text: /*
   * loop.h
   *
   * Written by Theodore Ts'o, 3/29/93.
   *
   * Copyright 1993 by Theodore Ts'o.  Redistribution of this file is
   * permitted under the GNU General Public License.
   */
  #ifndef _LINUX_LOOP_H
  #define _LINUX_LOOP_H
  
  #include <linux/bio.h>
  #include <linux/blkdev.h>
  #include <linux/blk-mq.h>
  #include <linux/spinlock.h>
  #include <linux/mutex.h>
  #include <linux/kthread.h>
  #include <uapi/linux/loop.h>
  
  /* Possible states of device */
  enum {
  	Lo_unbound,
  	Lo_bound,
  	Lo_rundown,
  };
  
  struct loop_func_table;
  
  struct loop_device {
  	int		lo_number;
  	atomic_t	lo_refcnt;
  	loff_t		lo_offset;
  	loff_t		lo_sizelimit;
  	int		lo_flags;
  	int		(*transfer)(struct loop_device *, int cmd,
  				    struct page *raw_page, unsigned raw_off,
  				    struct page *loop_page, unsigned loop_off,
  				    int size, sector_t real_block);
  	char		lo_file_name[LO_NAME_SIZE];
  	char		lo_crypt_name[LO_NAME_SIZE];
  	char		lo_encrypt_key[LO_KEY_SIZE];
  	int		lo_encrypt_key_size;
  	struct loop_func_table *lo_encryption;
  	__u32           lo_init[2];
  	kuid_t		lo_key_owner;	/* Who set the key */
  	int		(*ioctl)(struct loop_device *, int cmd, 
  				 unsigned long arg); 
  
  	struct file *	lo_backing_file;
  	struct block_device *lo_device;
  	void		*key_data; 
  
  	gfp_t		old_gfp_mask;
  
  	spinlock_t		lo_lock;
  	int			lo_state;
  	struct mutex		lo_ctl_mutex;
  	struct kthread_worker	worker;
  	struct task_struct	*worker_task;
  	bool			use_dio;
  
  	struct request_queue	*lo_queue;
  	struct blk_mq_tag_set	tag_set;
  	struct gendisk		*lo_disk;
  };
  
  struct loop_cmd {
  	struct kthread_work work;
  	bool use_aio; /* use AIO interface to handle I/O */
  	atomic_t ref; /* only for aio */
  	long ret;
  	struct kiocb iocb;
  	struct bio_vec *bvec;
  	struct cgroup_subsys_state *css;
  };
  
  /* Support for loadable transfer modules */
  struct loop_func_table {
  	int number;	/* filter type */ 
  	int (*transfer)(struct loop_device *lo, int cmd,
  			struct page *raw_page, unsigned raw_off,
  			struct page *loop_page, unsigned loop_off,
  			int size, sector_t real_block);
  	int (*init)(struct loop_device *, const struct loop_info64 *); 
  	/* release is called from loop_unregister_transfer or clr_fd */
  	int (*release)(struct loop_device *); 
  	int (*ioctl)(struct loop_device *, int cmd, unsigned long arg);
  	struct module *owner;
  }; 
  
  int loop_register_transfer(struct loop_func_table *funcs);
  int loop_unregister_transfer(int number); 
  
  #endif
  