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tests/TC095-chunk-index-read.md

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+# Test Case: Chunk Index Decode and Mapped Device ID
+
+**Test ID**: TC095-chunk-index-read  
+**Category**: Chunk-Based  
+**Priority**: High
+
+## Objective
+
+Verify first/middle/last 8-byte indexes, zero-high and nonzero-high 48-bit
+decode, the rounded device-ID mask, and `ENODEV` for mapped ID 3.
+
+## Field qualification
+
+After G6 generation, print the fields on the host that will be exercised:
+
+```sh
+OUTPUT=/path/to/generated-fixtures
+python3 -B - "$OUTPUT/manifest.json" <<'PY'
+import json, sys
+m = json.load(open(sys.argv[1]))
+for fixture in ('multi2', 'multi2-unified48', 'bad-mapped-device3'):
+    c = m['fixtures'].get(fixture, {}).get('image', {}).get('chunks', {})
+    if '/indexed.bin' in c:
+        print(fixture, c['/indexed.bin'])
+print(m['mutations'])
+PY
+```
+
+The normal `indexed.bin` has five 32768-byte indexes with IDs `1,2,1,2,1`.
+The 48-bit control has format bit `0x40` with zero high words; its unified
+target also contains a real nonzero high word.  The negative second index is
+exactly device ID 3 while `extra_devices=2`, whose mask is 3.
+
+## Normal and cross-index reads
+
+```sh
+I=/root/repo22-g6/images
+S=/root/repo22-g6/sources/chunk
+mkdir -p /mnt/g6
+kldload /root/repo22-g6/erofs.ko
+mdconfig -a -t vnode -f "$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.1=/dev/md91 -o device.2=/dev/md92 \
+  /dev/md90 /mnt/g6
+cmp "$S/indexed.bin" /mnt/g6/indexed.bin
+dd if="$S/indexed.bin" of=/tmp/tc095.first.src bs=1 skip=0 count=4096 2>/dev/null
+dd if=/mnt/g6/indexed.bin of=/tmp/tc095.first.mnt bs=1 skip=0 count=4096 2>/dev/null
+cmp /tmp/tc095.first.src /tmp/tc095.first.mnt
+dd if="$S/indexed.bin" of=/tmp/tc095.middle.src bs=1 skip=65536 count=4096 2>/dev/null
+dd if=/mnt/g6/indexed.bin of=/tmp/tc095.middle.mnt bs=1 skip=65536 count=4096 2>/dev/null
+cmp /tmp/tc095.middle.src /tmp/tc095.middle.mnt
+dd if="$S/indexed.bin" of=/tmp/tc095.last.src bs=1 skip=131072 count=4096 2>/dev/null
+dd if=/mnt/g6/indexed.bin of=/tmp/tc095.last.mnt bs=1 skip=131072 count=4096 2>/dev/null
+cmp /tmp/tc095.last.src /tmp/tc095.last.mnt
+dd if="$S/indexed.bin" of=/tmp/tc095.cross.src bs=1 skip=28672 count=8192 2>/dev/null
+dd if=/mnt/g6/indexed.bin of=/tmp/tc095.cross.mnt bs=1 skip=28672 count=8192 2>/dev/null
+cmp /tmp/tc095.cross.src /tmp/tc095.cross.mnt
+umount /mnt/g6
+mdconfig -d -u 92
+mdconfig -d -u 91
+mdconfig -d -u 90
+```
+
+## 48-bit indexes and high unified address
+
+```sh
+mdconfig -a -t vnode -f "$I/multi2-unified48-primary.erofs" -u 90
+mdconfig -a -t vnode -f "$I/multi2-unified48-slot1.blob" -u 91
+mdconfig -a -t vnode -f "$I/multi2-unified48-slot2.blob" -u 92
+mount -t erofs -o ro -o device.2=/dev/md92 -o device.1=/dev/md91 \
+  /dev/md90 /mnt/g6
+cmp "$S/indexed.bin" /mnt/g6/indexed.bin
+cmp "$S/unified-address.bin" /mnt/g6/unified-address.bin
+umount /mnt/g6
+mdconfig -d -u 92
+mdconfig -d -u 91
+mdconfig -d -u 90
+```
+
+## Mapped undeclared ID
+
+```sh
+mdconfig -a -t vnode -f "$I/bad-mapped-device3.erofs" -u 90
+mdconfig -a -t vnode -f "$I/multi2-slot1.blob" -u 91
+mdconfig -a -t vnode -f "$I/multi2-slot2.blob" -u 92
+mount -t erofs -o ro -o device.1=/dev/md91 -o device.2=/dev/md92 \
+  /dev/md90 /mnt/g6
+truss -f -o /tmp/tc095-enodev.truss dd if=/mnt/g6/indexed.bin \
+  of=/dev/null bs=1 skip=32768 count=4096
+tail -20 /tmp/tc095-enodev.truss
+cmp "$S/tc006.bin" /mnt/g6/tc006.bin
+```
+
+The affected read must return exactly `ENODEV`; the mount and unaffected file
+remain usable.
+
+## Cleanup and zero-state check
+
+```sh
+umount /mnt/g6
+mdconfig -d -u 92
+mdconfig -d -u 91
+mdconfig -d -u 90
+kldunload erofs
+rm -f /tmp/tc095.*.src /tmp/tc095.*.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.