erofs-freebsd-out-tree/tests/TC087-lz4-random-read.md

Test Case: LZ4 Deterministic Random-Offset Reads

Test ID: TC087-lz4-random-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: High

Objective

Verify non-sequential reads from deterministic offsets in an LZ4-compressed file and compare every returned byte with the source. $RANDOM and timing-only checks are not evidence of data correctness.

Fixture and Helper

work=$(mktemp -d /tmp/repo22-tc087.XXXXXX)
tests/prepare_error_fixtures.sh "$work/fixtures"
cc -O2 -Wall -Wextra -std=c17 tests/read_probe.c -o "$work/read_probe"
dump.erofs --path=/compressed.bin -e "$work/fixtures/valid-lz4.erofs"

FreeBSD Procedure

mkdir "$work/mnt"
unit=$(mdconfig -a -t vnode -f "$work/fixtures/valid-lz4.erofs")
mount -t erofs -o ro "/dev/$unit" "$work/mnt"
size=$(stat -f %z "$work/fixtures/source/compressed.bin")
test "$size" -gt 1052672

index=0
for offset in 0 4096 65536 1048576 $((size - 4096)); do
  "$work/read_probe" pread "$work/mnt/compressed.bin" \
    "$offset" 4096 "$work/guest-$index.bin"
  "$work/read_probe" pread "$work/fixtures/source/compressed.bin" \
    "$offset" 4096 "$work/source-$index.bin"
  cmp "$work/source-$index.bin" "$work/guest-$index.bin"
  index=$((index + 1))
done

umount "$work/mnt"
mdconfig -d -u "${unit#md}"

Expected Results

All five fixed reads, including the final 4 KiB of the file, return exactly 4096 bytes and compare equal to their corresponding source ranges. No performance ordering is asserted.