erofs-freebsd-out-tree/docs/pre12-batch-06.md

Pre-12 Batch 06: codec descriptor ownership

Date: 2026-08-13

Scope

• Moved the LZMA, DEFLATE, and ZSTD descriptors into their backend source files.
• Made their backend-only config, decompress, and availability helpers static.
• Kept the LZ4 config loader and descriptor, plus the SHIFTED and INTERLACED descriptors and transform, in src/decompressor.c.
• Replaced the central descriptor object array with the descriptor pointer table z_erofs_decomp.
• Reduced src/compress.h to the three backend descriptor declarations and the LZ4 decompress prototype needed by the central descriptor.

Descriptor tuples

The normalized tuples are unchanged before and after this batch:

Index	Name	Config callback	Decompress callback	Compile condition
Z_EROFS_COMPRESSION_LZ4	lz4	z_erofs_load_lz4_config	z_erofs_lz4_decompress	always
Z_EROFS_COMPRESSION_LZMA	lzma	z_erofs_load_lzma_config	z_erofs_lzma_decompress	always
Z_EROFS_COMPRESSION_DEFLATE	deflate	z_erofs_load_deflate_config	z_erofs_deflate_decompress	always
Z_EROFS_COMPRESSION_ZSTD	zstd	z_erofs_load_zstd_config	z_erofs_zstd_decompress	descriptor and config always; decompress implementation selected by ZSTDIO
Z_EROFS_COMPRESSION_SHIFTED	shifted	NULL	z_erofs_transform_plain	always
Z_EROFS_COMPRESSION_INTERLACED	interlaced	NULL	z_erofs_transform_plain	always

Static validation

• Confirmed one declaration and one definition for each backend descriptor; the only additional occurrence is its central pointer-table entry.
• Confirmed the LZMA and DEFLATE config/decompress helpers have no external consumers and are now static in their backends.
• Confirmed the ZSTD config/decompress/availability helpers have no external consumers and are now static; the two decompress definitions are mutually exclusive under #ifdef ZSTDIO.
• Confirmed z_erofs_decomp explicitly fills all six runtime indices in the original order. Decompression retains the array-length bound, rejects a null table entry, and rejects a null decompress callback with EOPNOTSUPP. Config parsing retains the existing compression-config loop bound and treats a null entry or null config callback as EOPNOTSUPP before releasing the config buffer on the existing path.
• Confirmed the WITH_ZSTDIO=0 static conditional path remained valid; actual build deferred to final validation. Without ZSTDIO, the path keeps the descriptor non-null, reports the existing mount error and EOPNOTSUPP from config, and selects the decompress stub returning -1.
• Confirmed WITH_ZSTDIO=1 adds -DZSTDIO, keeps the same descriptor and config callback, and selects the existing ZSTD implementation with its resource-release and error paths unchanged.
• git diff --check and git diff --cached --check were required for this batch.

Deferred validation

No build, QEMU, smoke, feature, or other dynamic validation was run for this batch. Follow-up validation must build the FreeBSD KLD with both WITH_ZSTDIO=0 and WITH_ZSTDIO=1.