The tree had zero memory barriers — correct-by-accident on x86 (TSO + strong-
uncacheable MMIO), but a landmine for the first DMA driver and for ARM, which is the
win condition. Add /lib/mmio: typed volatile register access (read/write) plus mb /
rmb / wmb, lowered per-architecture (mfence/lfence/sfence on x86_64, dsb sy/ld/st on
aarch64) so the ordering rules are a named primitive, not scattered `asm volatile`.
`volatile` is not a barrier — it says nothing about ordinary stores (a DMA descriptor
in WB RAM) relative to a volatile doorbell write; wmb() between them is the fix.
Prove it on the one existing caller: hpet now does its register access through
mmio.read/write. It needs no barriers itself (pure MMIO, no DMA, UC grant on x86) —
the point is the typed, arch-portable access every driver should use; the barriers are
there for the DMA drivers to come.
New `mmio` module injected into addUserBinary; host test asserts the barriers assemble
and a register round-trips. Suite 37/37 plus host tests.
ipc_call and ipc_reply_wait grow a `send_cap` argument (r9) and a `received_cap`
return (r8): an endpoint travels alongside a message, installed into the receiver's
handle table. The transfer is a share, not a move — the endpoint's refcount is bumped
and the sender keeps its handle. If the receiver's table is full the call fails
-ENOSPC and the message is NOT delivered (a half-delivered capability is worse than a
failed send); a bad handle fails -EBADF. Both directions carry a cap: a client's call
hands one to the server (seen in the server's replyWait), and the server's reply hands
one back (seen in the client's call return).
This is the "open" primitive the driver model was blocked on: a bus driver mints a
per-device endpoint and hands it to a class driver, giving it a private channel to one
device without the 8-slot global name registry.
Kernel: shareCapability in ipc-synchronous.zig at both copy points; new
setSystemCallResult3 (r8, saved/restored by the syscall stub); Task gains
ipc_send_cap / ipc_received_cap. Runtime: callCap + Reply, replyWait gains send_cap
and Received.cap; plain call/replyWait delegate with no_cap. New abi.no_cap.
New ipc-cap test (two kernel tasks exercise both directions, each verifying the
endpoint it received is the same object shared, refcount bumped to 2). No class driver
consumes callCap yet — it lands with the first one. Suite 37/37 plus host tests.
The reorg moved user binaries under /system (init -> /system/services/init,
drivers -> /system/drivers/<name>, vfs-test -> /system/services/vfs/vfs-test), but
many comments and log strings still named the old /sbin/ home. Retarget them all:
kernel/loader/test comments and the two boot log lines, plus vision.md and the
driver-model.md proposed tree (also dropped the stale `d` suffixes and rt->runtime
there). The initial-ramdisk spawn log no longer fakes a /sbin/ prefix, since those
binaries live in different homes (services vs drivers).
Left the FSH design doc's /sbin and /lib rows alone — whether /sbin stays a
directory at all is a design call for its owner, not a stale-comment fix.
Follow-up to the monorepo re-org. Suite 35/35 plus host tests green.
POSIX compatibility is now its own library, library/posix/ (unistd, stdio),
layered strictly over the runtime — it calls the runtime's IPC/heap, never
system calls directly. The runtime is now POSIX-free (the danos-native
application ABI). The VFS wire protocol is danos-native throughout
(Stat -> FileStatus, .stat -> .status, O_CREAT -> create); the POSIX layer
maps the POSIX spellings at the boundary. The coding standard's ABI-name
exception is scoped to one place: a file is allowed POSIX spellings only if it
lives under library/posix/ — everywhere else, danos naming with no exception.
Naming fixes, all mechanical:
- initrd -> initial-ramdisk: the source file, the module, the tool
(make-initial-ramdisk.py), the artifact (initial-ramdisk.img, including the
bootloader's load path), and the identifiers.
- system/kernel/device-service.zig -> devices-broker.zig: it is ring-0 kernel
code (the trusted device table + claim capability), not a ring-3 service. The
future user-space device *manager* (policy) will live in system/services/.
- Dropped the daemon `d` suffix: hpetd -> hpet, busd -> bus. A driver lives in
system/drivers/, so the folder already says what it is; encoding the role in
the name too is redundant. The coding standard drops that exception.
- system/devices/aml/interp.zig -> interpreter.zig (the type was already
Interpreter).
The source layout now mirrors the runtime filesystem hierarchy
(docs/danos-file-system-hierarchy-FSH.md): what lives under system/ in the
source is what a running danos represents under /system. Each service and
driver is a sub-project directory that is its own Zig module — cross-project
references go by module name, never by a path into another project's files.
Moves (all git mv, history preserved):
- src/ -> system/ (danos internals; the self-representation)
root.zig -> danos.zig (the kernel<->user contract module)
kernel/arch/ -> kernel/architecture/ (arch -> architecture)
device/ -> devices/ (what /system/devices reflects)
boot/ -> /boot (the loaders, top level)
- sbin/ -> split by role:
init, vfs -> system/services/<name>/<name>.zig
hpetd, busd -> system/drivers/<name>/<name>.zig
vfs-test -> system/services/vfs/vfs-test.zig (inside the vfs project)
- lib/ -> library/runtime/ (room for other libraries beside runtime)
The VFS wire protocol becomes its own module, system/services/vfs/protocol.zig
("vfs-protocol"): the vfs sub-project exposes its interface, and the runtime's
file layer imports it by name. First instance of the "protocol module" pattern
(docs/driver-model.md); usb/block will expose theirs the same way.
Also: fix a naming-standard violation in the protocol — Op -> Operation (and
req -> request, _pad -> _padding). Docs updated: /system/services added to the
FHS doc, a repository-layout section added to the docs index, and stale source
paths swept across comments and docs.
Runtime boot paths are unchanged (the bootloader still loads /sbin/init);
aligning the runtime filesystem to the FHS is a separate follow-up. Suite 35/35
plus host tests green.
Daniel Samson