Sequential state machine: libfprint Reference Manual

Sequential state machine

Sequential state machine — State machine helpers

Functions

void	(*FpiSsmCompletedCallback) ()
void	(*FpiSsmHandlerCallback) ()
#define	fpi_ssm_new()
FpiSsm *	fpi_ssm_new_full ()
void	fpi_ssm_free ()
void	fpi_ssm_start ()
void	fpi_ssm_start_subsm ()
void	fpi_ssm_next_state ()
void	fpi_ssm_next_state_delayed ()
void	fpi_ssm_jump_to_state ()
void	fpi_ssm_jump_to_state_delayed ()
void	fpi_ssm_cancel_delayed_state_change ()
void	fpi_ssm_mark_completed ()
void	fpi_ssm_mark_failed ()
void	fpi_ssm_set_data ()
gpointer	fpi_ssm_get_data ()
FpDevice *	fpi_ssm_get_device ()
GError *	fpi_ssm_get_error ()
GError *	fpi_ssm_dup_error ()
int	fpi_ssm_get_cur_state ()
void	fpi_ssm_silence_debug ()
void	fpi_ssm_spi_transfer_cb ()
void	fpi_ssm_spi_transfer_with_weak_pointer_cb ()
void	fpi_ssm_usb_transfer_cb ()
void	fpi_ssm_usb_transfer_with_weak_pointer_cb ()

Types and Values

FpiSsm

Description

Asynchronous driver design encourages some kind of state machine behind it. FpiSsm provides a simple mechanism to implement a state machine, which is often entirely linear. You can however also jump to a specific state or do an early return from the SSM by completing it.

e.g. S1 ↦ S2 ↦ S3 ↦ S4 ↦ C1 ↦ C2 ↦ final

Where S1 is the start state. The C1 and later states are cleanup states that may be defined. The difference is that these states will never be skipped when marking the SSM as completed.

Use fpi_ssm_new() to create a new state machine with a defined number of states. Note that the state numbers start at zero, making them match the first value in a C enumeration.

To start a ssm, you pass in a completion callback function to fpi_ssm_start() which gets called when the ssm completes (both on failure and on success). Starting a ssm also takes ownership of it and it will be automatically free'ed after the callback function has been called.

To iterate to the next state, call fpi_ssm_next_state(). It is legal to attempt to iterate beyond the final state - this is equivalent to marking the ssm as successfully completed.

To mark successful completion of a SSM, either iterate beyond the final state or call fpi_ssm_mark_completed() from any state.

To mark failed completion of a SSM, call fpi_ssm_mark_failed() from any state. You must pass a non-zero error code.

Your state handling function looks at the return value of fpi_ssm_get_cur_state() in order to determine the current state and hence which operations to perform (a switch statement is appropriate).

Typically, the state handling function fires off an asynchronous communication with the device (such as a USB transfer), and the callback function iterates the machine to the next state upon success (or fails).

Functions

FpiSsmCompletedCallback ()

void
(*FpiSsmCompletedCallback) (FpiSsm *ssm,
                            FpDevice *dev,
                            GError *error);

The callback called when a state machine completes successfully, as set when calling fpi_ssm_start().

Parameters

ssm	a FpiSsm state machine
dev	the fp_dev fingerprint device
error	The GError or `NULL` on successful completion.	[transfer full]

FpiSsmHandlerCallback ()

void
(*FpiSsmHandlerCallback) (FpiSsm *ssm,
                          FpDevice *dev);

The callback called when a state machine transitions from one state to the next, as set when calling fpi_ssm_new().

Parameters

ssm	a FpiSsm state machine
dev	the fp_dev fingerprint device

fpi_ssm_new()

#define             fpi_ssm_new(dev, handler, nr_states)

Allocate a new ssm, with nr_states states. The handler callback will be called after each state transition. This is a macro that calls fpi_ssm_new_full() using nr_states as the cleanup states and using the stringified version of nr_states . It should be used with an enum value.

Parameters

dev	a fp_dev fingerprint device
handler	the callback function
nr_states	the number of states

Returns

a new FpiSsm state machine

fpi_ssm_new_full ()

FpiSsm *
fpi_ssm_new_full (FpDevice *dev,
                  FpiSsmHandlerCallback handler,
                  int nr_states,
                  int start_cleanup,
                  const char *machine_name);

Allocate a new ssm, with nr_states states. The handler callback will be called after each state transition.

Parameters

dev	a fp_dev fingerprint device
handler	the callback function
nr_states	the number of states
start_cleanup	the first cleanup state
machine_name	the name of the state machine (for debug purposes)

Returns

a new FpiSsm state machine

fpi_ssm_free ()

void
fpi_ssm_free (FpiSsm *machine);

Frees a state machine. This does not call any error or success callbacks, so you need to do this yourself.

Parameters

machine

an FpiSsm state machine

fpi_ssm_start ()

void
fpi_ssm_start (FpiSsm *ssm,
               FpiSsmCompletedCallback callback);

Starts a state machine. You can also use this function to restart a completed or failed state machine. The callback will be called on completion.

Note that ssm will be stolen when this function is called. So that all associated data will be free'ed automatically, after the callback is ran.

Parameters

ssm	an FpiSsm state machine.	[transfer full]
callback	the FpiSsmCompletedCallback callback to call on completion

fpi_ssm_start_subsm ()

void
fpi_ssm_start_subsm (FpiSsm *parent,
                     FpiSsm *child);

Starts a state machine as a child of another. if the child completes successfully, the parent will be advanced to the next state. if the child fails, the parent will be marked as failed with the same error code.

The child will be automatically freed upon completion or failure.

Parameters

parent	an FpiSsm state machine
child	an FpiSsm state machine

fpi_ssm_next_state ()

void
fpi_ssm_next_state (FpiSsm *machine);

Iterate to next state of a state machine. If the current state is the last state, then the state machine will be marked as completed, as if calling fpi_ssm_mark_completed().

Parameters

machine

an FpiSsm state machine

fpi_ssm_next_state_delayed ()

void
fpi_ssm_next_state_delayed (FpiSsm *machine,
                            int delay);

Iterate to next state of a state machine with a delay of delay ms. If the current state is the last state, then the state machine will be marked as completed, as if calling fpi_ssm_mark_completed().

Parameters

machine	an FpiSsm state machine
delay	the milliseconds to wait before switching to the next state

fpi_ssm_jump_to_state ()

void
fpi_ssm_jump_to_state (FpiSsm *machine,
                       int state);

Jump to the state state, bypassing intermediary states. If state is the last state, the machine won't be completed unless fpi_ssm_mark_completed() isn't explicitly called.

Parameters

machine	an FpiSsm state machine
state	the state to jump to

fpi_ssm_jump_to_state_delayed ()

void
fpi_ssm_jump_to_state_delayed (FpiSsm *machine,
                               int state,
                               int delay);

Jump to the state state with a delay of delay milliseconds, bypassing intermediary states.

Parameters

machine	an FpiSsm state machine
state	the state to jump to
delay	the milliseconds to wait before switching to `state` state

fpi_ssm_cancel_delayed_state_change ()

void
fpi_ssm_cancel_delayed_state_change (FpiSsm *machine);

fpi_ssm_mark_completed ()

void
fpi_ssm_mark_completed (FpiSsm *machine);

Mark a ssm as completed successfully. The callback set when creating the state machine with fpi_ssm_new() will be called synchronously.

Note that any later cleanup state will still be executed.

Parameters

machine

an FpiSsm state machine

fpi_ssm_mark_failed ()

void
fpi_ssm_mark_failed (FpiSsm *machine,
                     GError *error);

Mark a state machine as failed with error as the error code, completing it.

Parameters

machine	an FpiSsm state machine
error	a GError.	[transfer full]

fpi_ssm_set_data ()

void
fpi_ssm_set_data (FpiSsm *machine,
                  gpointer ssm_data,
                  GDestroyNotify ssm_data_destroy);

Sets machine 's data (freeing the existing data, if any).

Parameters

machine	an FpiSsm state machine
ssm_data	a pointer to machine data.	[nullable]
ssm_data_destroy	GDestroyNotify for `ssm_data` .	[nullable]

fpi_ssm_get_data ()

gpointer
fpi_ssm_get_data (FpiSsm *machine);

Retrieve the pointer to SSM data set with fpi_ssm_set_ssm_data()

Parameters

machine

an FpiSsm state machine

Returns

a pointer

fpi_ssm_get_device ()

FpDevice *
fpi_ssm_get_device (FpiSsm *machine);

Retrieve the device that the SSM is for.

Parameters

machine

an FpiSsm state machine

Returns

FpDevice

fpi_ssm_get_error ()

GError *
fpi_ssm_get_error (FpiSsm *machine);

Returns the error code set by fpi_ssm_mark_failed().

fpi_ssm_spi_transfer_cb ()

void
fpi_ssm_spi_transfer_cb (FpiSpiTransfer *transfer,
                         FpDevice *device,
                         gpointer unused_data,
                         GError *error);

Can be used in as a FpiSpiTransfer callback handler to automatically advance or fail a statemachine on transfer completion.

Make sure to set the FpiSsm on the transfer.

Parameters

transfer	a FpiSpiTransfer
device	a FpDevice
unused_data	User data (unused)
error	The GError or `NULL`

fpi_ssm_spi_transfer_with_weak_pointer_cb ()

void
fpi_ssm_spi_transfer_with_weak_pointer_cb
                               (FpiSpiTransfer *transfer,
                                FpDevice *device,
                                gpointer weak_ptr,
                                GError *error);

Can be used in as a FpiSpiTransfer callback handler to automatically advance or fail a statemachine on transfer completion. Passing a gpointer* as weak_ptr permits to nullify it once we're done with the transfer.

Make sure to set the FpiSsm on the transfer.

Parameters

transfer	a FpiSpiTransfer
device	a FpDevice
weak_ptr	A gpointer pointer to nullify. You can pass a pointer to any gpointer to nullify when the callback is completed. I.e a pointer to the current FpiSpiTransfer.
error	The GError or `NULL`

fpi_ssm_usb_transfer_cb ()

void
fpi_ssm_usb_transfer_cb (FpiUsbTransfer *transfer,
                         FpDevice *device,
                         gpointer unused_data,
                         GError *error);

Can be used in as a FpiUsbTransfer callback handler to automatically advance or fail a statemachine on transfer completion.

Make sure to set the FpiSsm on the transfer.

Parameters

transfer	a FpiUsbTransfer
device	a FpDevice
unused_data	User data (unused)
error	The GError or `NULL`

fpi_ssm_usb_transfer_with_weak_pointer_cb ()

void
fpi_ssm_usb_transfer_with_weak_pointer_cb
                               (FpiUsbTransfer *transfer,
                                FpDevice *device,
                                gpointer weak_ptr,
                                GError *error);

Can be used in as a FpiUsbTransfer callback handler to automatically advance or fail a statemachine on transfer completion. Passing a gpointer* as weak_ptr permits to nullify it once we're done with the transfer.

Make sure to set the FpiSsm on the transfer.

Parameters

transfer	a FpiUsbTransfer
device	a FpDevice
weak_ptr	A gpointer pointer to nullify. You can pass a pointer to any gpointer to nullify when the callback is completed. I.e a pointer to the current FpiUsbTransfer.
error	The GError or `NULL`

Types and Values

FpiSsm

typedef struct _FpiSsm FpiSsm;

Sequential state machine that iterates sequentially over a predefined series of states. Can be terminated by either completion or failure error conditions.