# Test Case: LZ4 Compression Configuration Handling

**Test ID**: TC088-lz4-config-handling  

**G5 fixture contract**: Use [G5-MANUAL-SETUP.md](G5-MANUAL-SETUP.md).
Its generated paths, source comparisons, structured corruption offsets, and
cleanup rules supersede placeholder examples in this file.
**Category**: Compression  
**Priority**: Medium  
**Regression**: None

## Objective
Verify correct handling of different LZ4 compression configurations.

## Preconditions
- Multiple EROFS images with different LZ4 configs:
  - `lz4-pcluster-4k.erofs` (4KB pcluster)
  - `lz4-pcluster-64k.erofs` (64KB pcluster)
  - `lz4-pcluster-256k.erofs` (256KB pcluster)
- Test file in each: `/files/test.dat` (identical content)
- Mount points: `/mnt/test1`, `/mnt/test2`, `/mnt/test3`
- Generate the images explicitly with `mkfs.erofs 1.8.6`:
  ```
  mkfs.erofs -zlz4 -C4096 lz4-pcluster-4k.erofs source
  mkfs.erofs -zlz4 -C65536 lz4-pcluster-64k.erofs source
  mkfs.erofs -zlz4 -C262144 lz4-pcluster-256k.erofs source
  ```
- Confirm the requested feature/configuration with `dump.erofs -s` before
  treating an image as a valid fixture.

## Test Steps
1. Mount all three images:
   ```
   mount -t erofs /dev/md0 /mnt/test1
   mount -t erofs /dev/md1 /mnt/test2
   mount -t erofs /dev/md2 /mnt/test3
   ```

2. Read from each and verify identical output:
   ```
   sha256 /mnt/test1/files/test.dat
   sha256 /mnt/test2/files/test.dat
   sha256 /mnt/test3/files/test.dat
   ```

3. Record image sizes without assuming a monotonic compression ratio:
   ```
   stat -f %z /root/lz4-pcluster-4k.erofs
   stat -f %z /root/lz4-pcluster-64k.erofs
   stat -f %z /root/lz4-pcluster-256k.erofs
   ```

4. Verify the same offset read with each pcluster size. Timing is diagnostic
   only and is not a functional pass criterion:
   ```
   time dd if=/mnt/test1/files/test.dat of=/dev/null bs=4K skip=100 count=10
   time dd if=/mnt/test2/files/test.dat of=/dev/null bs=4K skip=100 count=10
   time dd if=/mnt/test3/files/test.dat of=/dev/null bs=4K skip=100 count=10
   ```

## Expected Results
- Step 1: All mounts succeed
- Step 2: All three checksums identical (data integrity)
- Step 3: Image sizes are recorded for the exact corpus and mkfs version
- Step 4: All reads succeed and return identical data at the tested offset

## Verification Method
- Verify all pcluster configurations work correctly
- Record pcluster size effects without assuming they are monotonic for every
  corpus or under a QEMU TCG guest
- Test driver handles different configs transparently

## Cleanup
```
umount /mnt/test1 /mnt/test2 /mnt/test3
mdconfig -d -u "${unit1#md}"
mdconfig -d -u "${unit2#md}"
mdconfig -d -u "${unit3#md}"
```

## Notes
- Pcluster size is compression unit (physical cluster)
- Larger pcluster -> better compression, worse random access
- Typical sizes: 4KB, 16KB, 64KB, 256KB
- Related tests: TC089 (pcluster mapping)
