Linux File System and nginx module system are similar

In Linux, inode is operated through the file_operation struct. All fields of the file_operation struct are pointer structures. Each file system must implement these methods for the system to call. For the system, if you do not know which file system you want to operate, you only need to call the interface method. The file_operation function pointer will naturally pass the initialization process, call the corresponding method of the corresponding file system.

In this way, file_operation seems to be a collection of multiple interface methods. The real file system only needs to implement the response method, and corresponds to the function pointer, it can be used after initialization.

The following is the structure code of file_operation. If you do not need or cannot use a function pointer, you can set it to null.

struct file_operations {struct module *owner;loff_t (*llseek) (struct file *, loff_t, int);ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);int (*readdir) (struct file *, void *, filldir_t);unsigned int (*poll) (struct file *, struct poll_table_struct *);int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);long (*compat_ioctl) (struct file *, unsigned int, unsigned long);int (*mmap) (struct file *, struct vm_area_struct *);int (*open) (struct inode *, struct file *);int (*flush) (struct file *, fl_owner_t id);int (*release) (struct inode *, struct file *);int (*fsync) (struct file *, struct dentry *, int datasync);int (*aio_fsync) (struct kiocb *, int datasync);int (*fasync) (int, struct file *, int);int (*lock) (struct file *, int, struct file_lock *);ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);int (*check_flags)(int);int (*flock) (struct file *, int, struct file_lock *);ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);int (*setlease)(struct file *, long, struct file_lock **);};

Similarly, there are structures such as inode_operation.

Next, let's look at the module system of nginx. In order to reduce the coupling between the module and nginx and improve the system plasticity. Nginx also uses this object-oriented "Interface Class" method to implement the module system.

typedef struct {    ngx_str_t              *name;    void                 *(*create_conf)(ngx_cycle_t *cycle);    char                 *(*init_conf)(ngx_cycle_t *cycle, void *conf);    ngx_event_actions_t     actions;} ngx_event_module_t;typedef struct {    ngx_int_t  (*add)(ngx_event_t *ev, ngx_int_t event, ngx_uint_t flags);    ngx_int_t  (*del)(ngx_event_t *ev, ngx_int_t event, ngx_uint_t flags);    ngx_int_t  (*enable)(ngx_event_t *ev, ngx_int_t event, ngx_uint_t flags);    ngx_int_t  (*disable)(ngx_event_t *ev, ngx_int_t event, ngx_uint_t flags);    ngx_int_t  (*add_conn)(ngx_connection_t *c);    ngx_int_t  (*del_conn)(ngx_connection_t *c, ngx_uint_t flags);    ngx_int_t  (*process_changes)(ngx_cycle_t *cycle, ngx_uint_t nowait);    ngx_int_t  (*process_events)(ngx_cycle_t *cycle, ngx_msec_t timer,                   ngx_uint_t flags);    ngx_int_t  (*init)(ngx_cycle_t *cycle, ngx_msec_t timer);    void       (*done)(ngx_cycle_t *cycle);} ngx_event_actions_t;

See how similar they are. You only need to implement the interface methods contained in the event_action structure to implement the functions of your own modules.