Two release blockers, both in the most destructive operation the package performs.
1. An unreadable /etc/fstab was treated as an empty one.
let content = fs::read_to_string(fstab_path).unwrap_or_default();
PermissionDenied, an I/O error, a damaged filesystem and "file absent" all collapsed
into an empty string. The rewrite then emitted a fstab containing only the managed swap
line and installed it atomically and successfully, dropping the root and boot mounts.
Consequence: a host that does not boot, guarded by one unwrap_or_default. The same
masking was present in read_fstab_swap_entries, so an unreadable fstab was reported by
status as "no swap entries", which reads as healthy drift-free state.
2. The backup was best-effort.
let _ = fs::write(bak_path, &content);
If it failed, the rewrite proceeded anyway. IMPLEMENTATION_SPEC and the acceptance
checklist both asserted the backup exists. The scenario where the backup fails is
exactly the scenario where it is needed.
New module fstab.rs owns the operation:
- read_required distinguishes NotFound from every other error and fails on both. A
missing /etc/fstab on Debian is an anomaly, not a blank slate, so it is never created;
- a blank candidate is refused outright;
- the backup is mandatory and flushed before the temp file is created, so there is no
window where the target is about to be replaced and no recovery copy exists;
- two copies are kept: .awg2-harness.bak is the state before the current rewrite,
.awg2-harness.original is written once with create_new and holds the host as it was
before this package first touched it;
- the temp file is a sibling of the target, created with create_new, sync_all'd, and
inherits the original permissions; a stale temp from a killed run is removed explicitly
rather than reused;
- the candidate is validated with findmnt --verify --tab-file before the swap. The step is
skipped when findmnt cannot be spawned; a rejection is fatal;
- commit is an atomic rename followed by a directory fsync;
- after the rename the target is re-read and compared to what was written. A mismatch
restores the backup and fails.
Also fixed: render_fstab_line interpolated the path raw. fstab fields are
whitespace-separated, so a space or tab in swap.path would shift every following column.
Paths now go through octal escaping (\040, \011, \012, \134).
Ten tests, all portable - the "unreadable but present" case is exercised by pointing the
reader at a directory, which fails as a non-NotFound error on every platform. Covered:
unreadable target is an error rather than an empty file, missing target is an error,
backup failure leaves the target byte-identical, blank candidate refused, unchanged
candidate is a no-op that writes no backup, the pristine copy survives repeated rewrites,
a stale temp does not block commit, and field escaping.
Docs updated: IMPLEMENTATION_SPEC section 17 gained the full rewrite contract, the
acceptance checklist gained seven checks including the two failure modes above.
cargo test --workspace: 124 + 4 passed, ten new. clippy -D warnings clean.
founder
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