| Filename | Latest commit message | Latest commit date |
|---|---|---|
182cc76588
Two things, both asked for. **The crash report no longer says which monitors it reached.** "The report is on the virtio-gpu display too" was a line about the crash screen printed on the crash screen. The report says what happened and where to read it again; that is not part of it. **And the second head now shows the F8 menu and the boot.** It used to be black until vgpud started several seconds into userspace -- through the splash, through the menu, through every boot message -- which from the outside is indistinguishable from a display that does not work. Three stages now cover the whole boot and hand over to each other without coordinating: *The loader.* LocateProtocol() answers with the first GOP and offers no way to ask for the rest, so the rest are found by handle and fed the primary's framebuffer as a Blt source at the points where a screen is finished: the menu, the resolution chooser, system information, the splash, each segment of the kernel load. Blt rather than a second framebuffer to draw into, because a virtio GOP does not have one -- the same fact that made a virtio-only machine reboot-loop two commits ago. *The kernel.* gfx remembers which rows were drawn, as one span rather than a list of rectangles, because console output is lines and a span is what lines make. display_mirror_console() copies that span across: a line of boot text is one cell-row transfer, not a screen. Primed once after pci_init(), because a display that has just appeared has a black scanout and the console it should be showing was drawn by the loader into a framebuffer it knows nothing about. *Then vgpud*, from the same console framebuffer, unchanged. **Two bugs found building it, both worth the retelling.** The mirror ran per character from inside vt_feed -- which is inside the console lock -- and vga_disp_acquire() announces its back buffer with a cprintf. A CPU taking a lock it already holds, with a call chain that said exactly that. It runs at the end of consolewrite() and cprintf() now, outside the lock, which is also the better batching: one transfer per write instead of one per character. And "is this the console's own screen" was asked of the pointer acquire() returned. vga_fb hands back a back buffer it copies onto the console's framebuffer afterwards, so on a one-screen machine the answer was "a different screen" -- and the console was mirrored onto itself through two megabytes of intermediate, allocated for the purpose. display_ops grew scanout_phys, which is a fact about the hardware rather than a policy a driver can get subtly wrong, and it is asked first: it has no side effects and acquire() has two. Verified with two heads under QEMU, screendumping the virtio head every 400 ms from power-on: splash, splash, splash, then the console, and it stays. The F8 menu appears on it; choosing 1024x768 there brings both heads up at 1024x768 byte-identical. A panic still reaches both. Both supported configurations: one boot each, no traps, no panics, socktest and memfdtest green. One gap remains and is documented rather than hidden: while the kernel's driver resets the device during probe, QEMU shows "Display output is not active" for a fraction of a second. A device being taken over has no scanout until the new driver sets one. 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.