---
name: schunix-devfs-procfs
description: "How /dev and /proc work in Schunix; ps and top work as of 2026-08-08"
metadata: 
  node_type: memory
  type: project
  originSessionId: a665e14b-86bd-4b41-a228-51377f3e9225
  modified: 2026-08-08T16:24:48.813Z
---

**/dev** nodes are created by `cmd/init/main.c` with `mknod()` at every boot,
and served by `kernel/dev/cdev.c`'s `devsw[major]` table. Minor numbers under
major 1 follow Linux's mem-major layout where free: null=2, zero=5, full=7,
random=8, urandom=9. `/dev/hole` (minor 4) was deleted 2026-08-01 — an
abandoned experiment nothing referenced.

**/proc** (`kernel/dev/procfs.c`, major 6) synthesises eight global files:
meminfo, uptime, cpuinfo, version, stat, loadavg, mounts, filesystems. Each is
a device node with its own minor; reading renders the whole text and returns
the slice at the caller's offset.

**Two gotchas that shaped it:**

1. `devsw[].read()` used to be called as `read(ip, 1, addr, n)` — every caller
   passed the literal `1` where an offset belongs, so a device could never
   know where a read started. Fine for a stream like the console, fatal for a
   /proc file: without an offset every read returns the whole text again and
   `cat` never terminates. `kernel/fs/file.c` now passes `f->off` and advances
   it by the amount returned.

2. `/proc/mounts` must list `/` **last**. df keeps the last mount point that
   prefixes the path it was asked about, so listing root first made `df /`
   report /proc's numbers.

**Per-process `/proc/<pid>/` directories now exist and `ps`/`top` work** —
re-verified 2026-08-08 with `tools/bootcheck.ps1 -Ps`: ps finds init and the
shell, `-o ppid` shows the real parent, top reads `/proc/meminfo`. This entry
used to say they were impossible without a VFS rewrite; that was overtaken by
`kernel/fs/procfs.c`, which implements /proc as a real filesystem behind
`struct fs_ops` with synthetic inodes (`pid<<8` encoding) rather than touching
`fs.c`. See [[schfs-phase3-writes]] for the `fs_ops` dispatch.

One cosmetic gap remains: `ps -o comm` shows `[init]` in brackets, because
toybox `readlink()`s `/proc/<pid>/exe` and ours is a regular file, not a
symlink. Needs symlink support in procfs.

`sysinfo(2)` also reports real memory now (`PHYSTOP` and
`kalloc_free_bytes()`); it used to return hardcoded 256MB/128MB, which is what
`free` reads.