devicemapper源码理解

device-mapper.h

table的类型，mapped_device 的内存池和请求队列
enum dm_queue_mode {
DM_TYPE_NONE = 0,
DM_TYPE_BIO_BASED = 1,
DM_TYPE_REQUEST_BASED = 2,
DM_TYPE_MQ_REQUEST_BASED = 3,
DM_TYPE_DAX_BIO_BASED = 4,
};

一些函数原型如：
typedef int (dm_ctr_fn) (struct dm_target target,
unsigned int argc, char **argv);

/*

• The map function must return:
• < 0: error
• = 0: The target will handle the io by resubmitting it later
• = 1: simple remap complete
• = 2: The target wants to push back the io
  /
  typedef int (dm_map_fn) (struct dm_target ti, struct bio bio);

/*

• Returns:
• < 0 : error (currently ignored)
• 0 : ended successfully
• 1 : for some reason the io has still not completed (eg,
• multipath target might want to requeue a failed io).
• 2 : The target wants to push back the io
  /
  typedef int (dm_endio_fn) (struct dm_target *ti,

  struct bio *bio, int error);
  

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_map_request_fn map_rq;
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_merge_fn merge;
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_memcpy_fromiovecend_fn dax_memcpy_fromiovecend;
dm_dax_memcpy_toiovecend_fn dax_memcpy_toiovecend;

/* For internal device-mapper use. */
struct list_head list;

};

2020-4-5
从devicemapper 初始化开始看：
在dm-ioctl.c中
创建混杂设备(混杂设备是一种字符设备)：

int __init dm_interface_init(void)
{
	int r;

	r = dm_hash_init();
	if (r)
		return r;

	r = misc_register(&_dm_misc); //注册混杂设备
	if (r) {
		DMERR("misc_register failed for control device");
		dm_hash_exit();
		return r;
	}

	DMINFO("%d.%d.%d%s initialised: %s", DM_VERSION_MAJOR,
	       DM_VERSION_MINOR, DM_VERSION_PATCHLEVEL, DM_VERSION_EXTRA,
	       DM_DRIVER_EMAIL);
	return 0;
}

在dm.c 调用并初始化

static struct miscdevice _dm_misc = {
	.minor		= MAPPER_CTRL_MINOR,
	.name  		= DM_NAME,
	.nodename	= DM_DIR "/" DM_CONTROL_NODE,
	.fops  		= &_ctl_fops //设置混杂设备的一些操作
};

混杂设备具体的操作：

static const struct file_operations _ctl_fops = {
	.open    = dm_open,
	.release = dm_release,
	.poll    = dm_poll,
	.unlocked_ioctl	 = dm_ctl_ioctl,
	.compat_ioctl = dm_compat_ctl_ioctl,
	.owner	 = THIS_MODULE,
	.llseek  = noop_llseek,
};

在dm_ctl_ioctl中实现具体的ioctl操作
dm_ctl_ioctl() -> ctl_ioctl() -> lookup_ioctl() //查找对应的ioctl操作
在 ctl_ioctl中执行对应的ioctl操作

static ioctl_fn lookup_ioctl(unsigned int cmd, int *ioctl_flags)
{
	static const struct {
		int cmd;
		int flags;
		ioctl_fn fn;
	} _ioctls[] = {
		{DM_VERSION_CMD, 0, NULL}, /* version is dealt with elsewhere */
		{DM_REMOVE_ALL_CMD, IOCTL_FLAGS_NO_PARAMS | IOCTL_FLAGS_ISSUE_GLOBAL_EVENT, remove_all},
		{DM_LIST_DEVICES_CMD, 0, list_devices},

		{DM_DEV_CREATE_CMD, IOCTL_FLAGS_NO_PARAMS | IOCTL_FLAGS_ISSUE_GLOBAL_EVENT, dev_create},
		{DM_DEV_REMOVE_CMD, IOCTL_FLAGS_NO_PARAMS | IOCTL_FLAGS_ISSUE_GLOBAL_EVENT, dev_remove},
		{DM_DEV_RENAME_CMD, IOCTL_FLAGS_ISSUE_GLOBAL_EVENT, dev_rename},
		{DM_DEV_SUSPEND_CMD, IOCTL_FLAGS_NO_PARAMS, dev_suspend},
		{DM_DEV_STATUS_CMD, IOCTL_FLAGS_NO_PARAMS, dev_status},
		{DM_DEV_WAIT_CMD, 0, dev_wait},

		{DM_TABLE_LOAD_CMD, 0, table_load},
		{DM_TABLE_CLEAR_CMD, IOCTL_FLAGS_NO_PARAMS, table_clear},
		{DM_TABLE_DEPS_CMD, 0, table_deps},
		{DM_TABLE_STATUS_CMD, 0, table_status},

		{DM_LIST_VERSIONS_CMD, 0, list_versions},

		{DM_TARGET_MSG_CMD, 0, target_message},
		{DM_DEV_SET_GEOMETRY_CMD, 0, dev_set_geometry},
		{DM_DEV_ARM_POLL, IOCTL_FLAGS_NO_PARAMS, dev_arm_poll},
	};

	if (unlikely(cmd >= ARRAY_SIZE(_ioctls)))
		return NULL;

	*ioctl_flags = _ioctls[cmd].flags;
	return _ioctls[cmd].fn;
}

看一下创建一个mapping device的过程：

static int dev_create(struct file *filp, struct dm_ioctl *param, size_t param_size)
{
	int r, m = DM_ANY_MINOR;
	struct mapped_device *md;

	r = check_name(param->name);
	if (r)
		return r;

	if (param->flags & DM_PERSISTENT_DEV_FLAG)
		m = MINOR(huge_decode_dev(param->dev));

	r = dm_create(m, &md);
	if (r)
		return r;

	r = dm_hash_insert(param->name, *param->uuid ? param->uuid : NULL, md);
	if (r) {
		dm_put(md);
		dm_destroy(md);
		return r;
	}

	param->flags &= ~DM_INACTIVE_PRESENT_FLAG;

	__dev_status(md, param);

	dm_put(md);

	return 0;
}