54 lines
1.6 KiB
Markdown
54 lines
1.6 KiB
Markdown
# Test Case: LZ4 Deterministic Random-Offset Reads
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**Test ID**: TC087-lz4-random-read
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**G5 fixture contract**: Use [G5-MANUAL-SETUP.md](G5-MANUAL-SETUP.md).
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Its generated paths, source comparisons, structured corruption offsets, and
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cleanup rules supersede placeholder examples in this file.
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**Category**: Compression
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**Priority**: High
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## Objective
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Verify non-sequential reads from deterministic offsets in an LZ4-compressed
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file and compare every returned byte with the source. `$RANDOM` and timing-only
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checks are not evidence of data correctness.
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## Fixture and Helper
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```sh
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work=$(mktemp -d /tmp/repo22-tc087.XXXXXX)
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tests/prepare_error_fixtures.sh "$work/fixtures"
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cc -O2 -Wall -Wextra -std=c17 tests/read_probe.c -o "$work/read_probe"
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dump.erofs --path=/compressed.bin -e "$work/fixtures/valid-lz4.erofs"
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```
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## FreeBSD Procedure
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```sh
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mkdir "$work/mnt"
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unit=$(mdconfig -a -t vnode -f "$work/fixtures/valid-lz4.erofs")
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mount -t erofs -o ro "/dev/$unit" "$work/mnt"
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size=$(stat -f %z "$work/fixtures/source/compressed.bin")
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test "$size" -gt 1052672
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index=0
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for offset in 0 4096 65536 1048576 $((size - 4096)); do
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"$work/read_probe" pread "$work/mnt/compressed.bin" \
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"$offset" 4096 "$work/guest-$index.bin"
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"$work/read_probe" pread "$work/fixtures/source/compressed.bin" \
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"$offset" 4096 "$work/source-$index.bin"
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cmp "$work/source-$index.bin" "$work/guest-$index.bin"
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index=$((index + 1))
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done
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umount "$work/mnt"
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mdconfig -d -u "${unit#md}"
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```
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## Expected Results
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All five fixed reads, including the final 4 KiB of the file, return exactly
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4096 bytes and compare equal to their corresponding source ranges. No
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performance ordering is asserted.
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