From: Darrick J. Wong Date: Sun, 29 Jul 2018 19:37:00 +0000 (-0400) Subject: ext4: import on-disk layout book from wiki page X-Git-Tag: v5.15~7991^2~43 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=b2e60723c1c14c7c9b79c82bb86d8e2a81051b5e;p=platform%2Fkernel%2Flinux-starfive.git ext4: import on-disk layout book from wiki page Create the basic structure of the "new" data structures & algorithms book to be ported over from the on-disk format wiki, and then start by pulling in the introductory information. Signed-off-by: Darrick J. Wong Signed-off-by: Theodore Ts'o --- diff --git a/Documentation/filesystems/ext4/index.rst b/Documentation/filesystems/ext4/index.rst index 1270b34..8fe4f76 100644 --- a/Documentation/filesystems/ext4/index.rst +++ b/Documentation/filesystems/ext4/index.rst @@ -14,3 +14,4 @@ the ext4 community. :numbered: ext4 + ondisk/index diff --git a/Documentation/filesystems/ext4/ondisk/about.rst b/Documentation/filesystems/ext4/ondisk/about.rst new file mode 100644 index 0000000..0aadba0 --- /dev/null +++ b/Documentation/filesystems/ext4/ondisk/about.rst @@ -0,0 +1,44 @@ +.. SPDX-License-Identifier: GPL-2.0 + +About this Book +=============== + +This document attempts to describe the on-disk format for ext4 +filesystems. The same general ideas should apply to ext2/3 filesystems +as well, though they do not support all the features that ext4 supports, +and the fields will be shorter. + +**NOTE**: This is a work in progress, based on notes that the author +(djwong) made while picking apart a filesystem by hand. The data +structure definitions should be current as of Linux 4.18 and +e2fsprogs-1.44. All comments and corrections are welcome, since there is +undoubtedly plenty of lore that might not be reflected in freshly +created demonstration filesystems. + +License +------- +This book is licensed under the terms of the GNU Public License, v2. + +Terminology +----------- + +ext4 divides a storage device into an array of logical blocks both to +reduce bookkeeping overhead and to increase throughput by forcing larger +transfer sizes. Generally, the block size will be 4KiB (the same size as +pages on x86 and the block layer's default block size), though the +actual size is calculated as 2 ^ (10 + ``sb.s_log_block_size``) bytes. +Throughout this document, disk locations are given in terms of these +logical blocks, not raw LBAs, and not 1024-byte blocks. For the sake of +convenience, the logical block size will be referred to as +``$block_size`` throughout the rest of the document. + +When referenced in ``preformatted text`` blocks, ``sb`` refers to fields +in the super block, and ``inode`` refers to fields in an inode table +entry. + +Other References +---------------- + +Also see http://www.nongnu.org/ext2-doc/ for quite a collection of +information about ext2/3. Here's another old reference: +http://wiki.osdev.org/Ext2 diff --git a/Documentation/filesystems/ext4/ondisk/index.rst b/Documentation/filesystems/ext4/ondisk/index.rst new file mode 100644 index 0000000..98cde12 --- /dev/null +++ b/Documentation/filesystems/ext4/ondisk/index.rst @@ -0,0 +1,6 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================== +Data Structures and Algorithms +============================== +.. include:: about.rst