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diff --git a/Documentation/filesystems/ext4/ondisk/group_descr.rst b/Documentation/filesystems/ext4/ondisk/group_descr.rst deleted file mode 100644 index 759827e5d2cf9..0000000000000 --- a/Documentation/filesystems/ext4/ondisk/group_descr.rst +++ /dev/null @@ -1,170 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -Block Group Descriptors ------------------------ - -Each block group on the filesystem has one of these descriptors -associated with it. As noted in the Layout section above, the group -descriptors (if present) are the second item in the block group. The -standard configuration is for each block group to contain a full copy of -the block group descriptor table unless the sparse\_super feature flag -is set. - -Notice how the group descriptor records the location of both bitmaps and -the inode table (i.e. they can float). This means that within a block -group, the only data structures with fixed locations are the superblock -and the group descriptor table. The flex\_bg mechanism uses this -property to group several block groups into a flex group and lay out all -of the groups' bitmaps and inode tables into one long run in the first -group of the flex group. - -If the meta\_bg feature flag is set, then several block groups are -grouped together into a meta group. Note that in the meta\_bg case, -however, the first and last two block groups within the larger meta -group contain only group descriptors for the groups inside the meta -group. - -flex\_bg and meta\_bg do not appear to be mutually exclusive features. - -In ext2, ext3, and ext4 (when the 64bit feature is not enabled), the -block group descriptor was only 32 bytes long and therefore ends at -bg\_checksum. On an ext4 filesystem with the 64bit feature enabled, the -block group descriptor expands to at least the 64 bytes described below; -the size is stored in the superblock. - -If gdt\_csum is set and metadata\_csum is not set, the block group -checksum is the crc16 of the FS UUID, the group number, and the group -descriptor structure. If metadata\_csum is set, then the block group -checksum is the lower 16 bits of the checksum of the FS UUID, the group -number, and the group descriptor structure. Both block and inode bitmap -checksums are calculated against the FS UUID, the group number, and the -entire bitmap. - -The block group descriptor is laid out in ``struct ext4_group_desc``. - -.. list-table:: - :widths: 1 1 1 77 - :header-rows: 1 - - * - Offset - - Size - - Name - - Description - * - 0x0 - - \_\_le32 - - bg\_block\_bitmap\_lo - - Lower 32-bits of location of block bitmap. - * - 0x4 - - \_\_le32 - - bg\_inode\_bitmap\_lo - - Lower 32-bits of location of inode bitmap. - * - 0x8 - - \_\_le32 - - bg\_inode\_table\_lo - - Lower 32-bits of location of inode table. - * - 0xC - - \_\_le16 - - bg\_free\_blocks\_count\_lo - - Lower 16-bits of free block count. - * - 0xE - - \_\_le16 - - bg\_free\_inodes\_count\_lo - - Lower 16-bits of free inode count. - * - 0x10 - - \_\_le16 - - bg\_used\_dirs\_count\_lo - - Lower 16-bits of directory count. - * - 0x12 - - \_\_le16 - - bg\_flags - - Block group flags. See the bgflags_ table below. - * - 0x14 - - \_\_le32 - - bg\_exclude\_bitmap\_lo - - Lower 32-bits of location of snapshot exclusion bitmap. - * - 0x18 - - \_\_le16 - - bg\_block\_bitmap\_csum\_lo - - Lower 16-bits of the block bitmap checksum. - * - 0x1A - - \_\_le16 - - bg\_inode\_bitmap\_csum\_lo - - Lower 16-bits of the inode bitmap checksum. - * - 0x1C - - \_\_le16 - - bg\_itable\_unused\_lo - - Lower 16-bits of unused inode count. If set, we needn't scan past the - ``(sb.s_inodes_per_group - gdt.bg_itable_unused)``\ th entry in the - inode table for this group. - * - 0x1E - - \_\_le16 - - bg\_checksum - - Group descriptor checksum; crc16(sb\_uuid+group+desc) if the - RO\_COMPAT\_GDT\_CSUM feature is set, or crc32c(sb\_uuid+group\_desc) & - 0xFFFF if the RO\_COMPAT\_METADATA\_CSUM feature is set. - * - - - - - - - These fields only exist if the 64bit feature is enabled and s_desc_size - > 32. - * - 0x20 - - \_\_le32 - - bg\_block\_bitmap\_hi - - Upper 32-bits of location of block bitmap. - * - 0x24 - - \_\_le32 - - bg\_inode\_bitmap\_hi - - Upper 32-bits of location of inodes bitmap. - * - 0x28 - - \_\_le32 - - bg\_inode\_table\_hi - - Upper 32-bits of location of inodes table. - * - 0x2C - - \_\_le16 - - bg\_free\_blocks\_count\_hi - - Upper 16-bits of free block count. - * - 0x2E - - \_\_le16 - - bg\_free\_inodes\_count\_hi - - Upper 16-bits of free inode count. - * - 0x30 - - \_\_le16 - - bg\_used\_dirs\_count\_hi - - Upper 16-bits of directory count. - * - 0x32 - - \_\_le16 - - bg\_itable\_unused\_hi - - Upper 16-bits of unused inode count. - * - 0x34 - - \_\_le32 - - bg\_exclude\_bitmap\_hi - - Upper 32-bits of location of snapshot exclusion bitmap. - * - 0x38 - - \_\_le16 - - bg\_block\_bitmap\_csum\_hi - - Upper 16-bits of the block bitmap checksum. - * - 0x3A - - \_\_le16 - - bg\_inode\_bitmap\_csum\_hi - - Upper 16-bits of the inode bitmap checksum. - * - 0x3C - - \_\_u32 - - bg\_reserved - - Padding to 64 bytes. - -.. _bgflags: - -Block group flags can be any combination of the following: - -.. list-table:: - :widths: 1 79 - :header-rows: 1 - - * - Value - - Description - * - 0x1 - - inode table and bitmap are not initialized (EXT4\_BG\_INODE\_UNINIT). - * - 0x2 - - block bitmap is not initialized (EXT4\_BG\_BLOCK\_UNINIT). - * - 0x4 - - inode table is zeroed (EXT4\_BG\_INODE\_ZEROED). |