Test Case: LZ4 Compressed File Read

Test ID: TC003-lz4-compressed-read

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: Critical
Regression: None

Objective

Verify correct decompression and reading of LZ4-compressed files.

Preconditions

EROFS image with LZ4-compressed files: test-lz4.erofs
Known reference file: original.txt (uncompressed source)
Compressed file in image: /compressed/test.txt
Mount point: /mnt/test

Test Steps

Mount the LZ4 test image:
```
mount -t erofs /dev/md0 /mnt/test
```
Verify file exists:
```
ls -lh /mnt/test/compressed/test.txt
```

Read the entire file:

cat /mnt/test/compressed/test.txt > /tmp/decompressed.txt

Calculate checksum:

sha256 /tmp/decompressed.txt
sha256 original.txt

Compare byte-for-byte:
```
cmp /tmp/decompressed.txt original.txt
```

Test partial read:

dd if=/mnt/test/compressed/test.txt of=/tmp/partial.txt bs=1024 count=1

Verify partial read matches:

cmp -n 1024 /tmp/partial.txt original.txt

Expected Results

Step 1: Mount succeeds
Step 2: File size matches original uncompressed size
Step 4: SHA256 checksums are identical
Step 5: cmp returns 0 (files identical)
Step 7: First 1024 bytes match

Verification Method

Exact byte-for-byte match with original file
No corruption in decompressed data
File attributes (size, timestamps) preserved correctly

Check inode compression format:

# Using custom debug tool if available
erofs_inspect /dev/md0 /compressed/test.txt
# Should show: z_algorithmformat[0:2] = Z_EROFS_COMPRESSION_LZ4

Cleanup

umount /mnt/test
mdconfig -d -u md0
rm /tmp/decompressed.txt /tmp/partial.txt

Notes

LZ4 is the most common compression algorithm in EROFS
Test should cover files of various sizes: small (<4KB), medium (4KB-1MB), large (>1MB)
LZ4 pcluster size is typically 4KB or 64KB
Related: TC004 (ztailpacking), TC005 (pcluster mapping)

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