Test Case: LZ4 Compressed Physical Cluster Mapping (64KB)

Test ID: TC090-lz4-pcluster-64k

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 mapping for LZ4 compression with 64KB pcluster size.

Preconditions

EROFS image with LZ4, 64KB pcluster: test-lz4-pcluster-64k.erofs
Test file: /files/test-64k.dat (1MB, highly compressible)
Mount point: /mnt/test
Generate with mkfs.erofs -zlz4 -C65536 test-lz4-pcluster-64k.erofs source and confirm compr_cfgs big_pcluster with dump.erofs -s.

Test Steps

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

Read first pcluster (64KB):

dd if=/mnt/test/files/test-64k.dat of=/tmp/out1 bs=64K count=1

Read small portion requiring full pcluster decompression:

dd if=/mnt/test/files/test-64k.dat of=/tmp/out2 bs=4K count=1 skip=1

Read crossing pcluster boundary:

dd if=/mnt/test/files/test-64k.dat of=/tmp/cross bs=1 skip=65504 count=64
dd if=/root/reference/test-64k.dat of=/tmp/cross.expected bs=1 skip=65504 count=64
cmp /tmp/cross /tmp/cross.expected

Record the physical extent layout:

dump.erofs --path=/files/test-64k.dat -e test-lz4-pcluster-64k.erofs

Expected Results

Step 2: Full 64KB pcluster decompressed correctly
Step 3: Reading 4KB requires decompressing entire 64KB pcluster
Step 4: Boundary crossing handled correctly
Step 5: The fixture contains a real compressed big-pcluster extent

Verification Method

Verify large pcluster decompression works
Confirm small reads still trigger full pcluster decompression
Test memory usage reasonable for 64KB decompression
Do not require a better compression ratio than 4KB for every corpus

Cleanup

umount /mnt/test
mdconfig -d -u md0
rm /tmp/out* /tmp/cross /tmp/cross.expected

Notes

64KB pcluster provides better compression at cost of random access
Common pcluster size for read-heavy workloads
Related tests: TC089 (4KB pcluster), TC088 (config handling)

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