162306a36Sopenharmony_ci.. SPDX-License-Identifier: GPL-2.0 262306a36Sopenharmony_ci 362306a36Sopenharmony_ciInline Data 462306a36Sopenharmony_ci----------- 562306a36Sopenharmony_ci 662306a36Sopenharmony_ciThe inline data feature was designed to handle the case that a file's 762306a36Sopenharmony_cidata is so tiny that it readily fits inside the inode, which 862306a36Sopenharmony_ci(theoretically) reduces disk block consumption and reduces seeks. If the 962306a36Sopenharmony_cifile is smaller than 60 bytes, then the data are stored inline in 1062306a36Sopenharmony_ci``inode.i_block``. If the rest of the file would fit inside the extended 1162306a36Sopenharmony_ciattribute space, then it might be found as an extended attribute 1262306a36Sopenharmony_ci“system.data” within the inode body (“ibody EA”). This of course 1362306a36Sopenharmony_ciconstrains the amount of extended attributes one can attach to an inode. 1462306a36Sopenharmony_ciIf the data size increases beyond i_block + ibody EA, a regular block 1562306a36Sopenharmony_ciis allocated and the contents moved to that block. 1662306a36Sopenharmony_ci 1762306a36Sopenharmony_ciPending a change to compact the extended attribute key used to store 1862306a36Sopenharmony_ciinline data, one ought to be able to store 160 bytes of data in a 1962306a36Sopenharmony_ci256-byte inode (as of June 2015, when i_extra_isize is 28). Prior to 2062306a36Sopenharmony_cithat, the limit was 156 bytes due to inefficient use of inode space. 2162306a36Sopenharmony_ci 2262306a36Sopenharmony_ciThe inline data feature requires the presence of an extended attribute 2362306a36Sopenharmony_cifor “system.data”, even if the attribute value is zero length. 2462306a36Sopenharmony_ci 2562306a36Sopenharmony_ciInline Directories 2662306a36Sopenharmony_ci~~~~~~~~~~~~~~~~~~ 2762306a36Sopenharmony_ci 2862306a36Sopenharmony_ciThe first four bytes of i_block are the inode number of the parent 2962306a36Sopenharmony_cidirectory. Following that is a 56-byte space for an array of directory 3062306a36Sopenharmony_cientries; see ``struct ext4_dir_entry``. If there is a “system.data” 3162306a36Sopenharmony_ciattribute in the inode body, the EA value is an array of 3262306a36Sopenharmony_ci``struct ext4_dir_entry`` as well. Note that for inline directories, the 3362306a36Sopenharmony_cii_block and EA space are treated as separate dirent blocks; directory 3462306a36Sopenharmony_cientries cannot span the two. 3562306a36Sopenharmony_ci 3662306a36Sopenharmony_ciInline directory entries are not checksummed, as the inode checksum 3762306a36Sopenharmony_cishould protect all inline data contents. 38