M6.5 Phase 5: Subsystem Contracts

Phase 5 validates kernel subsystem interfaces: device nodes and /proc filesystem.

/dev/zero implementation

Kevlar's devfs had /dev/null but was missing /dev/zero. Added kernel/fs/devfs/zero.rs — a simple character device that returns infinite zeros on read and absorbs all writes. The implementation uses UserBufWriter::write_with() to fill the user buffer with slice.fill(0).

Tests

dev_null_zero — Validates /dev/null (write succeeds, read returns EOF) and /dev/zero (read returns all zeros).

proc_self — Validates /proc/self/exe (readlink returns executable path) and /proc/self/stat (contains pid (comm) state in the expected Linux format with a valid state character).

Known gaps

  • /proc/cpuinfo format validation: not tested yet (needed for M7)
  • /proc/[pid]/maps format: not tested yet
  • /sys hierarchy: not implemented
  • DRM devices: not implemented (M10 scope)
  • /dev/urandom: not implemented (getrandom syscall works instead)

Results

Full suite: 17/18 PASS (only sa_restart TIMEOUT remains).