Test Case: LZ4 ztailpacking Edge Cases

Test ID: TC092-ztailpacking-edge

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: Medium
Regression: None

Objective

Verify correct handling of edge cases in ztailpacking (compressed tail packing) feature.

Preconditions

Generated image: images/lz4-ztail.erofs
Test files:
- /exact-pcluster.dat (4096-byte non-tail control)
- /one-byte-tail.dat (4097-byte logical boundary case)
- /max-tail.dat (8191-byte logical boundary case)
- /zero-tail.dat (empty-file control)
/inline.dat is independently proven by the manifest to have Z_EROFS_ADVISE_INLINE_PCLUSTER and nonzero h_idata_size. The four edge controls must not be described as ztailpacked unless their own map headers prove it.
Mount point: /mnt/test

Test Steps

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

Read file with exact pcluster size (no tail):

cat /mnt/test/files/exact-pcluster.dat > /tmp/out1
sha256sum /tmp/out1

Read file with minimal tail (1 byte):

cat /mnt/test/files/one-byte-tail.dat > /tmp/out2
tail -c 1 /tmp/out2 | od -A n -t x1

Read file with maximum tail size:

cat /mnt/test/files/max-tail.dat > /tmp/out3
stat -f %z /tmp/out3

Read file with zero-length tail:

cat /mnt/test/files/zero-tail.dat > /tmp/out4

Expected Results

Step 2: File without tail read correctly
Steps 2-5: Every exact logical size, full SHA256, and byte comparison matches its source file

Verification Method

Verify all tail size edge cases handled
Confirm boundary conditions don't cause errors
Test tail packing storage limits enforced correctly
Verify data integrity for all edge cases

Cleanup

umount /mnt/test
mdconfig -d -u "${unit#md}"
rm /tmp/out*

Notes

Tail size limits depend on inline storage capacity
Zero-length tail is valid edge case
Exact pcluster alignment means no tail needed
Related tests: TC091 (basic ztailpacking)

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