系统中注册的 target_type 都链入 static LIST_HEAD(_targets) 中
int dm_register_target(struct target_type *tt) 向系统中注册 target_type，如果之前已经注册过了则返回 -EEXIST，否则成功注册并返回 0
void dm_unregister_target(struct target_type *tt) 从系统中注销 target_type，如果之前没有注册过，则报错 Unregistering unrecognised target: <target_type->name> 并 BUG()，否则移出 static LIST_HEAD(_targets)
int dm_target_iterate(void (*iter_func)(struct target_type *tt, void *param), void *param) 对系统中注册的每个 target_type 执行 iter_func(target_type, param)。这个函数在执行 dmsetup targets 时会用到
struct target_type *dm_get_target_type(const char *name) 查找指定 name 对应的 target_type 并将对应的 dm-void dm_put_target_type(struct target_type *tt) 将 target_type 对应的 dm-
struct target_type
/*
* Information about a target type
*/
struct target_type {
uint64_t features;
const char *name;
struct module *module;
unsigned version[3];
dm_ctr_fn ctr;
dm_dtr_fn dtr;
dm_map_fn map;
dm_clone_and_map_request_fn clone_and_map_rq;
dm_release_clone_request_fn release_clone_rq;
dm_endio_fn end_io;
dm_request_endio_fn rq_end_io;
dm_presuspend_fn presuspend;
dm_presuspend_undo_fn presuspend_undo;
dm_postsuspend_fn postsuspend;
dm_preresume_fn preresume;
dm_resume_fn resume;
dm_status_fn status;
dm_message_fn message;
dm_prepare_ioctl_fn prepare_ioctl;
dm_busy_fn busy;
dm_iterate_devices_fn iterate_devices;
dm_io_hints_fn io_hints;
dm_dax_direct_access_fn direct_access;
dm_dax_copy_iter_fn dax_copy_from_iter;
dm_dax_copy_iter_fn dax_copy_to_iter;
/* For internal device-mapper use. */
struct list_head list; 链入 _targets 链表
};
Target features
/*
* Any table that contains an instance of this target must have only one.
*/
#define DM_TARGET_SINGLETON 0x00000001
#define dm_target_needs_singleton(type) ((type)->features & DM_TARGET_SINGLETON)
/*
* Indicates that a target does not support read-only devices.
*/
#define DM_TARGET_ALWAYS_WRITEABLE 0x00000002
#define dm_target_always_writeable(type) ((type)->features & DM_TARGET_ALWAYS_WRITEABLE)
/*
* Any device that contains a table with an instance of this target may never
* have tables containing any different target type.
*/
#define DM_TARGET_IMMUTABLE 0x00000004
#define dm_target_is_immutable(type) ((type)->features & DM_TARGET_IMMUTABLE)
/*
* Indicates that a target may replace any target; even immutable targets.
* .map, .map_rq, .clone_and_map_rq and .release_clone_rq are all defined.
*/
#define DM_TARGET_WILDCARD 0x00000008
#define dm_target_is_wildcard(type) ((type)->features & DM_TARGET_WILDCARD)
/*
* A target implements own bio data integrity.
*/
#define DM_TARGET_INTEGRITY 0x00000010
#define dm_target_has_integrity(type) ((type)->features & DM_TARGET_INTEGRITY)
/*
* A target passes integrity data to the lower device.
*/
#define DM_TARGET_PASSES_INTEGRITY 0x00000020
#define dm_target_passes_integrity(type) ((type)->features & DM_TARGET_PASSES_INTEGRITY)
/*
* Indicates that a target supports host-managed zoned block devices.
*/
#define DM_TARGET_ZONED_HM 0x00000040
#define dm_target_supports_zoned_hm(type) ((type)->features & DM_TARGET_ZONED_HM)