a1c965da1e
Sixty-five headers sat side by side in include/, so `#include "irq.h"` said nothing about where irq.h was or what it belonged to, and errno.h, stat.h and fcntl.h at the top shadowed the system's for any host tool built with -I./include. They are in folders now -- arch/ core/ fs/ dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and every include names the folder, as Linux's do: "core/proc.h". Done mechanically and checked the hard way: the kernel built from this tree disassembles identically to the one built from the tree before it. The full image boots, and userland is the same set of programs. Paths in docs and comments follow; docs/guides/layout.md has a table of what is where, and tools/fix-includes.py rewrites old-style includes from the folders in the tree, for code written before this. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
37 lines
1.7 KiB
Markdown
37 lines
1.7 KiB
Markdown
---
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name: schunix-linux-open-flags
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description: "include/uapi/fcntl.h must hold Linux's open-flag values — the userland is all Linux-ABI, and a mismatch silently corrupts files"
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metadata:
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node_type: memory
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type: project
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originSessionId: a665e14b-86bd-4b41-a228-51377f3e9225
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modified: 2026-08-03T13:59:19.392Z
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---
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**`include/uapi/fcntl.h` holds Linux x86-64 open-flag values, and must keep holding
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them.** Every program in the userland is built against a libc that sends Linux
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values; the kernel reads them with these constants. Do not "tidy" them into a
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neat sequence — they are an external interface.
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They disagreed until 2026-08-03, and the symptoms looked like filesystem
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corruption rather than a header mistake:
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- Linux `O_APPEND` (0x400) landed on Schunix's `O_TRUNC`, so **`cmd >> file`
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truncated** the file it was supposed to extend.
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- Linux `O_TRUNC` (0x200) landed on `O_CREATE`, so **`cmd > file` did not
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truncate** and left whatever was past the new end in place.
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Found by making `tools/bootcheck.ps1` do ordinary shell work — write a file,
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append to it, `wc -c` the result — instead of only booting to a prompt. The
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byte count was the only thing that said which failure had happened. See
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[[schunix-verify-by-driving-shell]].
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Two related traps fixed at the same time, both worth re-checking after any
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syscall work:
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- `sys_openat` silently dropped `O_TRUNC` and `O_APPEND` while `sys_open`
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honoured both, so the same redirection behaved differently depending on which
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entry point libc called. **Any flag handled in one must be handled in both.**
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- `rmdir` was `NO_LINUX` in `kernel/sys/table.inc`, so every Linux-ABI program
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got ENOSYS. A syscall with no Linux number is unreachable from userland —
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see [[schunix-syscall-single-table]].
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