The first CUBE code in the kernel, and deliberately only a reader: the write
authority has not moved yet, and PLAN-kernel-cubelinux.md records both that
decision and the hazard that makes the order matter — a kernel writing while a
userspace daemon still holds the same image loses one of the two writers' work,
silently. A reader cannot do that.
- drivers/cube/: a Rust module exposing /dev/cubelinux. Reading it reads the
pinned image from the block device through the kernel's own file layer
(filp_open + kernel_read — the path this kernel version binds for Rust, and
the reason no C helper was needed), parses the records, and returns one line:
digest curve=0 bytes=8400896 records=35318 value_bytes=6139148 fnv1a64=5e20f98455387b08 errors=0
The work happens on read, not at init, so there is no initcall ordering to get
wrong against the block driver that provides the device.
- The format is restated in the kernel (32-byte space, 24-byte key, 8-byte LE
length, value), including the two rules the userspace parser documents: a value
that runs past the buffer is a truncated record, and an all-zero frame ends the
records only when every remaining byte is zero — the rule that keeps a real
record at the origin from being read as padding.
- The digest is the point. A record count alone lets two different images agree;
folding the bytes in means the kernel and userspace are *compared* rather than
assumed to agree. `cube-image digest` prints the same line in the same field
order, and the QEMU gate fails if they differ by a byte.
Gate, on both images:
curated 11 records, 4,096 bytes, fnv1a64=161113085b1573b2 — match
snapshot 35,318 records, 8,400,896 bytes, fnv1a64=5e20f98455387b08 — match
The tree carries CONFIG_CUBELINUX_STORE=y on top of defconfig + RUST; a tree
without it boots and simply has no /dev/cubelinux.
CUBELinux build