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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/filesystems/ext4/inlinedata.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/filesystems/ext4/inlinedata.rst | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4/inlinedata.rst b/Documentation/filesystems/ext4/inlinedata.rst new file mode 100644 index 000000000..d1075178c --- /dev/null +++ b/Documentation/filesystems/ext4/inlinedata.rst @@ -0,0 +1,37 @@ +.. 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. |