https://blog.csdn.net/sunlei0625/article/details/79011946

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:

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 ^ s_log_cluster_size) blocks if bigalloc is enabled, zero otherwise.
0x20 __le32 s_blocks_per_group Blocks per group.
0x24 __le32 s_clusters_per_group Clusters per group, if bigalloc is enabled.
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. Valid values are:

0x0001 Cleanly umounted
0x0002 Errors detected
0x0004 Orphans being recovered
0x3C __le16 s_errors Behaviour when detecting errors. One of:

1 Continue
2 Remount read-only
3 Panic
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 OS. One of:

0 Linux
1 Hurd
2 Masix
3 FreeBSD
4 Lites
0x4C __le32 s_rev_level Revision level. One of:

0 Original format
1 v2 format w/ dynamic inode sizes
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. Any of:

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).
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).
0x60 __le32 s_feature_incompat Incompatible feature set. If the kernel or fsck doesn't understand one of these bits, it should stop. Any of:

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. Not implemented (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).
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. Any of:

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 (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)
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.
Journaling support valid if EXT4_FEATURE_COMPAT_HAS_JOURNAL 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. One of:

0x0 Legacy.
0x1 Half MD4.
0x2 Tea.
0x3 Legacy, unsigned.
0x4 Half MD4, unsigned.
0x5 Tea, unsigned.
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. Any of:

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)
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 valid if EXT4_FEATURE_COMPAT_64BIT
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. Any of:

0x0001 Signed directory hash in use.
0x0002 Unsigned directory hash in use.
0x0004 To test development code.
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 file.
0x244 __le32 s_grp_quota_inum Inode number of group 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 below:

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).
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 __le32 s_reserved[98] Padding to the end of the block.
0x3FC __le32 s_checksum Superblock checksum.

Total size is 1024 bytes.

EXT4 超级块介绍(转)的更多相关文章

  1. linux操作系统故障处理-ext4文件系统超级块损坏修复

    linux操作系统故障处理-ext4文件系统超级块损坏修复   背景 前天外面出差大数据测试环境平台有7台服务器挂了,同事重启好了五台服务器,但是还有两台服务器启动不起来,第二天回来后我和同事再次去机 ...

  2. Linux 文件系统错误的修复方法 ddrescue替代dd的恢复软件 备用超级块

    Linux 文件系统错误的修复方法  ddrescue替代dd的恢复软件  备用超级块 最近处理的一件 linux 服务器断电导致文件系统启动后文件系统不可读写,数据不可用的案例,现总结下 Linux ...

  3. Linux 虚拟文件系统四大对象:超级块、inode、dentry、file之间关系

    更多嵌入式原创文章,请关注公众号:一口Linux 一:文件系统 1. 什么是文件系统? 操作系统中负责管理和存储文件信息的软件机构称为文件管理系统,简称文件系统. 通常文件系统是用于存储和组织文件的一 ...

  4. 81 dumpe2fs-打印“ext2/ext3”文件系统的超级块和快组信息

    dumpe2fs打印"ext2/ext3"文件系统的超级块和快组信息. 语法 dumpe2fs (选项) (参数) 选项 -b:打印文件系统中预留的块信息: -ob<超级块& ...

  5. 从ext2文件系统上读出超级块

    概述            本篇博客中,我们将仔细分析如何从格式化为ext2文件系统的磁盘中读取超级块并填充内存超级块结构,每次将一个格式化了ext2文件系统的磁盘(分区)挂载到挂载点的时候会调用该方 ...

  6. itop4412学习-超级块操作

    1. 先看下超级块支持的函数列表,文件路径\4412_SCP精英版\Android源码\iTop4412_Kernel_3.0_20140521\iTop4412_Kernel_3.0\include ...

  7. 一步一步粗谈linux文件系统(三)----超级块(superblock)【转】

    本文转载自:https://blog.csdn.net/fenglifeng1987/article/details/8302921 超级块是来描述整个文件系统信息的,可以说是一个全局的数据结构,可以 ...

  8. 文件系统VFS数据结构(超级块 inode dentry file)(收集整理)

    Linux虚拟文件系统四大对象: 1)超级块(super block) 2)索引节点(inode) 3)目录项(dentry) 4)文件对象(file) 一个进程在对一个文件进行操作时各种对象的引用过 ...

  9. 超级块,i节点,数据块,目录块,间接块

    一.物理磁盘到文件系统 文件系统用来存储文件内容,文件属性,和目录,这些类型的数据如何存储在磁盘块上的呢?Unix/linux使用了一个简单的方法. 他将磁盘分为3个部分: 超级块,文件系统中第一个块 ...

随机推荐

  1. Qt 查询字符串数据

    (1)函数QString::startsWith(),判断某一个字符串是否以某个字符串开头:该函数具有两个参数,第一个参数制定了一个字符串,第二个参数指定是否大小写敏感,默认大小写敏感: eg: QS ...

  2. Oracle数据库三种备份方案

    Oracle数据库有三种标准的备份方法,它们分别是导出/导入(EXP/IMP).热备份和冷备份.导出备件是一种逻辑备份,冷备份和热备份是物理备份. 一. 导出/导入(Export/Import) 利用 ...

  3. ios初识UITableView及简单用法二(模型数据)

    // // ViewController.m // ZQRTableViewTest // // Created by zzqqrr on 17/8/24. // Copyright (c) 2017 ...

  4. Debugging memory usage with kbmMW

    kbmMW的更高版本包含越来越多的功能,可用于通常的日志记录,审计,运行期发生异常时的堆栈跟踪以及现在的内存使用调试.这些功能实际上可用于任何应用程序,不仅限于基于kbmMW开发的多层应用系统.我已经 ...

  5. Day9作业及默写

    1,整理函数相关知识点,写博客. 2,写函数,检查获取传入列表或元组对象的所有奇数位索引对应的元素,并将其作为新列表返回给调用者. def func(obj): return obj[1::2] 3, ...

  6. ie 折腾计(浏览器兼容性)

    常见问题 IE:6.0,IE7.0,IE8.0之间的兼容独立说明 /*用于展示标签*/ <div class="jrx"></div> <style ...

  7. Python 实例方法

    class Computer: # 实例方法 def play(self): print("电脑可以扫雷") # 在定义实例方法的时候. 必须给出一个参数 self # 形参的第一 ...

  8. HDU 1846 Brave Game(巴什博弈超简单题)

    题目传送:http://acm.hdu.edu.cn/showproblem.php?pid=1846 Problem Description 十年前读大学的时候,中国每年都要从国外引进一些电影大片, ...

  9. 2.3 xpath定位

    2.3 xpath定位 前言    在上一篇简单的介绍了用工具查看目标元素的xpath地址,工具查看比较死板,不够灵活,有时候直接复制粘贴会定位不到.这个时候就需要自己手动的去写xpath了,这一篇详 ...

  10. make clean,make distclean与make depend的区别

    make clean仅仅是清除之前编译的可执行文件及配置文件. 而make distclean要清除所有生成的文件. Makefile 在符合GNU Makefiel惯例的Makefile中,包含了一 ...