Three services had each written the same thing and got it three different
ways: input polled the process list to notice a dead subscriber, and only
when someone else subscribed; the power service never noticed at all; the
device manager noticed drivers but not subscribers. The harness owns the
table now, driven by the events a protocol declares — it registers on the
reserved verb, frames each event once, posts to everyone interested without
waiting on any of them, and reclaims a slot when the kernel says its owner
died. Interest masks moved to the envelope, so a subscriber that wants only
mice asks the same way everywhere.
Two consequences the plan had not foreseen. The device manager now hears a
supervised child's death twice, once as its supervisor and once as a
subscriber, so restart backoff counted every crash twice and gave up after
half as many; it retires the id before counting. And the kernel's published
exit table had eight slots for what is now six subscriptions in a plain
boot, so it holds sixteen.
The other half is a hole the design named early and left standing: a
backend handed out a small integer and then honoured it from anyone. A
process that guessed a file's node id read another client's file; a display
layer had no owner at all, so any client could reconfigure or destroy any
layer; a USB device token was never checked against the client that opened
it. Each is now bound to the task that opened it, and a wrong owner gets
exactly what an unknown id gets — the refusal must not become the oracle
the identical answers elsewhere were designed to remove. Closing a file
changed with it: it used to succeed unconditionally, which would have told
a caller which ids existed.
Suite 111/111, with a new case in which one process holds a file and a
layer, hands both ids to a second process, and finds them untouched after
that process has tried everything with them.
The folded header stops being a rule in a document and becomes the layout
on the wire. Verbs number from sixteen, leaving describe, enumerate,
subscribe and unsubscribe reserved and answered the same way by every
provider — none of them writes a line to do it. What each protocol used to
carry in a field of its own now travels in the header: a vfs node and a
display layer are the packet's target, and a reply opens with a status the
envelope stamps rather than one each protocol spelled for itself.
Display gains the most. One forty-byte request had served eleven verbs, so
attach_scanout smuggled stride through x, refresh through y and format
through colour, and every coordinate crossed as a bitcast. Per-operation
structs end all three: the fields have their own names and their own signs,
and the tile payload grows to 224 bytes because the prefix shrank. Scanout
loses a message maximum of 64 it had no business declaring — it answers
calls, and the floor for a call is 256 — and virtio-gpu stops hard-coding
that number at its harness.
Two changes are semantic rather than notational. A directory now ends at an
entry with no name, because the fixed part of a reply always travels and a
zero-length reply no longer exists to mean anything. And input joins the
service harness, the last loop in the tree that answered no ping and heard
no terminate; its subscriber table, its pruning and its fan-out are the
same code, and a shutdown now asks it to stop instead of killing it.
A new conformance case reads the registry's own listing and asks every
protocol it finds for its name, its version and its verb count, then offers
a verb nobody defines and requires -ENOSYS — the envelope's promise,
checked against providers rather than against itself. What it cannot reach
in that boot it names on the serial line instead of passing quietly.
Suite 110/110.
A protocol is reached by name now, not by a compile-time integer. Init is
PID 1 and already knows which binary it started, so init serves /protocol
as a vfs backend: bind claims a contract with the provider's endpoint
attached, open answers with that endpoint as the reply's capability, and
readdir lists what is bound with the task and binary behind it. The kernel
reserves the prefix — nothing may mount over it, under it, or unmount it —
and ServiceId, ipc_register and ipc_lookup are gone, their syscall numbers
left vacant.
A bind is authorized by who the caller *is*: the kernel-stamped binary
together with the supervising task's identity, matched against
/system/configuration/protocol.csv. Identity, not spelling — spawn is
ungated, so an attacker can run any bundled binary, and a name-only rule
would have let it launder grants through an init of its own making. A name
a live process holds is refused to everyone else; a dead one's is released.
Three review rounds against a hostile ring-3 process found what 108 green
tests could not, because the suite contains no attacker. Publishing init's
supervision endpoint as the registry put PID 1's mailbox in every process's
hands, where two forged bytes reached the shutdown path: privileged traffic
is now believed only from the task that holds the contract it speaks for.
A capability arriving on a request outlived every path that ignored it,
one handle per call until the table was full — in init, and in the harness
ten services share — so the arriving capability is owned by the turn and
released unless a handler says otherwise. And the kernel let anyone holding
an endpoint handle aim signals, timers, exit notices and interrupts at it:
binding now requires having created it.
Suite 108/108. The new protocol-registry case asserts eleven properties,
each one an attack that must fail.
/etc/init.csv and /etc/devices.csv become /system/configuration/*.csv (the
repo's etc/ moves to system/configuration/, mirroring the runtime tree),
/var/log becomes /system/logs, and /mnt/usb becomes /volumes/usb. The
kernel VFS gains a carve-out so FAT may serve exactly /system/configuration
and /system/logs beneath the initrd-backed /system while /system and /test
themselves stay unshadowable; FAT's single /var mount splits into those two
rewritten mounts. The kvfs readdir check learns /system's third child and
the ramdisk spawn sweep skips the configuration tree.
Suite 106/106.
Replaces L2's interim DMA pool (every buffer reachable by every claimed
device) with true per-grant confinement: a device reaches only buffers
whose capability was delegated to its driver.
Kernel:
- DmaRegionObject (handle kind 2): a delegation token naming a dma_alloc'd
region, passable across processes on the IPC cap slot like an endpoint
or shared-memory object. Frames stay owned by the allocating address
space (freed on dma_free/teardown as before); the token carries a `dead`
flag so a stale downstream handle can no longer bind a freed region.
- dma_alloc gains the dma_shareable flag: it returns a capability handle
in r8 and every region is tracked in a registry. A task's own regions
auto-bind into the devices it claims (its rings just work); foreign
buffers are bound explicitly.
- dma_bind / dma_unbind / handle_close syscalls (51-53). dma_bind maps a
held region (or shared-memory) capability into a claimed device's domain;
it is idempotent. handle_close reclaims a table slot (raised 16 -> 32).
- dma_free and task death unmap a region from every domain and invalidate
BEFORE its frames return to the allocator — the stale-IOTLB use-after-
free window, closed structurally.
Protocols (flag-day): block gains attach, usb-transfer gains dma_attach —
each carries a region capability on the cap slot. fat allocates its bounce
buffer shareable and attaches it; usb-storage allocates its transport
buffers shareable, attaches them to the controller, and forwards fat's
capability downstream; usb-xhci-bus binds and closes; virtio-gpu binds its
shared scanout surface. The physical addresses on the wire are unchanged
(identity IOVA), so no register-programming code moved.
Cross-process DMA (fat -> usb-storage -> xHC) now flows only through
delegated capabilities. iommu-usb-storage / iommu-usb-hid / iommu-fault
all green under per-grant enforcement; 104/104 overall (fail-open paths
unchanged).
Every user binary and the two device-logic library modules (pci, usb) now
`@import` the concern modules directly instead of aliasing through `runtime`:
runtime.ipc/process/time/service/input/block/display -> @import("<module>")
runtime.device / runtime.device_manager -> @import("driver")
runtime.fs -> @import("file-system")
runtime.Thread -> @import("thread").Thread
runtime.system.{write,writeRecord,klog*} -> logging.*
runtime.system.{sleep,timerOnce,wallClock,clock} -> time.*
runtime.system.{spawn*,kill,exit,yield,processes,...}-> process.*
runtime.system.{mmap,munmap,PROT_*} -> memory.*
runtime.dma.* / runtime.shared_memory.* / runtime.allocator -> memory.*
Each consumer keeps its own alias name (e.g. `const device = @import("driver")`),
so call sites are unchanged and there are no collisions with local `driver`
variables. build.zig now injects the concern modules into every user binary via
`default_imports`; pci/usb module import lists were updated to match.
The `runtime` and `system` shims remain for one more step (root.zig still uses
runtime); they are deleted in C5. Nothing but root.zig imports `runtime` now.
Verified: zig build, zig build test, and 17 QEMU cases (smoke, device-manager,
logger, fat-mount, fat-mutations, usb-storage, usb-hid, display-native,
virtio-gpu, input, thread-spawn, thread-mutex, process-kill, shared-memory,
driver-restart, acpi-ps2, pci-scan).
vfs-protocol -> library/protocol/vfs/vfs-protocol.zig. fat, its only consumer,
now imports the module directly (const vfs_protocol = @import("vfs-protocol"))
instead of through runtime.vfs_protocol, and the runtime re-export is deleted.
The runtime's own client (runtime.fs) still imports the module by name.
zig build + test green; vfs, fat-mount pass.
The FAT engine read and wrote one sector per device command — one SCSI
READ(10)/WRITE(10) over USB Bulk-Only Transport per 512 bytes, so every
file read, log write, and cluster fill paid a full USB round trip per
sector. The lower stack (runtime.block, the block protocol, usb-storage's
read10/write10 + count*block_size data stage) already carried a
multi-sector count; only the engine's BlockDevice interface and IpcBlock
were single-sector.
Widen BlockDevice to move a run of `count` contiguous sectors per call
(readBlock/writeBlock kept as count=1 wrappers, so metadata call sites —
FAT sectors, directory entries — are untouched). readFile and writeFile
now coalesce the aligned full-sector middle of a transfer into one command
(capped at the cluster boundary and the 4 KiB bounce = 8 sectors), reading
straight into / writing straight from the caller's buffer with no staging
copy. Full-sector writes skip the read-modify-write entirely, since they
overwrite the whole sector. Partial head/tail sectors keep the per-sector
RMW path.
IpcBlock passes count through to the block driver and sizes its bounce from
engine.max_transfer_sectors (already 4 KiB — no new allocation). A new
spc=8 engine test proves runs coalesce (a 21-sector overwrite drops from
>=21 writes to <=5) and that reads/writes round-trip byte-identical,
including an unaligned offset spanning a cluster boundary.
Full QEMU suite 92/92.
B2 — the 1-in-3 boot-time READ CAPACITY failure, root-caused: the xHCI
library's awaitTransfer claimed ANY unclaimed transfer event as its own
completion. An interrupt-endpoint event whose TRB pointer no longer
matched the armed subscription (an error or stale completion from the
keyboard/mouse polling concurrently with storage bring-up) fell through
and was misread as the bulk transfer's completion — desynchronizing the
mass-storage bulk protocol in controller state that SURVIVED driver
restarts, so every retry failed too. Awaited transfers now match the
event's slot id and endpoint DCI; foreign events are dropped and named.
Twelve consecutive runs of the previously-flaky cases pass; the full
suite is green with none of its old intermittents.
B1 — and when storage does fail transiently, the system now heals
instead of giving up forever: a nonzero exit maps to ExitReason.aborted
(a deliberate FAILURE exit — supervisors restart those with backoff,
unlike a clean .exited), usb-storage exits nonzero when a PRESENT
device fails bring-up, and the fat service no longer blocks its harness
polling for a block device and then dies — it serves immediately
(requests fail politely), retries on a 500 ms timer, and mounts
whenever storage appears, including after a driver restart.
runtime.fs now routes every path through fs_resolve: kernel-served
/system nodes are read via fs_node (tokens, no open state); everything
under a userspace mount goes straight to the owning backend's endpoint
with the kernel-rewritten mount-relative path — one syscall of naming,
then the unchanged vfs-protocol rendezvous, public API untouched. mkdir/
unlink/rename resolve-then-forward (rename checks both paths land on
the SAME backend); mount is the fs_mount syscall.
The fat server mounts twice — /mnt/usb from the volume root and /var
from its /var subtree — so the logger now writes the FHS path
/var/log/<boot-stamp>/... and swapping the persistent medium later
touches only fat's two mount calls. With clients holding fat's node ids
directly, fat records each handle's owner, checks it, and sweeps a dead
client's handles via the published exit events (the old router's
pattern, now where the state actually lives).
The userspace vfs server and its router die; ServiceId.vfs=1 stays
reserved-retired; protocol.zig moves to system/vfs-protocol.zig (the
wire contract is backend-only now). vfs-test becomes the ring-3 proof
of the kernel VFS (own-binary ELF magic through /system, read-only
refusals, listing); vfs-client-death becomes the fat sweep test over
the full storage chain, with a ring-scanning check (the last-write
buffer is too racy under a chattering tree).
createFile/createDirectory now build long-name chains: a mangled STEM~N
8.3 alias (collision-checked per directory), the standard rotate-add
checksum, and 13-UCS-2-per-entry pieces written last-logical-first into
a contiguous free-slot run (found sector-wise, growing the directory as
today). Write order is chain first, 8.3 entry last, so an interrupted
create leaves only skippable orphans. Uppercase-compliant 8.3 names
keep the bare-entry fast path; lowercase names now get a chain so their
exact case survives — matching tools/make-fat-image.py. rename stays
8.3-only (documented; nothing needs more yet).
allocateCluster drops its from-cluster-2 rescan (measured ~1 s/cluster
on a part-full volume, a 37 s shutdown flush in the lost M19 build):
a next-free hint (rewound by frees) plus a FAT-sector LBA cache turn
the scan into one device read per FAT sector.
mkdir now refuses an existing name (no duplicate entries), and
runtime.fs gains makePath (mkdir -p) for the logger's nested per-boot
directories. Engine tests cover the log-directory shape, ~N collisions,
chain unlink/reuse, the 8.3 fast path, and the checksum.
library/runtime/log.zig wires std.log to the tagged ring: the root shim
installs std_options for every binary (programs may override), logFn
formats one line per record and emits it with its level via
debug_write — the payload no longer carries the process's name; the
kernel stamps identity structurally and the serial renderer prints the
'<binary path>: ' prefix, so the transcript keeps its shape.
Migrate every writeLine/logLine/log helper family (init, vfs, fat,
device-manager, acpi, pci-bus, ps2-bus x3, usb-hid x2, usb-storage,
usb-xhci-bus, virtio-gpu — 104 call sites) to std.log.info, dropping
the hand-written prefixes. A leveled record is a complete line by
contract (raw emissions may still build lines from pieces). Test
fixtures and the display/input services keep raw writes for now — their
ring records are attributed by the kernel regardless.
Harness regexes follow the renamed prefixes (usb-hid-keyboard,
discovery) and path-named restart lines.
init writes /mnt/usb/DANOS.LOG at shutdown and then enters S5 — but the write sat in the USB flash controller's write cache and was lost when power was cut, because nothing issued SCSI SYNCHRONIZE CACHE. Invisible in QEMU (its backing file commits immediately); real on hardware. The boot-time flush survived only because the machine kept running afterward and the cache drained on its own.
- block protocol gains a flush op; usb-storage serves it with SYNCHRONIZE CACHE (10); runtime.block gains Device.flush()
- the FAT server tracks whether blocks were written and, on a file close, commits the device cache (durable-on-close — the right default for removable media, and it makes init's existing shutdown close() persist the log before S5, no init/VFS change needed)
- verified the SYNCHRONIZE CACHE actually reaches the driver on each dirty close; usb-storage/fat-mount/mutations/rename/mtime/log-flush all green
Completes Phase 2: the FAT filesystem now stamps and reports a real modification
time, built on the Phase 2d(i) kernel wall-clock. This is the last stat field the
compiler's build cache needs to reason about (source vs cached output).
- on-disk.zig: fatToEpoch / epochToFatDateTime convert between the two 16-bit DOS
date/time fields and Unix epoch seconds (UTC — FAT has no timezone). Host-tested
round-trip + an absolute check (1577836800 == 2020-01-01).
- engine: a settable current_time_epoch that create/write stamp into the entry's
write (and creation) date/time; Node/Listing gained an mtime decoded from those
fields on read. Host test: a create stamps the mtime, read back through resolve
and listEntry.
- vfs protocol FileStatus + runtime.fs.Attributes gained an mtime field; the fat
server sets current_time_epoch from runtime.system.wallClock() per request and
returns mtime from stat. The flat ramfs reports 0 (it has no timestamps).
- fat-test reads the created file's mtime through stat and checks it is a real
current time, behind a new `fat-mtime` QEMU case.
Verified against the host: the guest stamped mtime 1783971676 while the host clock
was 1783971680 (boot+test lag) — the file's mtime is real current time. zig build,
zig build test (the epoch<->DOS conversions + the engine mtime test),
zig build check-fat-image, and a sequential QEMU sweep — fat-mount, fat-mutations,
fat-rename, fat-mtime, vfs, vfs-client-death, log-flush, orderly-shutdown,
initial-ramdisk, smoke, wall-clock, usb-storage — all green. mode/inode remain.
Completes the Phase 2 FAT mutation set (truncate, mkdir, unlink, rename).
- engine: rename(dir, old_name, new_name) rewrites an existing entry's 8.3 name in
place within the same directory. Refuses a missing source, a non-8.3 target, or a
name that already exists; drops any long-name entries on the old file (it takes
its new 8.3 name), LFN-aware like removeFile. Cross-directory and long-name-
preserving rename are noted limitations. Host-tested (rename keeps contents;
collision, non-8.3, and missing-source are refused).
- vfs protocol: a `rename` operation whose payload is old-path, a 0x00 separator,
then new-path.
- VFS router: a forwardRename helper + a `.rename` case that requires both paths
under the same mount (cross-filesystem rename is refused) and forwards the
mount-relative old+new.
- fat server: a `.rename` handler that requires the same parent directory and calls
engine.rename.
- runtime.fs: rename(old_path, new_path).
- fat-test now renames the file it created (before removing it) and asserts the old
name is gone, behind a new `fat-rename` QEMU case.
Verified: zig build, zig build test (the engine rename unit test), zig build
check-fat-image, and a sequential QEMU sweep — fat-mount, fat-mutations, fat-rename,
vfs, vfs-client-death, log-flush, orderly-shutdown, initial-ramdisk, smoke — green.
The engine gained mkdir/unlink in Phase 2a; this exposes them as first-class
filesystem operations so programs can use them.
- vfs protocol: two new path-based operations, mkdir and unlink (appended, so
existing opcodes/offsets are unchanged).
- VFS router: a forwardPath helper relays a path-based op under a mount to its
backend; the mkdir/unlink cases forward to the mounted filesystem (the flat
ramfs refuses them — it has no directories).
- fat server: mkdir -> engine.createDirectory, unlink -> engine.removeFile, each
resolving the parent via a shared splitParent helper (also used by open-create).
- runtime.fs: makeDirectory(path) and remove(path).
- fat-test now exercises the whole path — mkdir /mnt/usb/TESTDIR, create + write +
read a file inside it, then remove it — behind a new `fat-mutations` QEMU case.
Verified: zig build, zig build test, zig build check-fat-image, and a sequential
QEMU sweep — fat-mount, fat-mutations (mkdir/write/read/unlink through the mount),
vfs, vfs-client-death, log-flush, orderly-shutdown, initial-ramdisk, smoke — green.
The FAT engine could create, read, write, and grow files, but never free clusters
or make directories — so overwriting a shorter file left a stale tail (a real bug:
corrupt boot-log re-flushes, and later corrupt compiler cache/.o files). This adds
the mutation half of the engine, with the corruption fix wired all the way through.
Engine (system/services/fat/engine.zig), all host-tested:
- freeChain: return a cluster chain to the pool (bounded against a corrupt cycle) —
the shared primitive under truncate and remove.
- truncate: free the chain and zero the entry's size/first-cluster (O_TRUNC).
- createDirectory (mkdir): allocate + initialise a cluster with "." and ".." and add
the directory entry to the parent.
- removeFile (unlink): free the chain and mark the 8.3 entry plus any preceding
long-name entries deleted, so a reused slot can't inherit an orphaned long name.
Refuses directories.
- createFile now shares a common addEntry helper with createDirectory.
O_TRUNC wired end to end: a truncate open-flag (vfs protocol) that the router already
forwards; runtime.fs.OpenOptions.truncate; and fat's handleOpen calls engine.truncate
on an existing file. The boot-log flush (log-flush + init) now opens with truncate, so
a shorter log on a later boot of the same stick leaves no stale tail — closing the
caveat from the boot-log work.
mkdir/unlink are engine-complete and host-tested but not yet exposed as VFS
operations / runtime.fs methods (they are new path-based ops needing router cases);
rename and the richer stat (mtime/mode, blocked on wall-clock) remain. See
docs/zig-self-hosting.md (Phase 2).
Verified: zig build, zig build test (8 engine host tests, incl. truncate, the
overwrite-no-stale-tail regression, remove, and mkdir), zig build check-fat-image, and
a sequential QEMU sweep — fat-mount, log-flush (DANOS.LOG read back at 11804 bytes,
clean, with the truncate-based final flush), vfs, vfs-client-death, usb-storage,
orderly-shutdown, initial-ramdisk, smoke — all green.
The first step of the Zig self-hosting roadmap (docs/zig-self-hosting.md): give
danos programs a danos-native file API and remove the premature POSIX compatibility
shim. This also resolves the earlier misplacement of a full-write helper into the
compat layer — that behaviour now lives natively in runtime.fs.File.writeAll.
- library/runtime/fs.zig: the danos-native file client over the VFS (open/read/
write/writeAll/seekTo/attributes/close, directory listing, mount). Handles are
*values* — a File/Directory owns its VFS node id and byte offset — so there is no
per-process fd table or descriptor limit, unlike the POSIX fd model the shim
emulated. This is where the operations that later become std.os.danos are staged.
- Retire library/posix/ (unistd, stdio): only five call sites used it, all file
operations, all migrated to runtime.fs — fat (mount), the vfs-test and fat-test
clients, and init/log-flush (the boot-log flush). stdio was already dead.
- build.zig: drop the posix module, its addUserBinary parameter, the per-binary
import, and the ~26 call-site arguments.
- Docs: the VFS protocol's client is now runtime.fs; the docs index and
coding-standards note posix is retired and the foreign-ABI naming exception now
applies to the future std.os.danos seam; the process-lifecycle note points the
future musl layer at that same seam rather than the deleted directory.
Deferred by design (see the roadmap): the C-ABI runtime.os errno seam is built at
fork time (its shape must match std/os/danos.zig); truncate/mkdir/rename are
Phase 2; stdio-byte fds and cwd are later slices.
Verified: zig build, zig build test, zig build check-fat-image, and a sequential
QEMU sweep — vfs, vfs-client-death (the park/hold-handle path), fat-mount, log-flush,
orderly-shutdown, initial-ramdisk (log-flush silent in the bare sweep), smoke, init,
usb-storage, device-manager — all green.
Add a FAT12/16/32 filesystem the VFS mounts at /mnt/usb, reading and writing a
USB stick through the block device. Verified end to end under QEMU: the fat
server mounts the volume, the VFS routes /mnt/usb to it, and a client lists the
root and reads a file (the ELF magic of /mnt/usb/system/kernel).
- engine.zig: the FAT engine over a BlockDevice interface — mount (a bare FAT or,
as QEMU's VVFAT and most real sticks present it, an MBR-partitioned disk), FAT
chain walk (12/16/32), cluster allocation, directory traversal with long-name
read, and file read / write / create. Host-tested against a RAM-backed FAT16
image (create, cluster-spanning write, mid-file overwrite, read-back, list).
- on-disk.zig: the align(1) boot-sector / directory / long-name / FSInfo structs
and the cluster-count FAT-type detection.
- fat.zig: the server — wraps the .block device (a DMA bounce buffer) in a
BlockDevice, mounts the FAT, serves the vfs-protocol as a backend, and mounts
itself into the VFS at /mnt/usb. Spawned by init as a boot service.
- runtime.block: the block-device client (geometry / read / write by physical
address, so whole sectors never cross IPC).
- Raise the kernel service-name registry (maximum_services) 8 -> 16: it is
indexed directly by ServiceId, and fat = 8 was being rejected, so the fat
server exited before registering.
- VFS: an absolute path with no matching mount is now not-found rather than
silently created in the flat ramfs — so /mnt/usb fails cleanly until mounted.
Tests: fat-mount (the full stack: block -> FAT -> VFS mount -> list + file read)
passes; host units cover the engine and on-disk structs; the vfs, shutdown, and
USB regression suite stays green (10/10).
Daniel Samson