1*4882a593Smuzhiyun.. SPDX-License-Identifier: GPL-2.0 2*4882a593Smuzhiyun 3*4882a593SmuzhiyunInline Data 4*4882a593Smuzhiyun----------- 5*4882a593Smuzhiyun 6*4882a593SmuzhiyunThe inline data feature was designed to handle the case that a file's 7*4882a593Smuzhiyundata is so tiny that it readily fits inside the inode, which 8*4882a593Smuzhiyun(theoretically) reduces disk block consumption and reduces seeks. If the 9*4882a593Smuzhiyunfile is smaller than 60 bytes, then the data are stored inline in 10*4882a593Smuzhiyun``inode.i_block``. If the rest of the file would fit inside the extended 11*4882a593Smuzhiyunattribute space, then it might be found as an extended attribute 12*4882a593Smuzhiyun“system.data” within the inode body (“ibody EA”). This of course 13*4882a593Smuzhiyunconstrains the amount of extended attributes one can attach to an inode. 14*4882a593SmuzhiyunIf the data size increases beyond i\_block + ibody EA, a regular block 15*4882a593Smuzhiyunis allocated and the contents moved to that block. 16*4882a593Smuzhiyun 17*4882a593SmuzhiyunPending a change to compact the extended attribute key used to store 18*4882a593Smuzhiyuninline data, one ought to be able to store 160 bytes of data in a 19*4882a593Smuzhiyun256-byte inode (as of June 2015, when i\_extra\_isize is 28). Prior to 20*4882a593Smuzhiyunthat, the limit was 156 bytes due to inefficient use of inode space. 21*4882a593Smuzhiyun 22*4882a593SmuzhiyunThe inline data feature requires the presence of an extended attribute 23*4882a593Smuzhiyunfor “system.data”, even if the attribute value is zero length. 24*4882a593Smuzhiyun 25*4882a593SmuzhiyunInline Directories 26*4882a593Smuzhiyun~~~~~~~~~~~~~~~~~~ 27*4882a593Smuzhiyun 28*4882a593SmuzhiyunThe first four bytes of i\_block are the inode number of the parent 29*4882a593Smuzhiyundirectory. Following that is a 56-byte space for an array of directory 30*4882a593Smuzhiyunentries; see ``struct ext4_dir_entry``. If there is a “system.data” 31*4882a593Smuzhiyunattribute in the inode body, the EA value is an array of 32*4882a593Smuzhiyun``struct ext4_dir_entry`` as well. Note that for inline directories, the 33*4882a593Smuzhiyuni\_block and EA space are treated as separate dirent blocks; directory 34*4882a593Smuzhiyunentries cannot span the two. 35*4882a593Smuzhiyun 36*4882a593SmuzhiyunInline directory entries are not checksummed, as the inode checksum 37*4882a593Smuzhiyunshould protect all inline data contents. 38