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| Filename | Latest commit message | Latest commit date |
|---|---|---|
42f98130c4
docs/plan/ldls.md milestone L3c. ldls/kpi/ implements 41 of 8139too's 94
symbols rather than logging them: register access to a mapped BAR, the PCI
calls to /dev/pci, allocation to mmap and PCIIOC_DMA, register_netdev to
/dev/netdev.
# ldlsd /lib/modules/8139too.ko /lib/modules/btf
found 10ec:8139 at 00:05.0
bar 1 0x0000000081060000 256 mem
calling probe, with 41 of 94 symbols implemented
kpi: mapped BAR 1 -- phys 0x0000000081060000, 256 bytes
kpi: the driver read a MAC off the hardware: 52:54:00🆎cd:ef
netuser: ldls0 is a process now, 52:54:0🆎cd:ef
probe returned 0 after 0 stub call(s)
52:54:00🆎cd:ef is what the machine was configured with. Nothing invented
it: the driver bit-banged the card's EEPROM, serially, through a BAR mapped by
/dev/pci, and handed back what it found. That it matches means the loader, the
relocations, the BTF offsets, the BAR mapping and the register accessors are
all correct at once, which is why it was the thing to aim at. Zero stub calls:
every symbol probe reaches is implemented.
Two bugs, one of them the kernel's.
Mine first: pci_iomap checked a failed mmap for -1 only, while SchOS returns
-errno. It returned -13 as a pointer, the driver took that as its register
base, and the first write landed at 0x4e -- thirteen below where it meant to
be.
Underneath it, the real one. sys_mmap rounds a length up to a page, the only
granularity an MMU has, and pciuser_mmio_ok() compared that against the BAR's
own size. rtl8139's registers are 256 bytes, the request became 4096, and the
answer was -EACCES for a device the process legitimately held. A BAR smaller
than a page could never be mapped at all, and nothing had noticed because the
only consumer until now was virtio-gpu, whose BARs are large. The check is now
against the pages the BAR lies in, and the widening is named where it happens:
a sub-page BAR hands over the whole page, forced by the hardware rather than
chosen.
That is exactly what hybrid.md said a foreign driver would be good for --
"what it asks for is what a foreign driver would ask for too" -- arriving as a
concrete bug rather than a prediction.
kpi_io_ok() now bounds every ioread/iowrite against the mapping pci_iomap
returned. A stray access would otherwise be a page fault with no context, and
with no IOMMU a hosted driver's wild writes have to be caught early or not at
all. It is also what turned the fault above into two lines naming the offsets.
Not done, and said so in the output rather than only in the doc: no frame has
moved. ndo_open is never called and there is no transmit or receive path, so
ldlsd releases the interface instead of leaving it up -- a link that reports
itself up with nothing draining its queue is a black hole, and the stack would
send DHCP into it for ever. Down is the true answer until packets move. That
is L3d, now listed separately.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
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| cmd | ||
| docs | ||
| etc | ||
| include | ||
| kernel | ||
| ldls | ||
| lib | ||
| ports | ||
| projects | ||
| tools | ||
| .gdbinit | ||
| .gitattributes | ||
| .gitignore | ||
| LICENSE | ||
| LICENSE.MIT | ||
| Makefile | ||
| NOTICE | ||
| README.md | ||
| run.ps1 | ||
| shell.nix | ||
A 64-bit operating system, written from the metal up.
SMP · copy-on-write filesystem · TCP/IP · PCI, USB and virtio drivers · TrueType text · Linux syscall ABI
SchOS began as xv6 and is now mostly something else. The scheduler, the memory manager and the trap path have been rewritten for x86-64 and for more than one processor; the filesystem has been replaced outright; the syscall table speaks Linux numbering so that real software — musl, toybox, mksh — runs unmodified.
It is a hobby system built by one person, and it is honest about that: what works below has been run, not inferred, and the gaps are listed as plainly as the features.
The pieces
| 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 | System programming interface — the stable surface |
| Compositor | SchCom | Display compositor (planned) |
| Window manager | SchWM | (planned) |
| Desktop | SchDE | (planned) |
uname -s reports SchIFT, the way every Unix reports its kernel rather than
its distribution.
What works
Kernel — Long mode, 4-level paging, preemptive multitasking. SMP: one, two and four processors all boot, with CPU enumeration from the ACPI MADT rather than the 1994 MP table. Memory sized from the E820 map, so it runs in tens of megabytes rather than demanding hundreds.
Filesystem — SchFS is the root: a copy-on-write B-tree with a
uberblock ring, so a crash leaves either the old tree or the new one and there
is nothing to repair. Free space is derived from the tree rather than stored
beside it, which removes a whole class of disagreement. /proc/schfs shows the
generation counter advancing as writes commit.
Processes — fork, exec, wait, pipes, signals, sessions and process groups,
mmap (anonymous and file-backed), POSIX shared memory, Unix domain sockets,
poll.
Devices — PCI enumeration with a bus-agnostic device model at
/proc/devices. Drivers for e1000 networking, virtio-gpu and stdvga
displays, xHCI USB with HID, hub and mass-storage class drivers, IDE, PS/2,
serial. /dev/fb0 speaks the Linux fbdev interface.
Networking — ARP, IPv4, ICMP, UDP, TCP and DHCP, on lwIP behind a driver-agnostic interface class. Verified end to end from the host, both directions, rather than by inspection.
Userland — musl, toybox and mksh, built from source. ls, cat, ps,
top, wc, cp, mount and the rest behave the way you expect, because they
are the real programs.
Text — a TrueType rasteriser (glyf outlines, composite glyphs, cmap
format 4) replacing the 8×16 cell grid. JetBrains Mono for the terminal, Roboto
for the desktop layer to come.
When it dies — PSOGM, the Purple Screen of Guru Meditation: stop code, fault address, call chain, and a QR code containing a text copy of the whole report.
Quick start
make # kernel + UEFI loader + root filesystem
make qemu # build it and boot it
make iso # a bootable ISO for VMware or real hardware
Builds on Linux, macOS, FreeBSD/OpenBSD/NetBSD and Windows (Git Bash). The toolchain is clang + lld everywhere — it is a cross-compiler by construction, so one LLVM install targets the bare-metal kernel, the 16-bit boot code and musl userland from any host. See docs/guides/building.md for prerequisites per platform, and docs/history/moving-to-linux.md for moving a checkout between machines.
Testing
Booting to a prompt proves nothing: a filesystem can mount and still fail the first real command, and that has happened here. So the test harness drives the serial console and asserts on what comes back.
tools/windows/bootcheck.ps1 # boot, run real commands, check the answers
tools/windows/bootcheck.ps1 -Tty -Ps # terminal behaviour, process enumeration
make schfs-check # SchFS B-tree, object and image suites
bootcheck is PowerShell because pwsh runs on every supported host.
Layout
kernel/ arch/ core/ dev/ drivers/ fs/ net/ proc/ sys/
fs/schfs/ the filesystem -- same source the host tools compile
include/ kernel and userland headers
boot/ uefi/ (PE loader) common/ (shared loader UI)
lib/ cmd/ first-party userland runtime and programs
ports/ third-party software built from source
tools/ windows/ (.ps1) posix/ (.sh) python/ (.py) and .c/.pl
docs/ architecture/ (what it is) plan/ (what's next)
guides/ (how to work on it) history/ (why it's like this)
docs/README.md is the index. If you are reading the tree for the first time, docs/architecture/README.md is the system layer by layer.
One rule worth knowing: 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 — found and fixed on the host, where a
test takes a second instead of a boot.
Another: syscalls are declared in exactly one place,
kernel/sys/table.inc. Everything else is generated from it.
Not there yet
- No desktop. Schcom composites and routes input; the plan is now to put it on Wayland and delete the homegrown protocol. See docs/plan/wayland.md.
- No descriptor passing. No
sendmsg/recvmsg, so noSCM_RIGHTS— which is what the GUI work stops at. docs/plan/foundations.md. - No dynamic linking.
exechandles staticET_EXEConly. - No page cache, so writable
MAP_SHAREDof a file is refused rather than faked. - A USB disk cannot be booted from — the root device is compiled in rather than selectable.
- SchFS has no Linux driver yet; the plan is on-disk format version first, then FUSE, then a kernel module.
- CFF/OpenType outlines and TrueType hinting are deliberately out of scope.
Licensing
Apache-2.0, copyright Nexoniarz. See LICENSE.
The kernel derives from xv6, which is MIT — see LICENSE.MIT. Third-party code redistributed in a built image (musl, toybox, mksh, the fonts) keeps its own licence; NOTICE carries the attributions.
Drivers may be adapted from BSD sources, which are compatible. Linux drivers are not: GPL-2.0-only and Apache-2.0 cannot be combined and redistributed. Reading Linux to understand hardware is fine; translating a driver is not. Best of all is the public specification — xHCI, virtio, AHCI, e1000 — which carries no licence on what you write from it.