| Filename | Latest commit message | Latest commit date |
|---|---|---|
a4cfecd19c
"but Virtio GPU is still non functional. it only shows logo" -- and that was a fair reading of it. A second monitor showing a mark for ever is indistinguishable from a second monitor that does not work. The mark was the right answer to the question hybrid.md asked: H2 and H3 needed a screenshot that proved a *userspace process* had drawn something, and that the driver came back after being killed. Both are closed. What was left was a display whose entire output was a logo, on a machine whose console was sitting on the other head. So vgpud mirrors the console onto it. **A copy with a diff.** /dev/fb0 maps the console's framebuffer; the virtio backing store is already mapped, because vgpud allocated it. The backing therefore holds, at all times, exactly what was last sent to the device -- which means it *is* the previous frame, and "what changed" needs no third buffer. Ten times a second: compare rows, skip the ones that match, copy the ones that do not, transfer the one rectangle spanning the rows that changed. Hence present() becoming present_rect(). Moving one line of text through a full-screen transfer of a 1280x800 resource is most of a megabyte of copy for a few hundred bytes of difference, and this loop runs whether or not anything is happening. Mapping /dev/fb0 does not take the screen from the console: the pages are the ones the console draws into, and fb_mapped() only arranges a redraw when the fd is closed. This one never is. Sizes differ, so a head larger than the console centres it on the theme ground the mark already draws, and a smaller head shows the top-left corner -- which is where a terminal puts everything worth seeing. Scaling is the alternative and it is the wrong one; text resampled to a non-integer ratio is text you cannot read. The blocking accept() became poll() with the frame interval as its timeout, because holding the device is no longer the only thing to do. Not the endpoint: a compositor will want this head for itself, and when there is one this goes away. Until then the honest thing for a working display to show is the system that is running on it. **And a bug older than any of it.** schmode reported "cannot reach vgpud on /run/vgpud -- it is not running" about a process that was running perfectly well. Every boot after the first, on any image whose root is writable, and nothing to do with this change -- it reproduces on the previous commit, 3 runs in 4. bind() creates a node at the path, and /run is a directory on the root filesystem rather than a tmpfs. The node outlived the process that bound it and the boot it was bound in, so the next boot's vgpud claimed the device, drew, held it -- and then failed bind() on a name that already existed. A driver nobody could talk to, and an error message naming the wrong cause. It unlinks before binding now, which is what a Unix daemon does. The usual objection, that this lets a second instance steal a live socket, does not apply here: two vgpuds cannot coexist, because the first holds the PCI claim and the second is refused the device long before it reaches bind(). The claim is the mutual exclusion; the socket node never was. Verified by screendumping both heads over QMP: with the console at 1280x800 the two are byte-identical, and after `schmode 1024 768` the virtio head carries the console at the new mode. Three consecutive boots of one image all reach a working control socket, where the previous commit managed one. Both supported configurations: one boot each, no traps, no panics, socktest and memfdtest green. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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| .. | ||
| architecture | ||
| branding | ||
| guides | ||
| history | ||
| plan | ||
| Website | ||
| licensing.md | ||
| README.md | ||
SchOS documentation
Four kinds of document, kept in four directories, because they answer four different questions and go stale at four different rates.
| architecture/ | What SchOS is | Present tense. Describes what is built and working. |
| plan/ | What SchOS will be | Future tense. Everything here is unbuilt. |
| guides/ | How to work on it | Imperative. Build it, test it, add to it. |
| history/ | Why it is the way it is | Past tense. Bugs whose cause is not visible from the fix. |
Plus two that belong to no category and apply to everything: licensing.md — read it before copying anyone else's code in — and branding/, which holds the marks and the rules for using them.
The rule that keeps this from rotting
When something is finished, it moves from
plan/toarchitecture/and is rewritten as a description of the thing rather than a record of building it.
A completed item is not a ticked checkbox. A ticked checkbox says the work happened; it does not say what the work produced, and six months later the checkbox is the only thing left and it explains nothing.
So finishing a piece of work has three steps, and the third is not optional:
- The code works and is tested.
- The plan entry is deleted.
- A description exists in
architecture/written for somebody who was not there — what it does, what shape it has, what it costs, and what it still does not do.
This is not bookkeeping. The tree has already proved it necessary: the network stack was finished, verified end to end, and for a month afterwards the only description of it anywhere was a checkbox in a roadmap, four levels of indentation deep, written in the past tense of somebody arguing for the work rather than explaining the result.
The "what it does not do" section is the one that pays. Every description in
architecture/ ends with one. A document that only lists a subsystem's
strengths is marketing, and the reader who most needs the document is the one
about to trip over a limitation nobody wrote down.
Start here
New to the tree → architecture/README.md, the system layer by layer, then guides/layout.md for where the files are.
Trying to build it → guides/building.md.
Wondering what happens next → plan/1.0.md, which is the finish line and the register of everything half-built. Then plan/README.md for the order.
About to start something new → the register, first. Nothing new starts while it has rows in it, and a row leaves only by being finished or deleted.
Something is broken and it feels familiar → history/. There is a good chance it is in there.
architecture/ — what SchOS is
| README | The system, layer by layer. Read first. |
| boot.md | Firmware to the first userspace process. |
| kernel.md | SchIFT: memory, processes, scheduling, traps, signals, SMP. |
| syscalls.md | The call table, and the Linux personality that lets real software run. |
| filesystem.md | The VFS, the buffer cache, procfs, mounts. |
| schfs.md | SchFS: the copy-on-write root filesystem. |
| devices.md | The device model, driver binding, the class vtables. |
| usb.md | xHCI, the USB core, and the class drivers. |
| graphics.md | Framebuffer, text rendering, console, and the crash screen. |
| terminals.md | The six virtual terminals, and how one is switched to. |
| networking.md | Drivers, lwIP, sockets — Unix and INET. |
| init.md | schinit, PID 1 as a role, and the job manifests. |
plan/ — what SchOS will be
| README | The three current decisions and the order they happen in. |
| 1.0.md | The finish line, and the freeze. What 1.0 contains, what is deferred, and the register of every half-built thing in the tree. |
| foundations.md | The kernel work everything else is blocked on. |
| wayland.md | The GUI stack, and what gets deleted to make room. |
| hybrid.md | Moving drivers out of the kernel. |
| schapi.md | The long-term API layering, and the compatibility promise. |
| roadmap.md | Everything else still open. |
guides/ — how to work on it
| building.md | Prerequisites and the build, per host. |
| testing.md | The harnesses, and what each one actually proves. |
| layout.md | Repository map, and how to add a program or a port. |
| adding-a-driver.md | Writing one, binding it, publishing its class vtable. |
branding/ — the marks
| README | Shift, the one mark: what it is for, the colour rule, why an icon and a mascot were removed, and why a raster is committed next to its SVG. |
history/ — why it is the way it is
| README | What belongs in here and what does not. |
| kernel.md | Bugs whose cause was nowhere near their symptom. |
| schfs.md | The filesystem's own, from the same period as its design. |
| moving-to-linux.md | The Windows-to-Fedora move, kept for the parts that recur. |
Writing one of these
Four conventions, all of them observable in the existing files:
State the cost. Every design choice gave something up. A document that does not say what is a document that will be argued with later by somebody who only sees the downside.
Prefer the measured number to the remembered one. "500 of 3565 files carry the advertising clause" is worth more than "some do", and it was worth the minute it took to count.
Write down the bug that shaped it. Half the non-obvious code in this tree is non-obvious because something failed once. If a design is strange, the strangeness is load-bearing and the reader deserves to know why before changing it.
No dates in headings. A date in a heading turns a description into a
changelog, and the description is the thing with a long life. Dates belong in
history/, where they mean something.