HEARTBEAT API

Introduction:

1. ll_cluster_new()
2. singon()
3. signoff()
4. delete()
5. set_msg_callback()
6. set_nstatus_callback()
7. set _ifstatus_callback()
8. init_nodewalk()
9. nextnode()
10. end_nodewalk()
11. init_ifwalk()
12. nextif()
13. end_ifwalk()
14. if_status()
15. sendclustermsg()
16. sendnodemsg()
17. inputfd()
18. msgready()
19. setmsgsignal()
20. rcvmsg()
21. readmsg()
22. setfmode()
23. errmsg()

Description:

ll_cluster_new()

Parameter description:

'type' identifies the service provider. It's value must currently be "heartbeat".

Description:

Register with the heartbeat library and create a client instance of type "heartbeat"

Return Value:

returns a handle to the heartbeat library instance. This handle is a opaque object with a set of member functions. The member functions provide the necessary mechanism to interact with the heartbeat daemon. Returns NULL on failure.

Observation:

Why is 'type' parameter required when we know for sure that we are only interacting with the heartbeat daemon? Or is it that the library wants to be generic and wants to interact with any arbitrary daemon? Yes.  The latter.

signon()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new() 'service' is the type of service, which the calling process registers with the heartbeat daemon.

Description:

This function sets up a communication link with the local heartbeat daemon and registers itself for the 'service' service. In the case of casual client the clientid is NULL. But in the case of non-casual client the clientid is non-NULL and it indicates the service to which this client wants to sign on for. This special communication link setup with the heartbeat daemon is a fifo. Non-casual clients interact using a fifo whose name is derived from the pid of the clients process. Casual clients interact with heartbeat daemon using the fifo whose name is derived from the 'service'string.

The heartbeat daemon has no notion for 'service'. Only the clients registered with the heartbeat daemons for the same service, have the notion for that service.  'service' mostly is a mechanism of providing primitive group services to a set of non-casual clients registered for that service.

Return value:

On success returns HA_OK
On failure returns HA_FAIL

signoff()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new()

Description:

This function deletes the communication link with the local heartbeat daemon and unsubscribe itself from being a heartbeat client.

Return Value:

On success it returns HA_OK.
On failure it returns HA_FAIL.

delete()

Parameter Description:

cinfo'

is the handle to the library instance got through ll_cluster_new()

Description:

This operation is reverse of ll_cluster_new(). It unsubscribes itself from the heartbeat library and cleans up the corresponding datastructures.

Return Value:

On success returns HA_OK
On failure returns HA_FAIL

set_msg_callback()

Parameter Description:

cinfo'

is the handle to the library instance got through ll_cluster_new()

'msgtype'

is the type of message on receipt of which the 'callback' is called.

'callback'

is the function to be called on receipt of a message of type 'msgtype'.

'p'

is the parameter to be passed to the 'callback' function.

Description:

This function registers a callback function along with its parameter. The callback function is called by the heartbeat library on receipt of a message of type 'msgtype' from the heartbeat daemon.

NOTE:

Neither the heartbeat library nor heartbeat daemon interpret 'msgtype'. The 'msgtype' is interpreted only by the client.  Clients can coin their own msgtype as long as all the clients signed up for the same service can interpret it.

Return Value:

On success HA_OK is returned.
On failure HA_FAIL is returned.

set_nstatus_callback()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new

'cbf'

is the function pointer to be called on change of status of any node in the cluster.

'p'

is the parameter to be passed to the callback function.

Description:

This function registers a callback function along with its parameter. The callback function is called by the heartbeat library on change of status of any node in the cluster.

Return Value:

On success HA_OK is returned.

Observation:

There is a bug in this function. It does not validate the 'cinfo' parameter'. It should return HA_FAIL on failure.

set_ifstatus_callback()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new()

cbf'

is the function pointer to be called on change of status of any interface in the cluster.

'p'

is the parameter to be passed for the callback function.

Description:

This function registers a callback function along with its parameter. The callback function is called by the heartbeat library on change of status of any network interface in the cluster in the view of the current cluster node.

Return Value:

On success HA_OK is returned.

Also there is a bug in this function. It does not validate the 'cinfo' parameter'. It should return HA_FAIL on failure.

init_nodewalk()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new

Description:

This function talks to the heartbeat daemon and retrieves the set of nodes that are part of the cluster. If the retrieval is successful HA_OK is returned.

Return Value:

On success HA_OK is returned
On failure HA_FAIL is returned

nextnode()

Parameter Description:

'cinfo'

is the handle to the library instance gotten through ll_cluster_new().

Description/Return Value:,

This function returns the next node in the cluster, which is cached in the heartbeat library. If no more node is available it returns NULL.

end_nodewalk()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

Description:

This clears the cluster node information cached in the heartbeat library.

Return Value:

returns HA_OK on success  and HA_FAIL on failure.

init_ifwalk()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new

'host'

is the node in the cluster whose network interfaces are of interest.

Description:

This function talks to the heartbeat daemon and caches all the network interface information associated with 'host' node. This caching is done in the heartbeat library.

Return Value:

If the network interface information can be successfully retrieved, HA_OK is returned. Failure returns HA_FAIL.

nextif()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

Description:

This function returns the next network interface of the 'host' node in the cluster, which is cached in the heartbeat library.

NOTE:

The 'host' is the node of the cluster specified during the call to init_ifwalk()

Return Value:

If no more interfaces are available it returns NULL.

end_ifwalk()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

Description:

This clears the network interface information cached in the heartbeat library.

Return Value:

returns HA_OK on success and HA_FAIL of failure.

if_status()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'host'

is the node name whose interface's status is queried.

'ifname'

is the name of the interface whose status is queried.

Description:

This function returns a string that specifies the state of the interface 'ifname' on cluster node 'host'

Return Value:

It returns "up" if the link is active and "dead" if the link is down. NULL if there was a error.

sendclustermsg()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'msg'

is the message to be sent to all non-casual clients signed up for the same service as that of the calling client.

Description:

This function broadcasts the message to all members of the group.

Return Value:

This function returns HA_FAIL if called by a casual client or if there was some other failure.
On success it returns HA_OK.

sendnodemsg()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'msg'

is the message to be sent to a non-casual client signed on to the same service on node 'nodename'.

Description:

This function sends the message to a non-casual client residing on node 'nodename'. The client belongs to the same group as that of the calling client.

Return Value:

This function returns HA_FAIL if called by a casual client or if there was some other failure.
On success it returns HA_OK.

inputfd()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

Description/Return Value:

returns the file descriptor of the communication link setup with the local heartbeat daemon.
On failure it returns -1.

Observation:

This function is needed in order to be able to perform a select function which selects on incoming API messages. It should not be used for any other purpose.

msgready()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

Description:

checks if there is any message to be read.

Return Value:

If a message is ready to be read returns non zero value. Otherwise returns 0.

setmsgsignal()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'nsig'

is the signal to be used by heartbeat daemon to signal the client process.

Description:

This function informs the heartbeat daemon send signal number 'nsig' whenever a message arrives for it.

Return Value:

returns HA_OK on success
and HA_FAIL on failure

rcvmsg()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'blocking'

indicates whether to block for the receipt of a message or not.

Description/Return Value:

This function returns true if a message for which a callback function was not registered is received.

If blocking is set, then it waits till a message arrives. But it returns true only if that message does not have a callback registered.

NOTE:

In all cases, received messages are deleted by this call.

Observation:

This interface is provided as a convenience to allow for clients which only process certain message types through registered callback functions to never have to worry about the possibility of failing to destroy their messages. If you process all messages you handle with callbacks, then this function is a convenient choice. Otherwise, you likely need to use readmsg().

readmsg()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'blocking'

indicates whether to block for the receipt of a message or not.

Description/Return Value:

This function is same as rcvmsg except that it returns messages without registered callbacks to the caller (and does not delete them). It returns the next message for which a callback is not registered.

If 'blocking' is set to FALSE, it will not wait for a message to arrive. It returns NULL if there is not currently a message ready to read which is not intercepted by a callback function.

NOTE:

The message returned must be disposed off by the caller by calling ha_msg_del().

setfmode()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new().

'mode'

indicates the type of messages to be delivered to the client and to filter out the rest.

The modes have the following meanings:

LLC_FILTER_DEFAULT

All messages destined to this client are received, along with all that are addressed to all clients.

LLC_FILTER_PMODE

All messages, but filter out heartbeats that don't tell us anything new.

LLC_FILTER_ALLHB

All heartbeats including those that don't change status.

LLC_FILTER_RAW

All packets from all interfaces, even duplicates. Packets with authentication errors are still ignored.

Description:

This function sets up the type of messages that the client is interested; to be received from the local heartbeat daemon. It is mainly used for debugging.

Return Value:

returns HA_OK on success and HA_FAIL on failure

errmsg()

Parameter Description:

'cinfo'

is the handle to the library instance got through ll_cluster_new

Description/Return Value:

This function returns the last set of error messages from the previous API call. This is not a very wonderful interface (according to alanr)