LIBDM TASK

The libdm_task_create() function creates a libdm task dictionary with command string set to command. If command is NULL, libdm_task_t is not created and the function returns NULL.

libdm_task_destroy() free all memory allocated to libdm_task by libdm_task_create().

libdm_task_run() Sends created libdm_task to kernel and receives new one as reply.

List of attributes avaialable in libdm_task_t:

Attribute	Description	Mode
DM_IOCTL_OPEN	Device open-count	Read-Only
DM_IOCTL_MINOR	Device minor number	Read-Write
DM_IOCTL_NAME	Device name	Read-Write
DM_IOCTL_UUID	Device uuid	Read-Write
DM_IOCTL_TARGET_COUNT	Number of table entries	Read-Only
DM_IOCTL_FLAGS	Device status flags	Read-Write

libdm_task_set_name() and libdm_task_get_name() Set name of the device for commands which need to have a dm device identifier. The device-mapper later uses the device name to look up the device from the list of all devices. The get routine will fetch the device name from the task dictionary.

libdm_task_set_uuid() and libdm_task_get_uuid() Set uuid of device for commands which need to have a dm device identifier. The device-mapper later uses the device uuid to look up the device from the list of all devices. The get routine will fetch the device uuid from the task dictionary.

libdm_task_set_minor() and libdm_task_get_minor() Set minor device number of device for commands which need to have a dm device identifier. The device-mapper later uses the device minor number to look up the device from the list of all devices. The get routine will fetch the device minor number from the task dictionary.

libdm_task_set_flags() and libdm_task_get_flags() Set/fetch device status flags from the task dictionary.

libdm_task_get_open_num() Fetch number of opened devices from the kernel and return them as count.

libdm_task_get_target_num() Fetch number of opened devices from the kernel and return them as count.

libdm_task_get_cmd_version() Get the version of the dm driver in the kernel as array uint32_t *ver of size size. libdm_task_set_cmd() and libdm_task_get_cmd() Add and fetch cmd structure from libdm_task_t. libdm_cmd_t is the container used to carry information specific for the particular command. cmd is usually set before libdm_task_run is used and is taken from the task structure after the task run was called.

LIBDM TASK CMD

The libdm_cmd_create() function will allocate a cmd structure which can later be put in to the task.

libdm_cmd_destroy() will deallocate a previously allocated cmd structure.

libdm_cmd_set_table() Will load and fetch the device mapping table from the dm device. The table is usually loaded to the device during initial device creation or device resizing.

Because libdm_cmd is an array of structures, all _get routines need an iterator to work. For every entry we can have more than one. libdm_cmd_get_table() When the user creates a task with the "status" command, the kernel sends cmd with a table in it.

libdm_cmd_get_target() Get mapping target description from cmd. Target contains target_name and target_version.

libdm_cmd_get_dev() When user creates a task with the "info" command, the kernel sends cmd with information about dm device to user.

libdm_cmd_get_deps() When user creates a task with the "deps" command, the kernel sends cmd with an array of physical devices attached to the dm device.

Usually the device has more than one table entry in the device command. Therefore cmd iterators are needed for libdm_cmd_t; they can be created by the libdm_cmd_iter_create() function.

LIBDM CMD TABLE

A device table describes the logical mapping between the dm device and physical devices. Every table has the logical block start, the table length (in disk blocks), the target used by table, the physical device, and the offset on it. The physical device and the offset on it are parameters which are target specific and are passed down to the target as param string.

Example device table entry

0 1024 linear /dev/wd1a 384

Attribute	Description
DM_TABLE_TYPE	Used device mapper target
DM_TABLE_START	Device Logical start block
DM_TABLE_STAT	Is 1 if this is current active table
DM_TABLE_LENGTH	Logical length described by table
DM_TABLE_PARAMS	Params passed down to target

libdm_table_set_start() and libdm_table_get_start() Set start table from start value to libdm_table argument. Get routine will get the table start from kernel as libdm_table.

libdm_table_set_length() and libdm_table_get_length() Set table length from length value to libdm_table argument. Get routine will get the table length from kernel as libdm_table.

libdm_table_set_target() and libdm_table_get_target() Set target name from target value to libdm_table argument. The target must be actually present in the kernel, otherwise libdm_task_run() will fail. Get routine will get the table entry target from kernel as libdm_table.

libdm_table_set_params() and libdm_table_get_params() Set table target parameter string from params argument to libdm_table. This is later in the kernel passed to the target init routine. Get routine will get the table parameter string from kernel as libdm_table.

libdm_table_get_status() Get table status which can be Active/Inactive. This tells if this table is actually used or not.

LIBDM_TARGET

libdm_target_destroy() Destroy target received from libdm_cmd with libdm_cmd_iter iterator.

libdm_target_get_name() returns pointer to a string with available target name.

lobdm_target_get_version() Sets argument ver[3] to a in-kernel loaded target version.

LIBDM_DEV

libdm_dev_destroy() Destroy device received from libdm_cmd with libdm_cmd_iter iterator.

libdm_dev_get_name() Return pointer to a string with underlying device name from libdm_dev_t

libdm_dev_get_minor() Return underlying device minor number.

MISC

libdm_dev_set_newname() This routine will set new dm device name attribute to newname. User must then called libdm_task_run on this task to change the device name.