Add support for long xattr prefix #1
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@@ -84,14 +84,140 @@ func EroFS(r io.ReaderAt) (fs.FS, error) { | |
| type image struct { | ||
| sb disk.SuperBlock | ||
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| meta io.ReaderAt | ||
| blkPool sync.Pool | ||
| longPrefixes []string // cached long xattr prefixes | ||
| prefixesOnce sync.Once | ||
| prefixesErr error | ||
| } | ||
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| func (img *image) blkOffset() int64 { | ||
| return int64(img.sb.MetaBlkAddr) << int64(img.sb.BlkSizeBits) | ||
| } | ||
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| // loadLongPrefixes loads and caches the long xattr prefixes from the superblock | ||
| func (img *image) loadLongPrefixes() error { | ||
| img.prefixesOnce.Do(func() { | ||
| if img.sb.XattrPrefixCount == 0 { | ||
| return | ||
| } | ||
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| // Long prefixes are stored in the packed inode, after the inode header | ||
| // The packed inode is typically a compact inode (32 bytes) | ||
| // Address = MetaBlkAddr + (PackedNid * 32) + inode_size + (XattrPrefixStart * 4) | ||
| // Note: XattrPrefixStart is in units of 4 bytes from the end of the packed inode | ||
| baseAddr := img.blkOffset() + int64(img.sb.PackedNid)*32 + 32 + int64(img.sb.XattrPrefixStart)*4 | ||
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There was a problem hiding this comment. The magic number 32 appears twice in this address calculation. Consider defining a constant like
Member
There was a problem hiding this comment. If long xattr prefixes are located in packed inode or metabox inode, I suggest just using regular inode read logic to read XattrPrefixStart*4 directly, instead of just read data after the inode metadata (because the packed inode can be compressed, or non-inline, etc.) |
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| img.longPrefixes = make([]string, img.sb.XattrPrefixCount) | ||
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| // We'll read the prefixes incrementally since they can be large | ||
| // and may span multiple blocks | ||
| currentAddr := baseAddr | ||
| var blk *block | ||
| var buf []byte | ||
| var err error | ||
| bufOffset := 0 // offset within the current buffer | ||
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| for i := 0; i < int(img.sb.XattrPrefixCount); i++ { | ||
| // Ensure we have at least 2 bytes to read the length | ||
| if blk == nil || bufOffset+2 > len(buf) { | ||
| if blk != nil { | ||
| img.putBlock(blk) | ||
| } | ||
| blk, err = img.loadAt(currentAddr, int64(1<<img.sb.BlkSizeBits)) | ||
| if err != nil { | ||
| img.prefixesErr = fmt.Errorf("failed to load long xattr prefix data at index %d: %w", i, err) | ||
| return | ||
| } | ||
| buf = blk.bytes() | ||
| bufOffset = 0 | ||
| } | ||
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| // Read length (little endian uint16) - includes base_index byte + infix bytes | ||
| prefixLen := int(binary.LittleEndian.Uint16(buf[bufOffset : bufOffset+2])) | ||
| bufOffset += 2 | ||
| currentAddr += 2 | ||
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| if prefixLen < 1 { | ||
| if blk != nil { | ||
| img.putBlock(blk) | ||
| } | ||
| img.prefixesErr = fmt.Errorf("invalid long xattr prefix length %d at index %d", prefixLen, i) | ||
| return | ||
| } | ||
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| // Check if we have enough data for the prefix in current buffer | ||
| if bufOffset+prefixLen > len(buf) { | ||
| // Need to read more data - reload from current position | ||
| if blk != nil { | ||
| img.putBlock(blk) | ||
| } | ||
| // Load enough to cover this prefix | ||
| loadSize := int64(prefixLen) | ||
| if loadSize < int64(1<<img.sb.BlkSizeBits) { | ||
| loadSize = int64(1 << img.sb.BlkSizeBits) | ||
| } | ||
| blk, err = img.loadAt(currentAddr, loadSize) | ||
| if err != nil { | ||
| img.prefixesErr = fmt.Errorf("failed to load long xattr prefix data for index %d: %w", i, err) | ||
| return | ||
| } | ||
| buf = blk.bytes() | ||
| bufOffset = 0 | ||
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| // Verify we have enough now | ||
| if prefixLen > len(buf) { | ||
| img.putBlock(blk) | ||
| img.prefixesErr = fmt.Errorf("long xattr prefix at index %d too large (%d bytes)", i, prefixLen) | ||
| return | ||
| } | ||
| } | ||
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| // First byte is the base_index | ||
| baseIndex := xattrIndex(buf[bufOffset]) | ||
| bufOffset++ | ||
| currentAddr++ | ||
| prefixLen-- | ||
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| // Remaining bytes are the infix | ||
| infix := string(buf[bufOffset : bufOffset+prefixLen]) | ||
| bufOffset += prefixLen | ||
| currentAddr += int64(prefixLen) | ||
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| // Construct full prefix: base prefix + infix | ||
| img.longPrefixes[i] = baseIndex.String() + infix | ||
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| // Align to 4-byte boundary | ||
| // Total length field (2 bytes) + data (base_index + infix) | ||
| totalLen := 2 + 1 + prefixLen | ||
| if rem := totalLen % 4; rem != 0 { | ||
| padding := 4 - rem | ||
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There was a problem hiding this comment. The magic numbers 2, 1, and 4 in the alignment calculation should be defined as named constants (e.g., |
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| bufOffset += padding | ||
| currentAddr += int64(padding) | ||
| } | ||
| } | ||
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| if blk != nil { | ||
| img.putBlock(blk) | ||
| } | ||
| }) | ||
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| return img.prefixesErr | ||
| } | ||
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| // getLongPrefix returns the long xattr prefix at the given index | ||
| func (img *image) getLongPrefix(index uint8) (string, error) { | ||
| if err := img.loadLongPrefixes(); err != nil { | ||
| return "", err | ||
| } | ||
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| if int(index) >= len(img.longPrefixes) { | ||
| return "", fmt.Errorf("long xattr prefix index %d out of range (max %d)", index, len(img.longPrefixes)-1) | ||
| } | ||
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| return img.longPrefixes[index], nil | ||
| } | ||
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| func (img *image) loadAt(addr, size int64) (*block, error) { | ||
| blkSize := int64(1 << img.sb.BlkSizeBits) | ||
| if size > blkSize { | ||
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Hi Derek @dmcgowan, long xattr prefixes (Linux 6.4~6.16)were defined as:
However this way is flew because:
So long xattr prefixes placement is fixed as: https://git.kernel.org/xiang/erofs-utils/c/0cf1039782b2
I admit it was messy initially due to lack of more deeply thoughts when this feature was firstly landed, but it's now fixed.
the implementation can be refered: https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/tree/lib/xattr.c?id=0cf1039782b2#n1680
and
https://git.kernel.org/torvalds/c/1fcf686def19