Test Case: LZ4 Compressed Physical Cluster Mapping (4KB)

Test ID: TC089-lz4-pcluster-4k

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

Objective

Verify correct physical cluster (pcluster) mapping for LZ4 compression with 4KB pcluster size.

Preconditions

EROFS image with LZ4, 4KB pcluster: test-lz4-pcluster-4k.erofs
Test file: /files/test-4k.dat (aligned to 4KB boundaries)
Mount point: /mnt/test

Test Steps

Mount the image:
```
mount -t erofs /dev/md0 /mnt/test
```

Read aligned to pcluster boundary (offset 0):

dd if=/mnt/test/files/test-4k.dat of=/tmp/out1 bs=4K count=1 skip=0

Read aligned to pcluster boundary (offset 4K):

dd if=/mnt/test/files/test-4k.dat of=/tmp/out2 bs=4K count=1 skip=1

Read unaligned (crosses pcluster boundary):

dd if=/mnt/test/files/test-4k.dat of=/tmp/out3 bs=2K count=2 skip=1

Read spanning multiple pclusters:

dd if=/mnt/test/files/test-4k.dat of=/tmp/out4 bs=16K count=1

Expected Results

Step 2: Single pcluster decompressed, correct data
Step 3: Adjacent pcluster decompressed, correct data
Step 4: Two pclusters decompressed for unaligned read
Step 5: Four pclusters decompressed (16K / 4K = 4)

Verification Method

Verify pcluster boundaries handled correctly
Confirm unaligned reads work (may decompress extra pclusters)
Test each pcluster independently decompressible
Verify correct data returned for all read patterns

Cleanup

umount /mnt/test
mdconfig -d -u md0
rm /tmp/out1 /tmp/out2 /tmp/out3 /tmp/out4

Notes

4KB pcluster provides good random access performance
Each 4KB logical region compressed independently
Small pcluster = less compression, better random access
Related tests: TC090 (64KB pcluster)

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