Linux Ext系列文件系统(看这一篇就够了!)

[root@localhost linux]# ls -l
总⽤量 12
-rwxr-xr-x. 1 root root 7438 "9⽉ 13 14:56" a.out
-rw-r--r--. 1 root root 654 "9⽉ 13 14:56" test.c

[root@localhost linux]# stat test.c
 File: "test.c"
 Size: 654 Blocks: 8 IO Block: 4096 普通⽂件
Device: 802h/2050d Inode: 263715 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2017-09-13 14:56:57.059012947 +0800
Modify: 2017-09-13 14:56:40.067012944 +0800
Change: 2017-09-13 14:56:40.069012948 +0800

/*
 * Structure of an inode on the disk
 */
struct ext2_inode {
 __le16 i_mode; /* File mode */
 __le16 i_uid; /* Low 16 bits of Owner Uid */
 __le32 i_size; /* Size in bytes */
 __le32 i_atime; /* Access time */
 __le32 i_ctime; /* Creation time */
 __le32 i_mtime; /* Modification time */
 __le32 i_dtime; /* Deletion Time */
 __le16 i_gid; /* Low 16 bits of Group Id */
 __le16 i_links_count; /* Links count */
 __le32 i_blocks; /* Blocks count */
 __le32 i_flags; /* File flags */
 union {
 struct {
 __le32 l_i_reserved1;
 } linux1;
 struct {
 __le32 h_i_translator;
 } hurd1;
 struct {
 __le32 m_i_reserved1;
 } masix1;
 } osd1; /* OS dependent 1 */
 __le32 i_block[EXT2_N_BLOCKS];/* Pointers to blocks */
 __le32 i_generation; /* File version (for NFS) */
 __le32 i_file_acl; /* File ACL */
 __le32 i_dir_acl; /* Directory ACL */
 __le32 i_faddr; /* Fragment address */
 union {
 struct {
 __u8 l_i_frag; /* Fragment number */
 __u8 l_i_fsize; /* Fragment size */
 __u16 i_pad1;
  __le16 l_i_uid_high; /* these 2 fields */
 __le16 l_i_gid_high; /* were reserved2[0] */
 __u32 l_i_reserved2;
 } linux2;
 struct {
 __u8 h_i_frag; /* Fragment number */
 __u8 h_i_fsize; /* Fragment size */
 __le16 h_i_mode_high;
 __le16 h_i_uid_high;
 __le16 h_i_gid_high;
 __le32 h_i_author;
 } hurd2;
 struct {
 __u8 m_i_frag; /* Fragment number */
 __u8 m_i_fsize; /* Fragment size */
 __u16 m_pad1;
 __u32 m_i_reserved2[2];
 } masix2;
 } osd2; /* OS dependent 2 */
};
/*
 * Constants relative to the data blocks
 */
#define EXT2_NDIR_BLOCKS 12
#define EXT2_IND_BLOCK EXT2_NDIR_BLOCKS
#define EXT2_DIND_BLOCK (EXT2_IND_BLOCK + 1)
#define EXT2_TIND_BLOCK (EXT2_DIND_BLOCK + 1)
#define EXT2_N_BLOCKS (EXT2_TIND_BLOCK + 1)
备注：EXT2_N_BLOCKS = 15

/*
 * 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; /* Free inodes count */
 __le32 s_first_data_block; /* 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; /* # Inodes per group */
 __le32 s_mtime; /* Mount time */
 __le32 s_wtime; /* Write time */
 __le16 s_mnt_count; /* Mount count */
 __le16 s_max_mnt_count; /* Maximal mount count */
 __le16 s_magic; /* Magic signature */
 __le16 s_state; /* File system state */
 __le16 s_errors; /* Behaviour when detecting errors */
 __le16 s_minor_rev_level; /* minor revision level */
 __le32 s_lastcheck; /* time of last check */
 __le32 s_checkinterval; /* max. time between checks */
 __le32 s_creator_os; /* OS */
 __le32 s_rev_level; /* Revision level */
 __le16 s_def_resuid; /* Default uid for reserved blocks */
 __le16 s_def_resgid; /* 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 */
 __le32 bg_inode_table; /* Inodes table block*/
 __le16 bg_free_blocks_count; /* 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

struct dentry {
 atomic_t d_count;
 unsigned int d_flags; /* protected by d_lock */
 spinlock_t d_lock; /* per dentry lock */
 struct inode *d_inode; /* Where the name belongs to - NULL is
 * negative */
 /*
 * The next three fields are touched by __d_lookup. Place them here
 * so they all fit in a cache line.
 */
 struct hlist_node d_hash; /* lookup hash list */
 struct dentry *d_parent; /* parent directory */
 struct qstr d_name;
 struct list_head d_lru; /* LRU list */
 /*
 * d_child and d_rcu can share memory
 */
 union {
 struct list_head d_child; /* child of parent list */
 struct rcu_head d_rcu;
 } d_u;
 struct list_head d_subdirs; /* our children */
 struct list_head d_alias; /* inode alias list */
 unsigned long d_time; /* used by d_revalidate */
 struct dentry_operations *d_op;
 struct super_block *d_sb; /* The root of the dentry tree */
 void *d_fsdata; /* fs-specific data */
#ifdef CONFIG_PROFILING
 struct dcookie_struct *d_cookie; /* cookie, if any */
#endif
 int d_mounted;
 unsigned char d_iname[DNAME_INLINE_LEN_MIN]; /* small names */
};

$ dd if=/dev/zero of=./disk.img bs=1M count=5 #制作⼀个⼤的磁盘块，就当做⼀个分区 
$ mkfs.ext4 disk.img # 格式化写⼊⽂件系统 
$ mkdir /mnt/mydisk # 建⽴空⽬录 
$ df -h # 查看可以使⽤的分区 
Filesystem Size Used Avail Use% Mounted on
udev 956M 0 956M 0% /dev
tmpfs 198M 724K 197M 1% /run
/dev/vda1 50G 20G 28G 42% /
tmpfs 986M 0 986M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 986M 0 986M 0% /sys/fs/cgroup
tmpfs 198M 0 198M 0% /run/user/0
tmpfs 198M 0 198M 0% /run/user/1002
$ sudo mount -t ext4 ./disk.img /mnt/mydisk/ # 将分区挂载到指定的⽬录 
$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 956M 0 956M 0% /dev
tmpfs 198M 724K 197M 1% /run
/dev/vda1 50G 20G 28G 42% /
tmpfs 986M 0 986M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 986M 0 986M 0% /sys/fs/cgroup
tmpfs 198M 0 198M 0% /run/user/0
tmpfs 198M 0 198M 0% /run/user/1002
/dev/loop0 4.9M 24K 4.5M 1% /mnt/mydisk
$ sudo umount /mnt/mydisk # 卸载分区 
whb@bite:/mnt$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 956M 0 956M 0% /dev
tmpfs 198M 724K 197M 1% /run
/dev/vda1 50G 20G 28G 42% /
tmpfs 986M 0 986M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 986M 0 986M 0% /sys/fs/cgroup
tmpfs 198M 0 198M 0% /run/user/0
tmpfs 198M 0 198M 0% /run/user/1002