Test Case: LZ4 ztailpacking Data Path

Test ID: TC091-ztailpacking-basic

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 operation of ztailpacking (compressed tail packing) for LZ4-compressed files.

Preconditions

EROFS image with ztailpacking enabled: test-ztailpacking.erofs
Test file: /inline.dat (64KB deterministic compressible data)
Mount point: /mnt/test

Generate with:

mkfs.erofs -zlz4 -C4096 -Eztailpacking test-ztailpacking.erofs source

Before mounting, require dump.erofs -s to report ztailpacking and dump.erofs --path=/inline.dat -e to show the compressed physical extent inside the metadata block. Enabling the mkfs option alone does not prove that the target file was tail-packed.

Test Steps

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

Read file with packed tail:

cat /mnt/test/inline.dat > /tmp/output.dat

Verify file size correct:
```
stat -f %z /mnt/test/inline.dat
```

Read file tail specifically:

tail -c 1024 /mnt/test/inline.dat > /tmp/tail.dat

Verify data integrity:
```
sha256 /tmp/output.dat
```

Expected Results

Step 2: File read successfully with tail decompressed
Step 3: Size matches original uncompressed size
Step 4: Tail data correct
Step 5: Checksum matches reference

Verification Method

Verify tail-packed data decompressed correctly
Confirm storage efficiency (tail stored inline or in special area)
Test tail packing transparent to reader
Verify boundary between main data and packed tail handled correctly

Cleanup

umount /mnt/test
mdconfig -d -u md0
rm /tmp/output.dat /tmp/tail.dat

Notes

ztailpacking stores compressed file tail inline with inode or in special area
Reduces fragmentation and improves small file efficiency
Related tests: TC092 (edge cases), TC033 (uncompressed tailpacking)

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