filesystems/ext4/group_descr.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 -----------------------
38 checksum is the lower 16 bits of the checksum of the FS UUID, the group
45 .. list-table::
47    :header-rows: 1
49    * - Offset
50      - Size
51      - Name
52      - Description
53    * - 0x0
54      - __le32
55      - bg_block_bitmap_lo
56      - Lower 32-bits of location of block bitmap.
57    * - 0x4
58      - __le32
59      - bg_inode_bitmap_lo
60      - Lower 32-bits of location of inode bitmap.
61    * - 0x8
62      - __le32
63      - bg_inode_table_lo
64      - Lower 32-bits of location of inode table.
65    * - 0xC
66      - __le16
67      - bg_free_blocks_count_lo
68      - Lower 16-bits of free block count.
69    * - 0xE
70      - __le16
71      - bg_free_inodes_count_lo
72      - Lower 16-bits of free inode count.
73    * - 0x10
74      - __le16
75      - bg_used_dirs_count_lo
76      - Lower 16-bits of directory count.
77    * - 0x12
78      - __le16
79      - bg_flags
80      - Block group flags. See the bgflags_ table below.
81    * - 0x14
82      - __le32
83      - bg_exclude_bitmap_lo
84      - Lower 32-bits of location of snapshot exclusion bitmap.
85    * - 0x18
86      - __le16
87      - bg_block_bitmap_csum_lo
88      - Lower 16-bits of the block bitmap checksum.
89    * - 0x1A
90      - __le16
91      - bg_inode_bitmap_csum_lo
92      - Lower 16-bits of the inode bitmap checksum.
93    * - 0x1C
94      - __le16
95      - bg_itable_unused_lo
96      - Lower 16-bits of unused inode count. If set, we needn't scan past the
97        ``(sb.s_inodes_per_group - gdt.bg_itable_unused)`` th entry in the
99    * - 0x1E
100      - __le16
101      - bg_checksum
102      - Group descriptor checksum; crc16(sb_uuid+group_num+bg_desc) if the
108    * -
109      -
110      -
111      - These fields only exist if the 64bit feature is enabled and s_desc_size
113    * - 0x20
114      - __le32
115      - bg_block_bitmap_hi
116      - Upper 32-bits of location of block bitmap.
117    * - 0x24
118      - __le32
119      - bg_inode_bitmap_hi
120      - Upper 32-bits of location of inodes bitmap.
121    * - 0x28
122      - __le32
123      - bg_inode_table_hi
124      - Upper 32-bits of location of inodes table.
125    * - 0x2C
126      - __le16
127      - bg_free_blocks_count_hi
128      - Upper 16-bits of free block count.
129    * - 0x2E
130      - __le16
131      - bg_free_inodes_count_hi
132      - Upper 16-bits of free inode count.
133    * - 0x30
134      - __le16
135      - bg_used_dirs_count_hi
136      - Upper 16-bits of directory count.
137    * - 0x32
138      - __le16
139      - bg_itable_unused_hi
140      - Upper 16-bits of unused inode count.
141    * - 0x34
142      - __le32
143      - bg_exclude_bitmap_hi
144      - Upper 32-bits of location of snapshot exclusion bitmap.
145    * - 0x38
146      - __le16
147      - bg_block_bitmap_csum_hi
148      - Upper 16-bits of the block bitmap checksum.
149    * - 0x3A
150      - __le16
151      - bg_inode_bitmap_csum_hi
152      - Upper 16-bits of the inode bitmap checksum.
153    * - 0x3C
154      - __u32
155      - bg_reserved
156      - Padding to 64 bytes.
162 .. list-table::
163    :widths: 16 64
164    :header-rows: 1
166    * - Value
167      - Description
168    * - 0x1
169      - inode table and bitmap are not initialized (EXT4_BG_INODE_UNINIT).
170    * - 0x2
171      - block bitmap is not initialized (EXT4_BG_BLOCK_UNINIT).
172    * - 0x4
173      - inode table is zeroed (EXT4_BG_INODE_ZEROED).