| Filename | Latest commit message | Latest commit date |
|---|---|---|
9e6d8dd4e3
sendmsg/recvmsg with SCM_RIGHTS. Item 1 of docs/plan/foundations.md and
mechanism 1 of docs/plan/hybrid.md, which are the same primitive seen from two
directions: Wayland's wl_shm_create_pool passes a file descriptor with no
integer-shaped alternative, and handing a driver process the device it is
allowed to touch is the same act. Both plans stopped here.
Linux's structures byte for byte -- msghdr, cmsghdr, the CMSG_ macros -- because
the programs that need this are not ours. libwayland and toybox both call
recvmsg with Linux's headers and would not notice a friendlier door.
The delivery rule is the whole design. A batch of descriptors is pinned to the
stream position of the first byte of the message that carried it, and that has
two halves: a reader arriving at that position is handed them, and a reader that
has not reached it is stopped SHORT of it. Leave out the second half and a
program asking for 4096 bytes swallows three messages and is handed one
message's descriptors, with nothing in the result saying which. socktest checks
exactly that: two one-byte messages, an eight-byte read, one byte back.
The kernel holds a reference to every descriptor in flight, so a sender may
close its own copy the moment sendmsg returns. Giving that reference back is the
part that leaks if it is not written down, and there are three ways a message
ends:
- received with room installed in the receiver's table
- received without room, or by
plain read(2) closed; MSG_CTRUNC for the first case
- never received, socket closed closed by sockclose
The middle row looks like a choice and is not: holding kernel references for a
receiver that has proved it is not looking is a leak with extra steps.
No garbage collector. A socket descriptor sent over that same socket and never
received holds a reference to the socket that holds the reference to it, and
neither close reaches zero. Linux carries several hundred lines for this.
Nothing on either plan passes a socket over a socket -- Wayland passes memory,
the driver work passes devices -- so it is a bounded leak that is documented
rather than a silent one.
Fourteen checks in cmd/socktest, and every one moves data through the descriptor
rather than inspecting it. The descriptor passed is always a pipe end, because a
pipe announces its own lifetime: a read of a pipe whose writers are all gone
returns 0, which turns "was the kernel's reference released" -- otherwise
invisible from userspace -- into a value a test can compare.
Two bugs fell out, neither in the new code:
- sockpair() never set the socket's domain, so every socketpair() socket
claimed domain 0. Invisible while the data paths asked only whether a socket
was AF_INET or AF_NETLINK, since zero answers "neither" correctly.
SCM_RIGHTS asks "is this AF_UNIX", and zero is wrong for that one.
- pipe_poll() reports POLLHUP but not POLLIN at end of file, so a non-blocking
read of a pipe whose writers had all gone returned EAGAIN forever instead of
0 -- a program that polls and reads spins waiting for an end that already
happened. sockreadable() always had the equivalent condition; the pipe path
did not. Found because the test helper for "is this descriptor closed" is a
non-blocking read of a pipe.
projects/schcom/README.md said SCM_RIGHTS was done for a long time while nothing
in the kernel implemented it, and an entire GUI plan was drawn on that line.
It is true now, which is not the same as it having been right, and the README
says so.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
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| schcom | ||
| schde | ||
| schfs-linux | ||
| schinst | ||
| schwm | ||
| README.md | ||
projects/
Things that run on SchOS rather than things that are SchOS.
Everything above this directory — kernel/, boot/, lib/, cmd/,
include/ — is the operating system: it boots, it owns the hardware, and it
is one program that either works or does not. Everything in here is an
ordinary program that talks to it through syscalls, exactly as toybox does.
The split exists because the alternative gets bad quickly. A compositor, a window manager and a desktop are each larger than the kernel will be for a long time. Grown inside the OS tree they would blur into it: a compositor would start reaching into kernel headers because they are right there, the build would grow a dependency from the kernel to a GUI, and "does SchOS boot" would stop having a clear answer. Keeping them separate forces the boundary to be a real interface — syscalls and protocols — rather than a shared header nobody meant to share.
Concretely, code in here:
- links against the sysroot's libc, never against kernel headers
- talks to the kernel only through syscalls and
/dev - can be built, run and debugged without rebuilding the kernel
- may be split into its own repository later without untangling anything
What lives here
| Directory | What it is |
|---|---|
schcom/ |
SchOS Compositor. Owns the display, composites clients, routes input. |
schwm/ |
SchOS Window Manager. Window placement, decoration, focus, on top of Schcom. |
schde/ |
SchOS Desktop Environment. Panel, launcher, settings, file manager. |
schinst/ |
The installer, the installation environment, and .sip tooling. |
schfs-linux/ |
SchFS as a filesystem for Linux. FUSE first, a kernel module later. |
schfs-linux/ is written to stand on its own. It does not mention SchOS
anywhere, and that is deliberate rather than an oversight: it is intended to be
the first piece released, and it has to make sense to somebody who has never
heard of the OS it came from — a filesystem is judged as a filesystem. The
connection can be made later, once there is a finished system to connect it to.
Practically, that means anything added there needs its own licence header, its
own README framing, and no cross-references into this tree. It shares the
format with kernel/fs/schfs/, not the prose.
They stack: SchDE needs SchWM needs Schcom needs the kernel. Nothing points the other way, and nothing here is a dependency of the kernel build.
Status
All four are scoped and none is started. What each is waiting on is written
in its own README, and the ordering is in docs/plan/roadmap.md.
The short version: Schcom cannot start until the kernel has unix domain
sockets (for the client protocol and for passing buffer handles) and raw
input events (a /dev/input that bypasses the tty line discipline).
Shared memory and framebuffer mmap are already done.