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
48 lines
2.3 KiB
Markdown
48 lines
2.3 KiB
Markdown
---
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name: schunix-dirsiz-14
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description: DIRSIZ was 14 and truncated silently; raised to 30 on 2026-08-09 by holding the HTree bucket at 256 bytes.
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metadata:
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type: project
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---
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Found 2026-08-09 while staging fonts. `DIRSIZ` in `include/fs/fs.h` is **14**, an
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xv6 inheritance, and the v1 filesystem truncates to it **silently**.
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`JetBrainsMono-Regular.ttf` was stored as `JetBrainsMono-`. Two consequences,
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the second much worse than the first:
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- The file cannot be opened by its real name, and `stat` fails on it — `ls -l`
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showed `?` for every field, which is what tipped this off.
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- **`JetBrainsMono-Regular.ttf` and `JetBrainsMono-Bold.ttf` both truncate to
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`JetBrainsMono-`.** Any set of files sharing a 14-character prefix collides.
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That is silent data loss, not a display limitation.
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## Fixed the same day: DIRSIZ is 30
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**The trick that made it safe: hold the HTree bucket at 256 bytes.**
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The directory hash tree is laid out in *bytes*, not entries. A bucket was 16
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slots x 16 bytes = 256, and `HASHRANGE`, `OVERFLOW_DIR_START` (113 * BSIZE),
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`OVERFLOW_DIR_END` and `MAXFSIZE` are all derived from that. Raising DIRSIZ
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naively to 62 would have made buckets 1024 bytes and pushed the primary area
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from 117 KB to 470 KB, straight through the overflow region -- silent corruption
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of every directory.
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DIRSIZ 30 makes `struct dirent` exactly **32 bytes**, so a 256-byte bucket holds
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**8** slots instead of 16 and **every byte offset in the layout is unchanged**.
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`DIRENT_BUCKET_BYTES` in `include/fs/fs.h` is now the constant the maths is written
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against; `kernel/fs/fs.c` and `tools/mkfs.c` both use it instead of
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`16 * sizeof(struct dirent)`. Cost: more overflow use in heavily collided
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directories.
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**Verified in the running system**: `/usr/share/fonts` lists
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`JetBrainsMono-Regular.ttf` in full, and `/tmp/JetBrainsMono-Regular.txt` and
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`/tmp/JetBrainsMono-Bold.txt` coexist with distinct contents -- the exact case
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that used to collapse into one entry. All four bootcheck modes pass.
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**Still not POSIX's 255.** Getting there means reshaping the directory format,
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which wants the on-disk version policy SchFS is getting first. 30 covers real
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filenames; it is not a general solution.
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`sysroot/bin`'s 244 toybox links were checked for collisions at the old limit:
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there were none, so nothing was silently broken before this.
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