt file
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• Fixes: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

[github-actions]

Other open pull requests touch the same code. Merging one will break the other, or both implement the same thing. If this one builds on them, list them in Depends on.

Pull request	Conflicting files (lines on main)	Same exports	Same new files
PR 9019	core/libs/prx/libkernel/File/include/DescriptorControl.hpp L15 core/libs/prx/libkernel/File/src/DescriptorControl.cpp L117, L567-568

Some comparisons could not be completed because a pull request conflicts with the base branch. Review these shared files manually before concluding that there is no overlap.

Pull request	Shared files not compared
PR 4630	docs/dev/debt/libkernel.md
PR 5021	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 6044	core/libs/tests/GuestDup.cpp core/libs/tests/GuestKernelFcntl.cpp
PR 6149	docs/dev/debt/libkernel.md
PR 6740	docs/dev/debt/libkernel.md
PR 6830	docs/dev/debt/libkernel.md
PR 6936	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 7049	docs/dev/debt/libkernel.md
PR 7088	docs/dev/debt/libkernel.md
PR 7105	docs/dev/debt/libkernel.md
PR 7121	core/libs/prx/libkernel/File/include/DescriptorControl.hpp core/libs/prx/libkernel/File/src/DescriptorControl.cpp core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 7149	docs/dev/debt/libkernel.md
PR 7201	core/libs/prx/libkernel/File/src/Stdio.cpp
PR 7509	docs/dev/debt/libkernel.md
PR 7565	docs/dev/debt/libkernel.md
PR 7653	docs/dev/debt/libkernel.md
PR 8010	docs/dev/debt/libkernel.md
PR 8520	core/libs/prx/libkernel/File/src/DescriptorControl.cpp core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 8553	docs/dev/debt/libkernel.md
PR 9074	docs/dev/debt/libkernel.md
PR 9133	docs/dev/debt/libkernel.md
PR 9199	docs/dev/debt/libkernel.md
PR 9256	core/libs/prx/libkernel/File/src/DescriptorControl.cpp core/libs/tests/GuestKernelFcntl.cpp docs/dev/debt/libkernel.md
PR 9284	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 9293	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 9297	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 9302	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 9423	core/libs/prx/libkernel/File/src/Stdio.cpp
PR 9557	core/libs/prx/libkernel/File/src/DescriptorControl.cpp docs/dev/debt/libkernel.md
PR 9561	core/libs/prx/libkernel/File/include/DescriptorControl.hpp core/libs/prx/libkernel/File/src/DescriptorControl.cpp core/libs/prx/libkernel/File/src/Stdio.cpp core/libs/tests/GuestKernelFcntl.cpp docs/dev/debt/libkernel.md
PR 9566	core/libs/prx/libkernel/File/include/DescriptorControl.hpp core/libs/prx/libkernel/File/src/DescriptorControl.cpp docs/dev/debt/libkernel.md
PR 9575	docs/dev/debt/libkernel.md
PR 9669	docs/dev/debt/libkernel.md
PR 9693	core/libs/prx/libkernel/File/src/Stdio.cpp docs/dev/debt/libkernel.md
PR 9823	core/libs/prx/libkernel/File/src/Stdio.cpp

[xXPBSXx]

Linux data point for 2d1fa5aea5: WSL2 Ubuntu 24.04 (virtualised kernel, not bare-metal Linux), GCC 13.3.0, Release, BUILD_TESTING=ON, PR head alone (not merged onto main).

• With the PR: ctest -R '^(guest_dup|guest_kernel_fcntl)$' passes 3 of 3 (both tests).
• With DescriptorControl.hpp, DescriptorControl.cpp and Stdio.cpp (libkernel/File) restored to the merge-base (new test cases kept): both fail (Subprocess aborted).
  Not tested: macOS, Windows, a title run.
  AI-assisted (Claude Code).

[DavidSamir]

Hi @Retr0G28, a merge-order note: my #9557 (pipe SIGIO owner) and #9561 (O_FSYNC) edit the same fcntl row of docs/dev/debt/libkernel.md as this PR, and they conflict in that file only. Proposal: no dependency either way; whichever merges second keeps every sentence. Does that work for you? I'll record it in their checklists.

AI-assisted: yes

[Retr0G28]

@DavidSamir Yes, that works for me: no dependency either way, and whichever of us merges second rebases and keeps every sentence of the fcntl row. I checked with git merge-tree: this PR conflicts with #9557 and #9561 only in that row of docs/dev/debt/libkernel.md.