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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2018-08-13 22:34:47 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-08-13 22:34:47 -0700 |
| commit | 10f3e23f07cb0c20f9bcb77a5b5a7eb2a1b2a2fe (patch) | |
| tree | 1fcb34309b3542512c6f3345f092f7adb8c3312c /Documentation/filesystems/ext4/ondisk/bitmaps.rst | |
| parent | 3bb37da509e576c80180fa0e4d1cfcaddf0cb82e (diff) | |
| parent | 863c37fcb14f8b66ea831b45fb35a53ac4a8d69e (diff) | |
| download | linux-10f3e23f07cb0c20f9bcb77a5b5a7eb2a1b2a2fe.tar.bz2 | |
Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
Pull ext4 updates from Ted Ts'o:
- Convert content from the ext4 wiki to Documentation rst files so it
is more likely to be updated as we add new features to ext4.
- Add 64-bit timestamp support to ext4's superblock fields.
- ... and the usual bug fixes and cleanups, including a Spectre gadget
fixup and some hardening against maliciously corrupted file systems.
* tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (34 commits)
ext4: remove unneeded variable "err" in ext4_mb_release_inode_pa()
ext4: improve code readability in ext4_iget()
ext4: fix spectre gadget in ext4_mb_regular_allocator()
ext4: check for NUL characters in extended attribute's name
ext4: use ext4_warning() for sb_getblk failure
ext4: fix race when setting the bitmap corrupted flag
ext4: reset error code in ext4_find_entry in fallback
ext4: handle layout changes to pinned DAX mappings
dax: dax_layout_busy_page() warn on !exceptional
docs: fix up the obviously obsolete bits in the new ext4 documentation
docs: add new ext4 superblock time extension fields
docs: create filesystem internal section
ext4: use swap macro in mext_page_double_lock
ext4: check allocation failure when duplicating "data" in ext4_remount()
ext4: fix warning message in ext4_enable_quotas()
ext4: super: extend timestamps to 40 bits
jbd2: replace current_kernel_time64 with ktime equivalent
ext4: use timespec64 for all inode times
ext4: use ktime_get_real_seconds for i_dtime
ext4: use 64-bit timestamps for mmp_time
...
Diffstat (limited to 'Documentation/filesystems/ext4/ondisk/bitmaps.rst')
| -rw-r--r-- | Documentation/filesystems/ext4/ondisk/bitmaps.rst | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4/ondisk/bitmaps.rst b/Documentation/filesystems/ext4/ondisk/bitmaps.rst new file mode 100644 index 000000000000..c7546dbc197a --- /dev/null +++ b/Documentation/filesystems/ext4/ondisk/bitmaps.rst @@ -0,0 +1,28 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Block and inode Bitmaps +----------------------- + +The data block bitmap tracks the usage of data blocks within the block +group. + +The inode bitmap records which entries in the inode table are in use. + +As with most bitmaps, one bit represents the usage status of one data +block or inode table entry. This implies a block group size of 8 \* +number\_of\_bytes\_in\_a\_logical\_block. + +NOTE: If ``BLOCK_UNINIT`` is set for a given block group, various parts +of the kernel and e2fsprogs code pretends that the block bitmap contains +zeros (i.e. all blocks in the group are free). However, it is not +necessarily the case that no blocks are in use -- if ``meta_bg`` is set, +the bitmaps and group descriptor live inside the group. Unfortunately, +ext2fs\_test\_block\_bitmap2() will return '0' for those locations, +which produces confusing debugfs output. + +Inode Table +----------- +Inode tables are statically allocated at mkfs time. Each block group +descriptor points to the start of the table, and the superblock records +the number of inodes per group. See the section on inodes for more +information. |