Add LZ4 decompression support for full lcluster layout#36
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Adds read support for LZ4-compressed EROFS images using the full (legacy) lcluster index layout. Compact layout, ztailpacking, fragments, big_pcluster_2, HEAD2 / LZMA / DEFLATE / Zstd remain deferred — they return clear ErrNotImplemented at read time. New internal/zerofs package owns the z_erofs read path: map-header parsing & validation, full-layout lcluster decoding, pcluster resolution (preroll + big_pcluster_1), and a partial LZ4 block decoder that handles the EROFS LZ4_0Padding variant (leading zero inputmargin + stop-at-output-cap semantics, equivalent to the kernel's LZ4_decompress_safe_partial). erofs.go gains parseComprCfgs, loadCompressedBlock, an image-level pcluster LRU, and the superblock check is relaxed: the ComprAlgs field is now correctly treated as a union (lz4_max_distance pre- COMPR_CFGS, an algorithm bitmap when COMPR_CFGS is set). Tests cover the standard TestCases run through an LZ4 converter, compressibility edge cases, multi-pcluster spanning reads, plain-vs- LZ4 cross-validation, fuzz of compressed image bytes, and a deferred-feature check asserting compact-layout images error cleanly. Assisted-by: Claude Opus 4.7 <noreply@anthropic.com> Signed-off-by: Paul Meyer <katexochen0@gmail.com>
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This is the first in a series of patches adding compression support. I tried t split this into revieweable chunks that work as stand-alone additions.
Adds read support for LZ4-compressed EROFS images using the full (legacy) lcluster index layout. Compact layout, ztailpacking, fragments, big_pcluster_2, HEAD2 / LZMA / DEFLATE / Zstd remain deferred — they return clear ErrNotImplemented at read time.
New internal/zerofs package owns the z_erofs read path: map-header parsing & validation, full-layout lcluster decoding, pcluster resolution (preroll + big_pcluster_1), and a partial LZ4 block decoder that handles the EROFS LZ4_0Padding variant (leading zero inputmargin + stop-at-output-cap semantics, equivalent to the kernel's LZ4_decompress_safe_partial).
erofs.go gains parseComprCfgs, loadCompressedBlock, an image-level pcluster LRU, and the superblock check is relaxed: the ComprAlgs field is now correctly treated as a union (lz4_max_distance pre- COMPR_CFGS, an algorithm bitmap when COMPR_CFGS is set).
Tests cover the standard TestCases run through an LZ4 converter, compressibility edge cases, multi-pcluster spanning reads, plain-vs- LZ4 cross-validation, fuzz of compressed image bytes, and a deferred-feature check asserting compact-layout images error cleanly.