[File system] File System learning Note (ix)---ROOTFS

One: Root file System (ROOTFS)

Registration of the 1,rootfs file system
In the Linux kernel initialization phase, an int __init init_rootfs (void) is called to register the Rootfs file system with the kernel.
The function of the core of Init_rootfs () is Register_filesystem (); This function registers the structure File_system_type in a single linked list of the kernel,

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2. 307 int __init init_rootfs (void)
4. 308 {
6. 309 int err;
8. 311 err = Bdi_init (&ramfs_backing_dev_info);
10. 312 if (err)
12. 313 return err;
14. 315 err = Register_filesystem (&rootfs_fs_type);
16. if (err)
18. 317 Bdi_destroy (&ramfs_backing_dev_info);
20. 319 return err;
22. 320}
26. 288 static struct File_system_type Rootfs_fs_type = {
28. 289. Name = "Rootfs",
30. 290. Mount = Rootfs_mount,
32. 291. KILL_SB = Kill_litter_super,
34. 292};

2,rootfs_mount () function parsing
static struct Dentry *rootfs_mount (struct file_system_type *fs_type, int flags, const char *dev_name, void *data)
The Rootfs_mount () function first calls the Mount_nodev () function, and the Mount_nodev () function is prototyped as follows: Mount_nodev (Fs_type, Flags, data, ramfs_fill_super);

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2. 1060 struct dentry *mount_nodev (struct file_system_type *fs_type,
4. 1061 int flags, void *data,
6. 1062 Int (*fill_super) (struct super_block *, void *, int))
8. 1063 {
10. 1064 int error;
12. 1065 struct Super_block *s = sget (Fs_type, NULL, set_anon_super, NULL);
14. 1067 if (Is_err (s))
16. 1068 return Err_cast (s);
18. 1069
20. 1070 s->s_flags = flags;
22. 1072 error = Fill_super (s, data, Flags & ms_silent? 1:0);
24. 1073 if (error) {
26. 1074 Deactivate_locked_super (s);
28. 1075 return err_ptr (Error);
30. 1076}
32. 1077 S->s_flags |= ms_active;
34. 1078 return Dget (s->s_root);
36. 1079}

The function of the Sget () function of the above functions is mainly to allocate a super fast (Super_block) instance, and. Join the list super_blocks by S_list and then join the list s_instances by Typer->fs_supers.

The Fill_super () function is called to the Ramfs_fill_super () function, and the Ramfs_fill_super () function is defined as follows:

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2. 209 int Ramfs_fill_super (struct super_block *sb, void *data, int silent)
4. 210 {
6. 211 struct Ramfs_fs_info *fsi;
8. 212 struct Inode *inode;
10. 213 int Err;
12. 215 save_mount_options (SB, data);
14. 217 FSI = Kzalloc (sizeof (struct ramfs_fs_info), gfp_kernel);
16. 218 Sb->s_fs_info = FSI;
18. 219 if (!FSI)
20. Return-enomem;
22. 222 Err = ramfs_parse_options (data, &fsi->mount_opts);
24. 223 if (err)
26. 224 return err;
28. 226 sb->s_maxbytes = max_lfs_filesize; //maximum value of the file
30. 227 sb->s_blocksize = page_cache_size; //The size of the block in bytes
32. 228 sb->s_blocksize_bits = Page_cache_shift; //The size of the block in bits
34. 229 sb->s_magic = ramfs_magic;
36. Sb->s_op = &ramfs_ops; //Super Block method, which will be useful when dealing with the Inode
38. 231 Sb->s_time_gran = 1;
40. 233 inode = Ramfs_get_inode (SB, NULL, S_ifdir | fsi->mount_opts.mode, 0); //Establish root index node
42. 234 sb->s_root = D_make_root (inode); //Establish the root directory object; The s_root of the Super block points to the newly created root directory object
44. 235 if (!sb->s_root)
46. 236 Return-enomem;
48. 238 return 0;
50. 239}
54. the *ramfs_get_inode-struct inode (struct super_block *sb,
56. const struct inode *dir, umode_t mode, dev_t Dev)
58. 56 {
60. The inode of the new_inode struct, inode = (SB); //Create an inode in the index node cache,
62. if (inode) {
64. Inode->i_ino = Get_next_ino (); //Get an inode number
66. Inode_init_owner (Inode, dir, mode); //Set Inode, initialize UID GID mode, etc.
68. Inode->i_mapping->a_ops = &ramfs_aops;
70. Inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
72. Mapping_set_gfp_mask (inode->i_mapping, Gfp_highuser);
74. Mapping_set_unevictable (inode->i_mapping);
76. Inode->i_atime = Inode->i_mtime = Inode->i_ctime = Current_time;
78. (Mode & s_ifmt) {
80. default: //Special files such as: Character ~ block device file, fifo,socket file
82. Init_special_inode (inode, mode, dev);
84. a break ;
86. S_ifreg Case: //Normal file
88. Inode->i_op = &ramfs_file_inode_operations;
90. INODE->I_FOP = &ramfs_file_operations;
92. a break ;
94. s_ifdir Case: //directory file
96. Inode->i_op = &ramfs_dir_inode_operations;
98. INODE->I_FOP = &simple_dir_operations;
100. */* directory inodes start off with i_nlink = = 2 (for "." entry) */
102. Inc_nlink (Inode);
104. Bayi break ;
106. S_iflnk Case: //link file
108. Inode->i_op = &page_symlink_inode_operations;
110. a break ;
112. 85}
114. 86}
116. The return of the inode; //Returns the created Inode associated with the corresponding Catalog item object
118. 88}

[File system] File System learning Note (ix)---ROOTFS