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Nexoniarz 3034efd300 net: a frame wakes the stack, instead of waiting for the clock

The network thread waited on the timer and nothing else, so a frame that landed
just after a poll sat in the ring for up to 10 ms -- the largest fixed latency in
the system. That was deliberate when the stack was new (a receive path woken by
an interrupt is much harder to debug than one that is asked) and there is now a
working stack to compare against, which is exactly when it becomes safe to do.

The frame is still *pulled* by the thread through .receive. It has to be: a call
into lwIP can reach the driver, the driver can sleep on the buffer cache, and an
interrupt handler may do neither. netdev_rx_signal() delivers nothing and reads
no ring -- it only ends the wait early.

The wait stays on the timer tick rather than moving to a channel of its own, and
that is the design. lwIP's timers must still run when the link is silent, so the
clock has to remain a floor under the wait, and sleep() cannot wait on two things
at once. Joining the tick's existing wakeup costs nothing and leaves one wait
with one predicate.

rx_signal lives under tickslock for the same reason it gets no lock of its own:
sleep() releases tickslock atomically, so a driver setting the flag and waking
under that lock cannot lose the wakeup by arriving between the predicate test and
the sleep. A private lock would not be held across the sleep, and that window
would be back. Calling it from interrupt context is safe on the same terms the
timer handler already relies on -- acquire() disables interrupts, so a CPU
holding tickslock cannot be interrupted into it.

The e1000 signals on RXT0 (a frame or burst has landed) and RXDMT0 (the ring has
fallen below its threshold, which is when waiting for the clock hurts most).

Measured rather than asserted: /proc/netif reports wake_rx and wake_tick, and
across three pings rx_frames and wake_rx both went 2 -> 6 -- every received frame
woke the thread through the interrupt. wake_tick keeps advancing as the idle
floor, which is what lwIP's timers need. socktest still passes and ping is still
0% loss.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2

2026-09-12 17:23:46 +02:00

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Roadmap — everything else still open

The three current decisions have their own documents; see README.md. This file holds what is left: work that is scoped, agreed and unstarted, with nothing in it that is finished.

Finished work is not here. It moved to ../architecture/ and was rewritten as a description of what it produced — see the rule. What used to be phases 1 through 4 of this file, several hundred lines of ticked boxes, is now usb, networking.md, graphics.md and devices.md over there.

1. Storage and the boot path

Make a USB disk mountable and bootable. The xHCI stack, the bulk-only transport, the SCSI layer and the block device all work — a superblock reads back through bread(). What is missing is that the root device is compiled in rather than selectable, so nothing can be told to mount it.

This is also the first piece of the installer, and it is the single change that would most enlarge what SchOS can boot from.

2. Graphics

A /dev/dri-style device with mode setting, so resolution stops being whatever the loader asked for. Worth doing with hybrid.md's GPU eviction rather than before it — moving the driver out is what makes a modeset API affordable to design properly.
Double buffering and vblank. display_ops specifies both and no driver implements either. Schcom needs both to not tear.
Port the console onto the text layer and delete the cell grid. The layer exists, the rasteriser exists, and the console still indexes font_data[256][16].
Load a font from disk and point the console at it.
CFF/Type 2 charstrings, so OTF fonts work. A separate font_ops provider and a bytecode interpreter, not an extension of the glyf path.
Text layout — advance widths, kerning — as a library in lib/, so the terminal and the file manager are not each solving it.

The console keeps its fixed grid until the first item above; proportional text belongs to the GUI.

3. Networking

Three things the stack owed on the day it landed, all still owed:

accept() does not report the peer's address, and there is no getsockname/getpeername. Nothing has needed them yet; a server that wants to log who connected will.
No routing table. With two interfaces up, the first is the default route and the second is reachable only by an address on its own subnet. That is a rule rather than an accident, and it is not routing.

setsockopt returning 0 for everything is in foundations.md instead, because the Wayland work needs it.

4. The interactive crash screen

PSOGM renders and stops. The idea is a small OS inside the crash, and the framing decides the design:

At panic time the kernel is the only thing running, which is exactly why it can offer what a live system cannot: walk the stack, read another process's memory, dump page tables, inspect the process table — with no scheduler and no locking to respect, because nothing else can race you.

What makes it a system rather than a print statement is that it keeps the base machine's drivers. Concretely, the ones that work with interrupts off: the framebuffer (gfx_draw_pixel is a plain memory write), the PS/2 keyboard (pollable via ports 0x60/0x64), and the serial port. Those three are a complete console.

Everything else — IDE, USB, the timer, anything that sleeps or takes a sleeplock — is off limits, because the lock it needs may be precisely the one held by the CPU that just died.

So the shape is a polled event loop over preallocated state: no kalloc, no sleep/wakeup, no acquire on anything a live path might hold, one static command buffer, and that driver set. That restriction is not a limitation to work around later; it is the invariant that makes the mode trustworthy when everything else is not. Anything wanting more should be answered by rebooting into a recovery environment.

A useful precedent to read but not copy: DDB, the BSD in-kernel debugger, is exactly this, and its hard-won rule is the same one — a debugger that can deadlock is worse than no debugger.

5. The installer and `.sip`

Scoped in projects/schinst/README.md, which holds the detail. In short:

.sip format specification, written down before any code
tools/mksip — capture a directory tree into a package
The apply path
An installation environment that boots from the ISO, partitions, applies the .sip, and installs the loader

.sip is modelled on WIM, and the thing worth copying from WIM is that it is file-based, not block-based: one file holds a whole filesystem, applies to a partition of any size, and several images can share their common files.

Most of this already exists. tools/mkschfs.c and tools/mkfs.c both do content dedup with an (st_dev, st_ino) fast path, and SchFS's B-tree is content addressed. mksip should share that code rather than reimplement it — that is the reason the dedup was factored the way it was.

Open questions, all wanting a decision before code:

Compression. Something with a small decompressor is worth more than something with a good ratio, because the decompressor runs in the installation environment.
Multiple images per .sip — WIM's real trick, install/recovery/boot sharing one blob store. Worth the complexity now, or not?
Can the kernel mount a .sip read-only directly? It is close to a filesystem already, and if it can, the installation environment's root can simply be the .sip.

The GUI for this is a Wayland client; see wayland.md.

6. SchFS beyond SchOS

In the order they should happen.

~~An on-disk format version~~, and an upgrade path. The version policy is done — see ../architecture/schfs.md. What remains is the upgrade step, and it cannot be written until there are two formats to convert between; the first bump is when that becomes real work rather than speculation.

The format is now pinned, which is what the other two items were waiting on.

A Linux implementation, FUSE first. Three reasons in order of weight: it can be tested with fsx and xfstests, which are far harsher than anything written alongside the code; it carries no licence entanglement, since libfuse is LGPL and used across a process boundary; and it can reuse the read/write logic already in tools/mkschfs and tools/schfs_fsck rather than being written twice and having the two disagree.

A kernel module is a different project, comes only after FUSE passes xfstests, and carries the licence problem ../licensing.md describes.

The missing features, listed honestly before adding any: no journal replay across an unclean shutdown beyond what copy-on-write gives for free, no snapshots, no sparse-file support, and no online fsck. Snapshots are the one where the existing design already pays for most of the cost — the B-tree is copy-on-write, which is most of the machinery; nothing takes or names a snapshot.

7. The kernel's own gaps

Not phases, and each one improves everything above it:

A slab or pool allocator. kalloc hands out one page at a time, and every subsystem written since has invented its own fixed-size table to work around that. This is the single change that would most improve the rest of the kernel.
A page cache, which is what a general writable MAP_SHARED needs. foundations.md delivers a memfd instead, which is narrower and sufficient for the GUI.
Symlinks in procfs, so /proc/<pid>/exe can be one and ps -o comm stops printing [init]. Belongs with the rest of the VFS work rather than on its own.
The ls -lR hang. Heavy directory listing across many commands in one long shell session eventually makes a later, unrelated directory hang; the same command succeeds on a fresh boot. Not inode or file table exhaustion — both fail cleanly and neither fired. Next step: instrument itable/ftable occupancy across a long session and watch what climbs.

Kept out of scope on purpose

Anything that needs pushing or publishing. This work stays local.
TrueType hinting.
XWayland.

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