Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 831 insertions, 0 deletions

diff --git a/Documentation/filesystems/ext4/super.rst b/Documentation/filesystems/ext4/super.rst
new file mode 100644
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+++ b/Documentation/filesystems/ext4/super.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+Super Block
+-----------
+
+The superblock records various information about the enclosing
+filesystem, such as block counts, inode counts, supported features,
+maintenance information, and more.
+
+If the sparse_super feature flag is set, redundant copies of the
+superblock and group descriptors are kept only in the groups whose group
+number is either 0 or a power of 3, 5, or 7. If the flag is not set,
+redundant copies are kept in all groups.
+
+The superblock checksum is calculated against the superblock structure,
+which includes the FS UUID.
+
+The ext4 superblock is laid out as follows in
+``struct ext4_super_block``:
+
+.. list-table::
+   :widths: 8 8 24 40
+   :header-rows: 1
+
+   * - Offset
+     - Size
+     - Name
+     - Description
+   * - 0x0
+     - __le32
+     - s_inodes_count
+     - Total inode count.
+   * - 0x4
+     - __le32
+     - s_blocks_count_lo
+     - Total block count.
+   * - 0x8
+     - __le32
+     - s_r_blocks_count_lo
+     - This number of blocks can only be allocated by the super-user.
+   * - 0xC
+     - __le32
+     - s_free_blocks_count_lo
+     - Free block count.
+   * - 0x10
+     - __le32
+     - s_free_inodes_count
+     - Free inode count.
+   * - 0x14
+     - __le32
+     - s_first_data_block
+     - First data block. This must be at least 1 for 1k-block filesystems and
+       is typically 0 for all other block sizes.
+   * - 0x18
+     - __le32
+     - s_log_block_size
+     - Block size is 2 ^ (10 + s_log_block_size).
+   * - 0x1C
+     - __le32
+     - s_log_cluster_size
+     - Cluster size is 2 ^ (10 + s_log_cluster_size) blocks if bigalloc is
+       enabled. Otherwise s_log_cluster_size must equal s_log_block_size.
+   * - 0x20
+     - __le32
+     - s_blocks_per_group
+     - Blocks per group.
+   * - 0x24
+     - __le32
+     - s_clusters_per_group
+     - Clusters per group, if bigalloc is enabled. Otherwise
+       s_clusters_per_group must equal s_blocks_per_group.
+   * - 0x28
+     - __le32
+     - s_inodes_per_group
+     - Inodes per group.
+   * - 0x2C
+     - __le32
+     - s_mtime
+     - Mount time, in seconds since the epoch.
+   * - 0x30
+     - __le32
+     - s_wtime
+     - Write time, in seconds since the epoch.
+   * - 0x34
+     - __le16
+     - s_mnt_count
+     - Number of mounts since the last fsck.
+   * - 0x36
+     - __le16
+     - s_max_mnt_count
+     - Number of mounts beyond which a fsck is needed.
+   * - 0x38
+     - __le16
+     - s_magic
+     - Magic signature, 0xEF53
+   * - 0x3A
+     - __le16
+     - s_state
+     - File system state. See super_state_ for more info.
+   * - 0x3C
+     - __le16
+     - s_errors
+     - Behaviour when detecting errors. See super_errors_ for more info.
+   * - 0x3E
+     - __le16
+     - s_minor_rev_level
+     - Minor revision level.
+   * - 0x40
+     - __le32
+     - s_lastcheck
+     - Time of last check, in seconds since the epoch.
+   * - 0x44
+     - __le32
+     - s_checkinterval
+     - Maximum time between checks, in seconds.
+   * - 0x48
+     - __le32
+     - s_creator_os
+     - Creator OS. See the table super_creator_ for more info.
+   * - 0x4C
+     - __le32
+     - s_rev_level
+     - Revision level. See the table super_revision_ for more info.
+   * - 0x50
+     - __le16
+     - s_def_resuid
+     - Default uid for reserved blocks.
+   * - 0x52
+     - __le16
+     - s_def_resgid
+     - Default gid for reserved blocks.
+   * -
+     -
+     -
+     - These fields are for EXT4_DYNAMIC_REV superblocks only.
+       
+       Note: the difference between the compatible feature set and the
+       incompatible feature set is that if there is a bit set in the
+       incompatible feature set that the kernel doesn't know about, it should
+       refuse to mount the filesystem.
+       
+       e2fsck's requirements are more strict; if it doesn't know
+       about a feature in either the compatible or incompatible feature set, it
+       must abort and not try to meddle with things it doesn't understand...
+   * - 0x54
+     - __le32
+     - s_first_ino
+     - First non-reserved inode.
+   * - 0x58
+     - __le16
+     - s_inode_size
+     - Size of inode structure, in bytes.
+   * - 0x5A
+     - __le16
+     - s_block_group_nr
+     - Block group # of this superblock.
+   * - 0x5C
+     - __le32
+     - s_feature_compat
+     - Compatible feature set flags. Kernel can still read/write this fs even
+       if it doesn't understand a flag; fsck should not do that. See the
+       super_compat_ table for more info.
+   * - 0x60
+     - __le32
+     - s_feature_incompat
+     - Incompatible feature set. If the kernel or fsck doesn't understand one
+       of these bits, it should stop. See the super_incompat_ table for more
+       info.
+   * - 0x64
+     - __le32
+     - s_feature_ro_compat
+     - Readonly-compatible feature set. If the kernel doesn't understand one of
+       these bits, it can still mount read-only. See the super_rocompat_ table
+       for more info.
+   * - 0x68
+     - __u8
+     - s_uuid[16]
+     - 128-bit UUID for volume.
+   * - 0x78
+     - char
+     - s_volume_name[16]
+     - Volume label.
+   * - 0x88
+     - char
+     - s_last_mounted[64]
+     - Directory where filesystem was last mounted.
+   * - 0xC8
+     - __le32
+     - s_algorithm_usage_bitmap
+     - For compression (Not used in e2fsprogs/Linux)
+   * -
+     -
+     -
+     - Performance hints.  Directory preallocation should only happen if the
+       EXT4_FEATURE_COMPAT_DIR_PREALLOC flag is on.
+   * - 0xCC
+     - __u8
+     - s_prealloc_blocks
+     - #. of blocks to try to preallocate for ... files? (Not used in
+       e2fsprogs/Linux)
+   * - 0xCD
+     - __u8
+     - s_prealloc_dir_blocks
+     - #. of blocks to preallocate for directories. (Not used in
+       e2fsprogs/Linux)
+   * - 0xCE
+     - __le16
+     - s_reserved_gdt_blocks
+     - Number of reserved GDT entries for future filesystem expansion.
+   * -
+     -
+     -
+     - Journalling support is valid only if EXT4_FEATURE_COMPAT_HAS_JOURNAL is
+       set.
+   * - 0xD0
+     - __u8
+     - s_journal_uuid[16]
+     - UUID of journal superblock
+   * - 0xE0
+     - __le32
+     - s_journal_inum
+     - inode number of journal file.
+   * - 0xE4
+     - __le32
+     - s_journal_dev
+     - Device number of journal file, if the external journal feature flag is
+       set.
+   * - 0xE8
+     - __le32
+     - s_last_orphan
+     - Start of list of orphaned inodes to delete.
+   * - 0xEC
+     - __le32
+     - s_hash_seed[4]
+     - HTREE hash seed.
+   * - 0xFC
+     - __u8
+     - s_def_hash_version
+     - Default hash algorithm to use for directory hashes. See super_def_hash_
+       for more info.
+   * - 0xFD
+     - __u8
+     - s_jnl_backup_type
+     - If this value is 0 or EXT3_JNL_BACKUP_BLOCKS (1), then the
+       ``s_jnl_blocks`` field contains a duplicate copy of the inode's
+       ``i_block[]`` array and ``i_size``.
+   * - 0xFE
+     - __le16
+     - s_desc_size
+     - Size of group descriptors, in bytes, if the 64bit incompat feature flag
+       is set.
+   * - 0x100
+     - __le32
+     - s_default_mount_opts
+     - Default mount options. See the super_mountopts_ table for more info.
+   * - 0x104
+     - __le32
+     - s_first_meta_bg
+     - First metablock block group, if the meta_bg feature is enabled.
+   * - 0x108
+     - __le32
+     - s_mkfs_time
+     - When the filesystem was created, in seconds since the epoch.
+   * - 0x10C
+     - __le32
+     - s_jnl_blocks[17]
+     - Backup copy of the journal inode's ``i_block[]`` array in the first 15
+       elements and i_size_high and i_size in the 16th and 17th elements,
+       respectively.
+   * -
+     -
+     -
+     - 64bit support is valid only if EXT4_FEATURE_COMPAT_64BIT is set.
+   * - 0x150
+     - __le32
+     - s_blocks_count_hi
+     - High 32-bits of the block count.
+   * - 0x154
+     - __le32
+     - s_r_blocks_count_hi
+     - High 32-bits of the reserved block count.
+   * - 0x158
+     - __le32
+     - s_free_blocks_count_hi
+     - High 32-bits of the free block count.
+   * - 0x15C
+     - __le16
+     - s_min_extra_isize
+     - All inodes have at least # bytes.
+   * - 0x15E
+     - __le16
+     - s_want_extra_isize
+     - New inodes should reserve # bytes.
+   * - 0x160
+     - __le32
+     - s_flags
+     - Miscellaneous flags. See the super_flags_ table for more info.
+   * - 0x164
+     - __le16
+     - s_raid_stride
+     - RAID stride. This is the number of logical blocks read from or written
+       to the disk before moving to the next disk. This affects the placement
+       of filesystem metadata, which will hopefully make RAID storage faster.
+   * - 0x166
+     - __le16
+     - s_mmp_interval
+     - #. seconds to wait in multi-mount prevention (MMP) checking. In theory,
+       MMP is a mechanism to record in the superblock which host and device
+       have mounted the filesystem, in order to prevent multiple mounts. This
+       feature does not seem to be implemented...
+   * - 0x168
+     - __le64
+     - s_mmp_block
+     - Block # for multi-mount protection data.
+   * - 0x170
+     - __le32
+     - s_raid_stripe_width
+     - RAID stripe width. This is the number of logical blocks read from or
+       written to the disk before coming back to the current disk. This is used
+       by the block allocator to try to reduce the number of read-modify-write
+       operations in a RAID5/6.
+   * - 0x174
+     - __u8
+     - s_log_groups_per_flex
+     - Size of a flexible block group is 2 ^ ``s_log_groups_per_flex``.
+   * - 0x175
+     - __u8
+     - s_checksum_type
+     - Metadata checksum algorithm type. The only valid value is 1 (crc32c).
+   * - 0x176
+     - __le16
+     - s_reserved_pad
+     -
+   * - 0x178
+     - __le64
+     - s_kbytes_written
+     - Number of KiB written to this filesystem over its lifetime.
+   * - 0x180
+     - __le32
+     - s_snapshot_inum
+     - inode number of active snapshot. (Not used in e2fsprogs/Linux.)
+   * - 0x184
+     - __le32
+     - s_snapshot_id
+     - Sequential ID of active snapshot. (Not used in e2fsprogs/Linux.)
+   * - 0x188
+     - __le64
+     - s_snapshot_r_blocks_count
+     - Number of blocks reserved for active snapshot's future use. (Not used in
+       e2fsprogs/Linux.)
+   * - 0x190
+     - __le32
+     - s_snapshot_list
+     - inode number of the head of the on-disk snapshot list. (Not used in
+       e2fsprogs/Linux.)
+   * - 0x194
+     - __le32
+     - s_error_count
+     - Number of errors seen.
+   * - 0x198
+     - __le32
+     - s_first_error_time
+     - First time an error happened, in seconds since the epoch.
+   * - 0x19C
+     - __le32
+     - s_first_error_ino
+     - inode involved in first error.
+   * - 0x1A0
+     - __le64
+     - s_first_error_block
+     - Number of block involved of first error.
+   * - 0x1A8
+     - __u8
+     - s_first_error_func[32]
+     - Name of function where the error happened.
+   * - 0x1C8
+     - __le32
+     - s_first_error_line
+     - Line number where error happened.
+   * - 0x1CC
+     - __le32
+     - s_last_error_time
+     - Time of most recent error, in seconds since the epoch.
+   * - 0x1D0
+     - __le32
+     - s_last_error_ino
+     - inode involved in most recent error.
+   * - 0x1D4
+     - __le32
+     - s_last_error_line
+     - Line number where most recent error happened.
+   * - 0x1D8
+     - __le64
+     - s_last_error_block
+     - Number of block involved in most recent error.
+   * - 0x1E0
+     - __u8
+     - s_last_error_func[32]
+     - Name of function where the most recent error happened.
+   * - 0x200
+     - __u8
+     - s_mount_opts[64]
+     - ASCIIZ string of mount options.
+   * - 0x240
+     - __le32
+     - s_usr_quota_inum
+     - Inode number of user `quota <quota>`__ file.
+   * - 0x244
+     - __le32
+     - s_grp_quota_inum
+     - Inode number of group `quota <quota>`__ file.
+   * - 0x248
+     - __le32
+     - s_overhead_blocks
+     - Overhead blocks/clusters in fs. (Huh? This field is always zero, which
+       means that the kernel calculates it dynamically.)
+   * - 0x24C
+     - __le32
+     - s_backup_bgs[2]
+     - Block groups containing superblock backups (if sparse_super2)
+   * - 0x254
+     - __u8
+     - s_encrypt_algos[4]
+     - Encryption algorithms in use. There can be up to four algorithms in use
+       at any time; valid algorithm codes are given in the super_encrypt_ table
+       below.
+   * - 0x258
+     - __u8
+     - s_encrypt_pw_salt[16]
+     - Salt for the string2key algorithm for encryption.
+   * - 0x268
+     - __le32
+     - s_lpf_ino
+     - Inode number of lost+found
+   * - 0x26C
+     - __le32
+     - s_prj_quota_inum
+     - Inode that tracks project quotas.
+   * - 0x270
+     - __le32
+     - s_checksum_seed
+     - Checksum seed used for metadata_csum calculations. This value is
+       crc32c(~0, $orig_fs_uuid).
+   * - 0x274
+     - __u8
+     - s_wtime_hi
+     - Upper 8 bits of the s_wtime field.
+   * - 0x275
+     - __u8
+     - s_mtime_hi
+     - Upper 8 bits of the s_mtime field.
+   * - 0x276
+     - __u8
+     - s_mkfs_time_hi
+     - Upper 8 bits of the s_mkfs_time field.
+   * - 0x277
+     - __u8
+     - s_lastcheck_hi
+     - Upper 8 bits of the s_lastcheck field.
+   * - 0x278
+     - __u8
+     - s_first_error_time_hi
+     - Upper 8 bits of the s_first_error_time field.
+   * - 0x279
+     - __u8
+     - s_last_error_time_hi
+     - Upper 8 bits of the s_last_error_time field.
+   * - 0x27A
+     - __u8
+     - s_pad[2]
+     - Zero padding.
+   * - 0x27C
+     - __le16
+     - s_encoding
+     - Filename charset encoding.
+   * - 0x27E
+     - __le16
+     - s_encoding_flags
+     - Filename charset encoding flags.
+   * - 0x280
+     - __le32
+     - s_orphan_file_inum
+     - Orphan file inode number.
+   * - 0x284
+     - __le32
+     - s_reserved[94]
+     - Padding to the end of the block.
+   * - 0x3FC
+     - __le32
+     - s_checksum
+     - Superblock checksum.
+
+.. _super_state:
+
+The superblock state is some combination of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x0001
+     - Cleanly umounted
+   * - 0x0002
+     - Errors detected
+   * - 0x0004
+     - Orphans being recovered
+
+.. _super_errors:
+
+The superblock error policy is one of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 1
+     - Continue
+   * - 2
+     - Remount read-only
+   * - 3
+     - Panic
+
+.. _super_creator:
+
+The filesystem creator is one of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0
+     - Linux
+   * - 1
+     - Hurd
+   * - 2
+     - Masix
+   * - 3
+     - FreeBSD
+   * - 4
+     - Lites
+
+.. _super_revision:
+
+The superblock revision is one of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0
+     - Original format
+   * - 1
+     - v2 format w/ dynamic inode sizes
+
+Note that ``EXT4_DYNAMIC_REV`` refers to a revision 1 or newer filesystem.
+
+.. _super_compat:
+
+The superblock compatible features field is a combination of any of the
+following:
+
+.. list-table::
+   :widths: 16 64
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x1
+     - Directory preallocation (COMPAT_DIR_PREALLOC).
+   * - 0x2
+     - “imagic inodes”. Not clear from the code what this does
+       (COMPAT_IMAGIC_INODES).
+   * - 0x4
+     - Has a journal (COMPAT_HAS_JOURNAL).
+   * - 0x8
+     - Supports extended attributes (COMPAT_EXT_ATTR).
+   * - 0x10
+     - Has reserved GDT blocks for filesystem expansion
+       (COMPAT_RESIZE_INODE). Requires RO_COMPAT_SPARSE_SUPER.
+   * - 0x20
+     - Has directory indices (COMPAT_DIR_INDEX).
+   * - 0x40
+     - “Lazy BG”. Not in Linux kernel, seems to have been for uninitialized
+       block groups? (COMPAT_LAZY_BG)
+   * - 0x80
+     - “Exclude inode”. Not used. (COMPAT_EXCLUDE_INODE).
+   * - 0x100
+     - “Exclude bitmap”. Seems to be used to indicate the presence of
+       snapshot-related exclude bitmaps? Not defined in kernel or used in
+       e2fsprogs (COMPAT_EXCLUDE_BITMAP).
+   * - 0x200
+     - Sparse Super Block, v2. If this flag is set, the SB field s_backup_bgs
+       points to the two block groups that contain backup superblocks
+       (COMPAT_SPARSE_SUPER2).
+   * - 0x400
+     - Fast commits supported. Although fast commits blocks are
+       backward incompatible, fast commit blocks are not always
+       present in the journal. If fast commit blocks are present in
+       the journal, JBD2 incompat feature
+       (JBD2_FEATURE_INCOMPAT_FAST_COMMIT) gets
+       set (COMPAT_FAST_COMMIT).
+   * - 0x1000
+     - Orphan file allocated. This is the special file for more efficient
+       tracking of unlinked but still open inodes. When there may be any
+       entries in the file, we additionally set proper rocompat feature
+       (RO_COMPAT_ORPHAN_PRESENT).
+
+.. _super_incompat:
+
+The superblock incompatible features field is a combination of any of the
+following:
+
+.. list-table::
+   :widths: 16 64
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x1
+     - Compression (INCOMPAT_COMPRESSION).
+   * - 0x2
+     - Directory entries record the file type. See ext4_dir_entry_2 below
+       (INCOMPAT_FILETYPE).
+   * - 0x4
+     - Filesystem needs recovery (INCOMPAT_RECOVER).
+   * - 0x8
+     - Filesystem has a separate journal device (INCOMPAT_JOURNAL_DEV).
+   * - 0x10
+     - Meta block groups. See the earlier discussion of this feature
+       (INCOMPAT_META_BG).
+   * - 0x40
+     - Files in this filesystem use extents (INCOMPAT_EXTENTS).
+   * - 0x80
+     - Enable a filesystem size of 2^64 blocks (INCOMPAT_64BIT).
+   * - 0x100
+     - Multiple mount protection (INCOMPAT_MMP).
+   * - 0x200
+     - Flexible block groups. See the earlier discussion of this feature
+       (INCOMPAT_FLEX_BG).
+   * - 0x400
+     - Inodes can be used to store large extended attribute values
+       (INCOMPAT_EA_INODE).
+   * - 0x1000
+     - Data in directory entry (INCOMPAT_DIRDATA). (Not implemented?)
+   * - 0x2000
+     - Metadata checksum seed is stored in the superblock. This feature enables
+       the administrator to change the UUID of a metadata_csum filesystem
+       while the filesystem is mounted; without it, the checksum definition
+       requires all metadata blocks to be rewritten (INCOMPAT_CSUM_SEED).
+   * - 0x4000
+     - Large directory >2GB or 3-level htree (INCOMPAT_LARGEDIR). Prior to
+       this feature, directories could not be larger than 4GiB and could not
+       have an htree more than 2 levels deep. If this feature is enabled,
+       directories can be larger than 4GiB and have a maximum htree depth of 3.
+   * - 0x8000
+     - Data in inode (INCOMPAT_INLINE_DATA).
+   * - 0x10000
+     - Encrypted inodes are present on the filesystem. (INCOMPAT_ENCRYPT).
+
+.. _super_rocompat:
+
+The superblock read-only compatible features field is a combination of any of
+the following:
+
+.. list-table::
+   :widths: 16 64
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x1
+     - Sparse superblocks. See the earlier discussion of this feature
+       (RO_COMPAT_SPARSE_SUPER).
+   * - 0x2
+     - This filesystem has been used to store a file greater than 2GiB
+       (RO_COMPAT_LARGE_FILE).
+   * - 0x4
+     - Not used in kernel or e2fsprogs (RO_COMPAT_BTREE_DIR).
+   * - 0x8
+     - This filesystem has files whose sizes are represented in units of
+       logical blocks, not 512-byte sectors. This implies a very large file
+       indeed! (RO_COMPAT_HUGE_FILE)
+   * - 0x10
+     - Group descriptors have checksums. In addition to detecting corruption,
+       this is useful for lazy formatting with uninitialized groups
+       (RO_COMPAT_GDT_CSUM).
+   * - 0x20
+     - Indicates that the old ext3 32,000 subdirectory limit no longer applies
+       (RO_COMPAT_DIR_NLINK). A directory's i_links_count will be set to 1
+       if it is incremented past 64,999.
+   * - 0x40
+     - Indicates that large inodes exist on this filesystem
+       (RO_COMPAT_EXTRA_ISIZE).
+   * - 0x80
+     - This filesystem has a snapshot (RO_COMPAT_HAS_SNAPSHOT).
+   * - 0x100
+     - `Quota <Quota>`__ (RO_COMPAT_QUOTA).
+   * - 0x200
+     - This filesystem supports “bigalloc”, which means that file extents are
+       tracked in units of clusters (of blocks) instead of blocks
+       (RO_COMPAT_BIGALLOC).
+   * - 0x400
+     - This filesystem supports metadata checksumming.
+       (RO_COMPAT_METADATA_CSUM; implies RO_COMPAT_GDT_CSUM, though
+       GDT_CSUM must not be set)
+   * - 0x800
+     - Filesystem supports replicas. This feature is neither in the kernel nor
+       e2fsprogs. (RO_COMPAT_REPLICA)
+   * - 0x1000
+     - Read-only filesystem image; the kernel will not mount this image
+       read-write and most tools will refuse to write to the image.
+       (RO_COMPAT_READONLY)
+   * - 0x2000
+     - Filesystem tracks project quotas. (RO_COMPAT_PROJECT)
+   * - 0x8000
+     - Verity inodes may be present on the filesystem. (RO_COMPAT_VERITY)
+   * - 0x10000
+     - Indicates orphan file may have valid orphan entries and thus we need
+       to clean them up when mounting the filesystem
+       (RO_COMPAT_ORPHAN_PRESENT).
+
+.. _super_def_hash:
+
+The ``s_def_hash_version`` field is one of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x0
+     - Legacy.
+   * - 0x1
+     - Half MD4.
+   * - 0x2
+     - Tea.
+   * - 0x3
+     - Legacy, unsigned.
+   * - 0x4
+     - Half MD4, unsigned.
+   * - 0x5
+     - Tea, unsigned.
+
+.. _super_mountopts:
+
+The ``s_default_mount_opts`` field is any combination of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x0001
+     - Print debugging info upon (re)mount. (EXT4_DEFM_DEBUG)
+   * - 0x0002
+     - New files take the gid of the containing directory (instead of the fsgid
+       of the current process). (EXT4_DEFM_BSDGROUPS)
+   * - 0x0004
+     - Support userspace-provided extended attributes. (EXT4_DEFM_XATTR_USER)
+   * - 0x0008
+     - Support POSIX access control lists (ACLs). (EXT4_DEFM_ACL)
+   * - 0x0010
+     - Do not support 32-bit UIDs. (EXT4_DEFM_UID16)
+   * - 0x0020
+     - All data and metadata are commited to the journal.
+       (EXT4_DEFM_JMODE_DATA)
+   * - 0x0040
+     - All data are flushed to the disk before metadata are committed to the
+       journal. (EXT4_DEFM_JMODE_ORDERED)
+   * - 0x0060
+     - Data ordering is not preserved; data may be written after the metadata
+       has been written. (EXT4_DEFM_JMODE_WBACK)
+   * - 0x0100
+     - Disable write flushes. (EXT4_DEFM_NOBARRIER)
+   * - 0x0200
+     - Track which blocks in a filesystem are metadata and therefore should not
+       be used as data blocks. This option will be enabled by default on 3.18,
+       hopefully. (EXT4_DEFM_BLOCK_VALIDITY)
+   * - 0x0400
+     - Enable DISCARD support, where the storage device is told about blocks
+       becoming unused. (EXT4_DEFM_DISCARD)
+   * - 0x0800
+     - Disable delayed allocation. (EXT4_DEFM_NODELALLOC)
+
+.. _super_flags:
+
+The ``s_flags`` field is any combination of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0x0001
+     - Signed directory hash in use.
+   * - 0x0002
+     - Unsigned directory hash in use.
+   * - 0x0004
+     - To test development code.
+
+.. _super_encrypt:
+
+The ``s_encrypt_algos`` list can contain any of the following:
+
+.. list-table::
+   :widths: 8 72
+   :header-rows: 1
+
+   * - Value
+     - Description
+   * - 0
+     - Invalid algorithm (ENCRYPTION_MODE_INVALID).
+   * - 1
+     - 256-bit AES in XTS mode (ENCRYPTION_MODE_AES_256_XTS).
+   * - 2
+     - 256-bit AES in GCM mode (ENCRYPTION_MODE_AES_256_GCM).
+   * - 3
+     - 256-bit AES in CBC mode (ENCRYPTION_MODE_AES_256_CBC).
+
+Total size of the superblock is 1024 bytes.