【linux学习指南】】Ext系列文件系统(三)ext2 文件系统的认识与构成

/*
 * Structure of the super block
 */
struct ext2_super_block
{
    __le32 s_inodes_count;
    /* Inodes count */
    __le32 s_blocks_count;
    /* Blocks count */
    __le32 s_r_blocks_count; /* Reserved blocks count */
    __le32 s_free_blocks_count;
    /* Free blocks count */
    __le32 s_free_inodes_count;
    __le32 s_first_data_block;
    /* Free inodes count */
    /* First Data Block */
    __le32 s_log_block_size; /* Block size */
    __le32 s_log_frag_size;
    /* Fragment size */
    __le32 s_blocks_per_group;
    /* # Blocks per group */
    __le32 s_frags_per_group; /* # Fragments per group */
    __le32 s_inodes_per_group;
    __le32 s_mtime;
    __le32 s_wtime;
    __le16 s_mnt_count;
    /* # Inodes per group */
    /* Mount time */
    /* Write time */
    /* Mount count */
    __le16 s_max_mnt_count;
    __le16 s_magic;
    __le16 s_state;
    __le16 s_errors;
    /* Maximal mount count */
    /* Magic signature */
    /* File system state */
    /* Behaviour when detecting errors */
    __le16 s_minor_rev_level; /* minor revision level */
    __le32 s_lastcheck;
    __le32 s_checkinterval;
    __le32 s_creator_os;
    __le32 s_rev_level;
    __le16 s_def_resuid;
    __le16 s_def_resgid;
    /* time of last check */
    /* max. time between checks */
    /* OS */
    /* Revision level */
    /* Default uid for reserved blocks */
    /* Default gid for reserved blocks */
    /*
     * These fields are for EXT2_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...
     */
    __le32 s_first_ino;              /* First non-reserved inode */
    __le16 s_inode_size;             /* size of inode structure */
    __le16 s_block_group_nr;         /* block group # of this superblock */
    __le32 s_feature_compat;         /* compatible feature set */
    __le32 s_feature_incompat;       /* incompatible feature set */
    __le32 s_feature_ro_compat;      /* readonly-compatible feature set */
    __u8 s_uuid[16];                 /* 128-bit uuid for volume */
    char s_volume_name[16];          /* volume name */
    char s_last_mounted[64];         /* directory where last mounted */
    __le32 s_algorithm_usage_bitmap; /* For compression */
    /*
     * Performance hints.  Directory preallocation should only
     * happen if the EXT2_COMPAT_PREALLOC flag is on.
     */
    __u8 s_prealloc_blocks;     /* Nr of blocks to try to preallocate*/
    __u8 s_prealloc_dir_blocks; /* Nr to preallocate for dirs */
    __u16 s_padding1;
    /*
     * Journaling support valid if EXT3_FEATURE_COMPAT_HAS_JOURNAL set.
     */
    __u8 s_journal_uuid[16]; /* uuid of journal superblock */
    __u32 s_journal_inum;    /* inode number of journal file */
    __u32 s_journal_dev;     /* device number of journal file */
    __u32 s_last_orphan;     /* start of list of inodes to delete */
    __u32 s_hash_seed[4];    /* HTREE hash seed */
    __u8 s_def_hash_version; /* Default hash version to use */
    __u8 s_reserved_char_pad;
    __u16 s_reserved_word_pad;
    __le32 s_default_mount_opts;
    __le32 s_first_meta_bg; /* First metablock block group */
    __u32 s_reserved[190];  /* Padding to the end of the block */
};

// 磁盘级blockgroup的数据结构
/*
 * Structure of a blocks group descriptor
 */
struct ext2_group_desc
{
    __le32 bg_block_bitmap;/* Blocks bitmap block */
    __le32 bg_inode_bitmap;/* Inodes bitmap */
    __le16 bg_free_blocks_count; /* Inodes table block*/
    __le32 bg_inode_table;/* Free blocks count */
    __le16 bg_free_inodes_count;/* Free inodes count */
    __le16 bg_used_dirs_count; /* Directories count */
    __le16 bg_pad;
    __le32 bg_reserved[3];
};

[root@localhost linux]# touch abc
 [root@localhost linux]# ls -i abc
 263466 abc