df1394eaa3
SCFF, the SchOS Compressed File Format (include/fs/scff.h), is a block image cut into 128 KB chunks, each its own zstd frame, behind an index. tools/mkscff writes it from fs-ram.img on every core (-19, 11 s) and checks each chunk decompresses to itself. The kernel carries the .scff as its ramdisk and unpacks a chunk the first time a block in it is read; zero blocks share one page. The kernel and the ISO are the compressed size, and the root costs memory only for what is touched. See docs/architecture/scff.md. zstd 1.5.7 comes from ports/zstd like uACPI: the decoder is compiled into the kernel at -O2, with a static context and a 64 KB stack of its own, and mkscff builds the whole library from the same release. world now has xorg-server, the fbdev and evdev drivers, xinit, Window Maker, xterm and DejaVu, and /root/.xinitrc runs wmaker. That root is 358 MB, 102 MB as SCFF. The ISO no longer carries the root a third time as an ISO 9660 tree, which nothing read. schos.iso: 1389 MB -> 318 MB. El Torito keeps its own copy of the EFI image, the layout real machines have booted. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
80 lines
3.8 KiB
Markdown
80 lines
3.8 KiB
Markdown
# apk: Alpine's packages on SchOS
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Alpine is musl with a different init, and SchOS is musl with a different
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kernel. Alpine's binaries run on SchOS unmodified: its dynamic linker, its
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busybox, and apk itself, fetching over TLS through SchOS's network stack.
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So instead of porting programs one at a time, SchOS can install them.
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## The model
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The root filesystem is an apk-managed root:
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| Part | Where it comes from |
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|---|---|
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| musl, busybox, apk-tools, alpine-keys, CA certificates | Alpine's minirootfs (`ports/alpine`) |
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| what `ports/alpine/world` lists (zsh, terminfo, ...) | Alpine's packages, pinned in `world.lock` |
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| schinit, its jobs, SchOS's tools, toybox, mksh, configuration | **schos-base**, an apk package the build makes from `sysroot/` |
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`apk add` installs anything from Alpine's main and community repositories.
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`apk upgrade` updates Alpine's packages, and schos-base from the SchOS
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repository at `/var/lib/schos/repo`.
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PID 1 is still schinit. Alpine's OpenRC is not installed, and packages that
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ship OpenRC services install them where nothing reads them.
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## Who owns what
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Where Alpine and SchOS both have a program, Alpine's wins, and SchOS keeps
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only what is its own (see `tools/posix/mkaroot.sh`):
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- `/bin/sh`, `cat`, `sed`, `find` and the rest are busybox. Alpine's package
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scripts are written against busybox.
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- zsh is Alpine's. SchOS keeps its `zshrc` and `zshenv` (`replaces=zsh`).
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- `/etc/os-release` and `/etc/motd` are SchOS's (`replaces=`).
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- `passwd`, `group` and `profile` are Alpine's. schos-base's post-install
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sets root's shell to zsh, and SchOS's profile is `/etc/profile.d/schos.sh`.
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- mksh is `/bin/mksh`. schinit's recovery shell looks for it first because it
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is static: a broken musl cannot take recovery down with it.
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## Building
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make qemu boots build/schfs.img, the root as a 1 GB SchFS disk
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make iso the same root as the live system's ramdisk
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make alpine-lock re-resolve world against Alpine (needs the network)
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It is the only root. sysroot/ is what schos-base is packaged from.
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Only `alpine-lock` asks Alpine what is current. A normal build installs
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exactly what `world.lock` names: files in `dist/alpine/`, fetched once and
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checked against the lock's sha256, and against Alpine's signatures by apk.
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schos-base and its repository index are signed with a key made on the first
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build (`build/apk-keys/`, never committed). The root trusts it beside
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Alpine's keys.
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## Kernel work this needed
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All of it found by running apk:
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- **TCP receive window:** it reopened before the reader drained, so lwIP
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refused data and the sender waited on retransmission timers (5 KB/s). It
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now reopens on read, with a 32-segment window.
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- **mmap address reuse:** freed ranges were never reused, so musl's malloc
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used up the 256 mapping records with 780 MB of RAM free.
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- **unlinkat / renameat:** bare `-1`, read as EPERM, where apk expects ENOENT;
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renameat could not replace its target, and wrote v1 dirents into SchFS.
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- **`#!` scripts in execve**, and ENOEXEC: apk runs triggers directly.
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- **chroot**, and mounting devtmpfs and proc more than once.
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## Next
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- The live ISO runs the apk root from RAM. The image in the kernel is only
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what the root holds; at boot the volume grows into half of the free memory
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(4 GB of root on an 8 GB machine), backed by pages as they are written.
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Xorg installs into it in about a minute. All of it is gone at reboot. Keeping packages needs an installer that writes the root
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to a SATA or NVMe disk, and a kernel that finds its root there by the
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SchFS GPT type rather than as IDE disk 1.
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- Xorg and Window Maker are in `world`, so the image starts with them:
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`startx` runs `wmaker` from `/root/.xinitrc`. Mesa brings LLVM with it,
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about 200 MB of the 358 MB root; the root ships compressed
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([SCFF](../architecture/scff.md)), so that costs about 60 MB of ISO.
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