Documentation/filesystems/ext4/bitmaps.rst
Source file repositories/reference/linux-study-clean/Documentation/filesystems/ext4/bitmaps.rst
File Facts
- System
- Linux kernel
- Corpus path
Documentation/filesystems/ext4/bitmaps.rst- Extension
.rst- Size
- 871 bytes
- Lines
- 22
- Domain
- Support Tooling And Documentation
- Bucket
- Documentation
- Inferred role
- Support Tooling And Documentation: documentation
- Status
- atlas-only
Why This File Exists
Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
- Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
Dependency Surface
- No C-style include directives detected by the generator.
Detected Declarations
- No top-level syscall, struct, function, initcall, or export declaration detected by the generator.
Annotated Snippet
.. 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.Annotation
- Atlas domain: Support Tooling And Documentation / Documentation.
- Implementation status: atlas-only.
Implementation Notes
- This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
- Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
- Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.