filesystems/ext4/directory.rst

6 In an ext4 filesystem, a directory is more or less a flat file that maps
12 associated with a directory file for the particular directory entry that
19 array. I write “almost” because it's not a linear array in the memory
21 Therefore, it is more accurate to say that a directory is a series of
22 data blocks and that each block contains a linear array of directory
24 end of the block; the last entry in the block has a record length that
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51      - Length of this directory entry. Must be a multiple of 4.
62 entry format shortens the name_len field and uses the space for a file
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128 after ``name`` and is included in the size listed by ``rec_len`` If a directory
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149 In order to add checksums to these classic directory blocks, a phony
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194 A linear array of directory entries isn't great for performance, so a
195 new feature was added to ext3 to provide a faster (but peculiar)
196 balanced tree keyed off a hash of the directory entry name. If the
197 EXT4_INDEX_FL (0x1000) flag is set in the inode, this directory uses a
210 the root node contains metadata about the tree and finally a hash->block
214 node, which is indexed by a minor hash. Interior nodes in this tree
215 contains a zeroed out ``struct ext4_dir_entry_2`` followed by a
216 minor_hash->block map to find leafe nodes. Leaf nodes contain a linear
223 To traverse the directory as a htree, the code calculates the hash of
225 number. If the tree is flat, the block is a linear array of directory
228 third block number. That third block number will be a linear array of
231 To traverse the directory as a linear array (such as the old code does),
237 of a data block:
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326      - As many 8-byte ``struct dx_entry`` as fits in the rest of the data block.
354 also the full length of a data block:
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398      - As many 8-byte ``struct dx_entry`` as fits in the rest of the data block.
401 ``struct dx_node`` are recorded as ``struct dx_entry``, which is 8 bytes
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425 If metadata checksums are enabled, the last 8 bytes of the directory
426 block (precisely the length of one dx_entry) are used to store a
432 The dx_tail structure is 8 bytes long and looks like this:
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