| Filename | Latest commit message | Latest commit date |
|---|---|---|
c874811679
A fresh boot spent 2600 ms in schinit's bootstrap() before printing its first
line, and the whole of it was device nodes. Measured rather than guessed: an
instrumented bootstrap reported 2600 ms on a fresh image and 0 ms on the next
boot, because the nodes already existed by then and mknod failed fast. The cost
was therefore invisible to anyone not building images -- which is to say,
invisible to everyone except whoever works on this.
Each node was a real inode on the root filesystem, and SchFS commits every
mutation as its own transaction group: a copy-on-write rewrite of the path to
the root, then an uberblock behind a cache flush. Twenty of those is seconds.
The duplication mattered more than the time. Major and minor numbers are the
kernel's -- devsw[] in kernel/dev/cdev.c is what they dispatch on -- and schinit
held a second copy of that mapping with nothing checking the two agreed. Adding
a character device meant editing a userspace program, and a wrong minor produced
a node that opened successfully and did nothing.
kernel/fs/devfs.c puts the table next to the thing it describes and serves /dev
behind the same fs_ops vtable procfs uses. The namespace is all it provides:
fileread and filewrite see T_DEV and go through devsw themselves, so a read
never reaches it. It is read-only, and dirlink and ialloc answer EROFS rather
than pretending -- a node exists because the kernel has the device, or it does
not exist.
This also makes /proc/filesystems true. It has advertised "nodev devtmpfs" for
as long as it has existed, against a kernel that had no such filesystem.
Two things found while measuring what remained:
* The thirteen mknod() calls for /proc ran *after* the procfs mount, so every
one was resolving a path into a read-only synthetic filesystem and failing.
procfs.c's own note called them a fallback to be cleaned up later; they have
been dead for longer than that.
* The four mkdir() calls for mount points were the rest of it. They are made
by the image builder now (sysroot-install), and the ones in init are a
fallback -- a mkdir that fails because the directory exists costs a path
walk and no writes, where creating one costs a transaction.
bootstrap() is now 0 ms on a fresh image, down from 2600.
init opens /dev/console after the mount rather than mknod'ing a node called
"console" into the root directory, which is what used to leave a stray /console
in `ls /`. The old path is kept as a fallback: if the mount fails there is no
/dev/console and no way to report it.
socktest passes, /proc still lists per-process directories, ps -e still
enumerates.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
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| .. | ||
| boot.md | ||
| devices.md | ||
| filesystem.md | ||
| graphics.md | ||
| init.md | ||
| kernel.md | ||
| networking.md | ||
| README.md | ||
| schfs.md | ||
| syscalls.md | ||
| usb.md | ||
The system, layer by layer
What SchOS is today. Everything in this directory is built and running; what is merely intended lives in ../plan/.
The names, and what each one covers
uname -s reports SchIFT, the way every Unix reports its kernel rather than
its distribution.
| Layer | Name | What it is |
|---|---|---|
| System | SchOS | The distribution — kernel, userland, tooling |
| Kernel | SchIFT | Multi-core x86-64 kernel with a modular VFS |
| Filesystem | SchFS | Transactional, copy-on-write, the root filesystem |
| API | SchAPI | The native programming interface — designed, not built |
| Compositor | Schcom | Owns the display; v0 runs |
The stack, bottom to top
┌─────────────────────────────────────────────────┐
│ toybox mksh musl first-party cmd/ │ userland
├─────────────────────────────────────────────────┤
│ schinit — PID 1, job manifests, supervision │
├─────────────────────────────────────────────────┤
│ syscall table — Linux numbering, one .inc file │ ← the ABI seam
╞═════════════════════════════════════════════════╡
│ VFS │ sockets │ signals │ mmap │ poll │ procfs │
├──────┴─────────┴─────────┴──────┴──────┴────────┤
│ SchFS │ lwIP │ text/gfx │ buffer cache │
├─────────┴────────┴────────────┴─────────────────┤
│ device model — class vtables, bus binding │
├─────────────────────────────────────────────────┤
│ drivers: xHCI e1000 virtio-gpu VBE IDE PS/2│
├─────────────────────────────────────────────────┤
│ scheduler │ paging │ traps │ IRQ │ SMP │ DMA │ SchIFT core
└─────────────────────────────────────────────────┘
▲
UEFI loader (boot/uefi)
The two seams that matter are the syscall table and the device model. Above the first, software is ordinary and portable — musl and toybox are unmodified. Below the second, a driver never names its consumer and a consumer never names a driver.
Where it came from
SchOS began as xv6 and is now mostly something else. What survives from xv6 is the shape of the process table, the sleep/wakeup discipline, and the buffer cache. What has been replaced: the scheduler and trap path (rewritten for x86-64 and for more than one processor), the memory manager, the entire filesystem, the syscall layer, and every driver.
That inheritance is worth knowing when reading the code, because the parts that still look like xv6 follow xv6's conventions and the parts that do not, do not.
The documents
Read in this order if you are new:
| boot.md | Firmware to the first userspace process. The shortest path through the whole system. |
| kernel.md | Memory, processes, scheduling, traps, signals, SMP. |
| syscalls.md | The one table everything is generated from, and how a musl binary runs unmodified. |
| filesystem.md | The VFS, the buffer cache, mounts, procfs. |
| schfs.md | The copy-on-write root filesystem. |
| devices.md | Buses, classes, binding, and the vtables consumers talk to. |
| usb.md | xHCI, the USB core, and the three class drivers. |
| graphics.md | Framebuffer, text rendering, the console, and PSOGM. |
| networking.md | NIC drivers, lwIP, and both socket families. |
| init.md | schinit and the job manifests. |
Three rules that hold across all of it
The kernel and the host tools compile the same SchFS source. mkschfs
cannot disagree with the kernel about the on-disk format, because there is only
one implementation. Format bugs are found on the host, where a test takes a
second instead of a boot.
Syscalls are declared in exactly one place. kernel/sys/table.inc.
The constants, the dispatch table and the Linux translation map are all
generated from it, so a syscall cannot be half-registered.
A list you can read beats a list assembled by side effects. Drivers are
written out by hand in kernel/drivers/registry.c rather than collected by a
linker section, and platform devices are registered in one function rather than
inside each driver's init. The tradeoff is deliberate: self-registration is
nicer to write, and it means the list of what is in your kernel is not written
down anywhere you can read.