# Test Case: Mount Error Conditions

**Test ID**: TC008-mount-errors
**Category**: Mount Operations
**Priority**: High

## Objective

Verify graceful rejection of three distinct provider conditions: a
checksum-valid bad magic at the correct field, a 1023-byte provider ending
before the superblock, and a zero-length provider.

## Fixture Qualification

```sh
work=$(mktemp -d /tmp/repo22-tc008.XXXXXX)
tests/prepare_error_fixtures.sh "$work/fixtures"
grep -E '^(bad-magic|truncated-before-super|empty-provider) ' \
  "$work/fixtures/fixture-evidence.txt"
python3 tests/erofs_fixture.py inspect "$work/fixtures/bad-magic.erofs"
wc -c "$work/fixtures/bad-magic.erofs" \
  "$work/fixtures/truncated-before-super.erofs" \
  "$work/fixtures/empty-provider.erofs"
(cd "$work/fixtures" && sha256 -c SHA256SUMS)
```

The bad-magic variant changes only absolute bytes 1024 through 1027 and
preserves media size. It intentionally retains the original checksum: the
production verifier's fixed-magic suffix calculation remains valid, while the
canonical checksum over the now-invalid magic does not. Magic is rejected
before checksum verification. The short and empty fixtures are intentional
provider-size cases, not same-size corruption variants.

## FreeBSD Procedure

Create a fresh mount directory. Execute each case separately and record whether
failure occurs at `mdconfig` or `nmount`; never assume a fixed md number.

```sh
mkdir "$work/mnt"
for image in bad-magic.erofs truncated-before-super.erofs empty-provider.erofs
do
  set +e
  unit=$(mdconfig -a -t vnode -f "$work/fixtures/$image" \
    2>"$work/$image.md.err")
  md_status=$?
  set -e
  printf '%s md_status=%s unit=%s\n' "$image" "$md_status" "$unit"
  if test "$md_status" -eq 0; then
    set +e
    mount -t erofs -o ro "/dev/$unit" "$work/mnt" \
      >"$work/$image.out" 2>"$work/$image.mount.err"
    mount_status=$?
    set -e
    printf '%s mount_status=%s\n' "$image" "$mount_status"
    test "$mount_status" -ne 0
    set +e
    truss -o "$work/$image.mount.truss" mount -t erofs -o ro \
      "/dev/$unit" "$work/mnt" >/dev/null 2>&1
    set -e
    grep -E 'nmount.*ERR#' "$work/$image.mount.truss"
    mdconfig -d -u "${unit#md}"
  else
    cat "$work/$image.md.err"
  fi
  ! mount -p | awk -v path="$work/mnt" '$2 == path { found=1 }
    END { exit found ? 0 : 1 }'
done
```

## Expected Results

All three cases fail without panic or hang. Bad magic reaches `nmount` and
returns `EINVAL`. A 1023-byte vnode provider reaches `nmount` and returns
`ENXIO`; a zero-byte provider is rejected by `mdconfig` with `EINVAL`. Record
the observed stage and errno rather than fabricating a mount result. No md unit
or mount may remain after each case.