filesystems/ext4/group_descr.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 -----------------------
30 block group descriptor was only 32 bytes long and therefore ends at
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
112        > 32.
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::
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).