# Test Case: Chunk Indexes and Compressed Pcluster on External Slots

**Test ID**: TC094-chunk-multi-device  
**Category**: Chunk-Based / Multi-Device
**Priority**: Critical

## Objective

Verify alternating external chunk slots, a nonzero device ID with
`uniaddr=0`, provider identity, and a real external two-block LZ4 pcluster.

## Fixture qualification

Use the fresh G6 artifacts and manifest:

- `multi2-*`: `/cross-device.bin` has three 131072-byte chunks with device IDs
  `1,2,1`; slot blocks differ, so provider swapping fails deterministically.
- `multi2-uniaddr0-*`: slot 1 has `uniaddr=0`, but indexes retain device ID 1.
- `lz4-external-pcluster-*`: the original fixed 8192-byte LZ4 pcluster is
  fsck-qualified before relocation.  The generated primary is only 8192 bytes,
  contains metadata plus the table, and has HEAD pblk `2`; both compressed
  blocks exist only in slot 1.

## Alternating slots and provider identity

```sh
I=/root/repo22-g6/images
S=/root/repo22-g6/sources/chunk
mkdir -p /mnt/g6
kldload /root/repo22-g6/erofs.ko
mdconfig -a -t vnode -f "$I/multi2-primary.erofs" -u 90
mdconfig -a -t vnode -f "$I/multi2-slot1.blob" -u 91
mdconfig -a -t vnode -f "$I/multi2-slot2.blob" -u 92
mount -t erofs -o ro -o device.2=/dev/md92 -o device.1=/dev/md91 \
  /dev/md90 /mnt/g6
cmp "$S/cross-device.bin" /mnt/g6/cross-device.bin
sha256 "$S/cross-device.bin" /mnt/g6/cross-device.bin
dd if="$S/cross-device.bin" of=/tmp/tc094.expected bs=1 skip=126976 count=8192 2>/dev/null
dd if=/mnt/g6/cross-device.bin of=/tmp/tc094.actual bs=1 skip=126976 count=8192 2>/dev/null
cmp /tmp/tc094.expected /tmp/tc094.actual
for off in 0 131072 262144; do
  dd if="$S/cross-device.bin" of=/tmp/tc094.src.$off bs=1 skip=$off count=4096 2>/dev/null
  dd if=/mnt/g6/cross-device.bin of=/tmp/tc094.mnt.$off bs=1 skip=$off count=4096 2>/dev/null
  cmp /tmp/tc094.src.$off /tmp/tc094.mnt.$off
done
umount /mnt/g6
mdconfig -d -u 92
mdconfig -d -u 91
mdconfig -d -u 90
```

Confirm swapped providers fail with `ENXIO`:

```sh
mdconfig -a -t vnode -f "$I/multi2-primary.erofs" -u 90
mdconfig -a -t vnode -f "$I/multi2-slot1.blob" -u 91
mdconfig -a -t vnode -f "$I/multi2-slot2.blob" -u 92
truss -f -o /tmp/tc094-swap.truss mount -t erofs -o ro \
  -o device.1=/dev/md92 -o device.2=/dev/md91 /dev/md90 /mnt/g6
tail -20 /tmp/tc094-swap.truss
mdconfig -d -u 92
mdconfig -d -u 91
mdconfig -d -u 90
```

## Zero unified address with explicit device ID

```sh
mdconfig -a -t vnode -f "$I/multi2-uniaddr0-primary.erofs" -u 90
mdconfig -a -t vnode -f "$I/multi2-uniaddr0-slot1.blob" -u 91
mdconfig -a -t vnode -f "$I/multi2-uniaddr0-slot2.blob" -u 92
mount -t erofs -o ro -o device.2=/dev/md92 -o device.1=/dev/md91 \
  /dev/md90 /mnt/g6
cmp "$S/cross-device.bin" /mnt/g6/cross-device.bin
umount /mnt/g6
mdconfig -d -u 92
mdconfig -d -u 91
mdconfig -d -u 90
```

## External compressed pcluster

```sh
P=/root/repo22-g6/sources/pcluster
mdconfig -a -t vnode -f "$I/lz4-external-pcluster-primary.erofs" -u 90
mdconfig -a -t vnode -f "$I/lz4-external-pcluster-slot1.blob" -u 91
mount -t erofs -o ro -o device.1=/dev/md91 /dev/md90 /mnt/g6
stat -f '%z' /mnt/g6/external-pcluster.bin
sha256 "$P/external-pcluster.bin" /mnt/g6/external-pcluster.bin
cmp "$P/external-pcluster.bin" /mnt/g6/external-pcluster.bin
dd if="$P/external-pcluster.bin" of=/tmp/tc094-p.src bs=1 skip=61440 count=8192 2>/dev/null
dd if=/mnt/g6/external-pcluster.bin of=/tmp/tc094-p.mnt bs=1 skip=61440 count=8192 2>/dev/null
cmp /tmp/tc094-p.src /tmp/tc094-p.mnt
truss -f -o /tmp/tc094-p-ebusy.truss mdconfig -d -u 91
tail -20 /tmp/tc094-p-ebusy.truss
```

The 131072-byte output must match although the primary has no old compressed
extent; normal slot detach must return `EBUSY`.

## Cleanup and zero-state check

```sh
umount /mnt/g6
mdconfig -d -u 91
mdconfig -d -u 90
kldunload erofs
rm -f /tmp/tc094.expected /tmp/tc094.actual /tmp/tc094.src.* \
  /tmp/tc094.mnt.* /tmp/tc094-p.src /tmp/tc094-p.mnt
mount -p | awk '$3 == "erofs" { print }'
mdconfig -l
kldstat -n erofs 2>/dev/null || true
sysctl -n kern.geom.conftxt | grep -E 'md9[0-2]|erofs' || true
```

All four final outputs must be empty, with no panic, trap, or hang.