mirror of https://github.com/Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
37 lines
1.7 KiB
37 lines
1.7 KiB
.. SPDX-License-Identifier: GPL-2.0 |
|
|
|
Inline Data |
|
----------- |
|
|
|
The inline data feature was designed to handle the case that a file's |
|
data is so tiny that it readily fits inside the inode, which |
|
(theoretically) reduces disk block consumption and reduces seeks. If the |
|
file is smaller than 60 bytes, then the data are stored inline in |
|
``inode.i_block``. If the rest of the file would fit inside the extended |
|
attribute space, then it might be found as an extended attribute |
|
“system.data” within the inode body (“ibody EA”). This of course |
|
constrains the amount of extended attributes one can attach to an inode. |
|
If the data size increases beyond i\_block + ibody EA, a regular block |
|
is allocated and the contents moved to that block. |
|
|
|
Pending a change to compact the extended attribute key used to store |
|
inline data, one ought to be able to store 160 bytes of data in a |
|
256-byte inode (as of June 2015, when i\_extra\_isize is 28). Prior to |
|
that, the limit was 156 bytes due to inefficient use of inode space. |
|
|
|
The inline data feature requires the presence of an extended attribute |
|
for “system.data”, even if the attribute value is zero length. |
|
|
|
Inline Directories |
|
~~~~~~~~~~~~~~~~~~ |
|
|
|
The first four bytes of i\_block are the inode number of the parent |
|
directory. Following that is a 56-byte space for an array of directory |
|
entries; see ``struct ext4_dir_entry``. If there is a “system.data” |
|
attribute in the inode body, the EA value is an array of |
|
``struct ext4_dir_entry`` as well. Note that for inline directories, the |
|
i\_block and EA space are treated as separate dirent blocks; directory |
|
entries cannot span the two. |
|
|
|
Inline directory entries are not checksummed, as the inode checksum |
|
should protect all inline data contents.
|
|
|