Understanding the Linux Kernel

12.2. VFS Data Structures

Each VFS object is stored in a suitable data structure, which includes both the object attributes and a pointer to a table of object methods. The kernel may dynamically modify the methods of the object, and hence it may install specialized behavior for the object. The following sections explain the VFS objects and their interrelationships in detail.

12.2.1. Superblock Objects

A superblock object consists of a super_block structure whose fields are described in Table 12-2.

Table 12-2. The Fields of the Superblock Object

Type	Field	Description
struct list_head	s_list	Pointers for superblock list
kdev_t	s_dev	Device identifier
unsigned long	s_blocksize	Block size in bytes
unsigned char	s_blocksize_bits	Block size in number of bits
unsigned char	s_lock	Lock flag
unsigned char	s_rd_only	Read-only flag
unsigned char	s_dirt	Modified (dirty) flag
struct file_system_type *	s_type	Filesystem type
struct super_operations *	s_op	Superblock methods
struct dquot_operations *	dq_op	Disk quota methods
unsigned long	s_flags	Mount flags
unsigned long	s_magic	Filesystem magic number
unsigned long	s_time	Time of last superblock change
struct dentry *	s_root	Dentry object of mount directory
struct wait_queue *	s_wait	Mount wait queue
struct inode *	s_ibasket	Future development
short int	s_ibasket_count	Future development
short int	s_ibasket_max	Future development
struct list_head	s_dirty	List of modified inodes
union	u	Specific filesystem information

All superblock objects ...