[asterisk/asterisk.git] / main / ccss.c

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2010, Digium, Inc.
 *
 * Mark Michelson <mmichelson@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 * \brief Call Completion Supplementary Services implementation
 * \author Mark Michelson <mmichelson@digium.com>
 */

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision$")

#include "asterisk/astobj2.h"
#include "asterisk/strings.h"
#include "asterisk/ccss.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/utils.h"
#include "asterisk/taskprocessor.h"
#include "asterisk/event.h"
#include "asterisk/devicestate.h"
#include "asterisk/module.h"
#include "asterisk/app.h"
#include "asterisk/cli.h"
#include "asterisk/manager.h"
#include "asterisk/causes.h"

/*** DOCUMENTATION
        <application name="CallCompletionRequest" language="en_US">
                <synopsis>
                        Request call completion service for previous call
                </synopsis>
                <syntax />
                <description>
                        <para>Request call completion service for a previously failed
                        call attempt.</para>
                        <para>This application sets the following channel variables:</para>
                        <variablelist>
                                <variable name="CC_REQUEST_RESULT">
                                        <para>This is the returned status of the request.</para>
                                        <value name="SUCCESS" />
                                        <value name="FAIL" />
                                </variable>
                                <variable name="CC_REQUEST_REASON">
                                        <para>This is the reason the request failed.</para>
                                        <value name="NO_CORE_INSTANCE" />
                                        <value name="NOT_GENERIC" />
                                        <value name="TOO_MANY_REQUESTS" />
                                        <value name="UNSPECIFIED" />
                                </variable>
                        </variablelist>
                </description>
        </application>
        <application name="CallCompletionCancel" language="en_US">
                <synopsis>
                        Cancel call completion service
                </synopsis>
                <syntax />
                <description>
                        <para>Cancel a Call Completion Request.</para>
                        <para>This application sets the following channel variables:</para>
                        <variablelist>
                                <variable name="CC_CANCEL_RESULT">
                                        <para>This is the returned status of the cancel.</para>
                                        <value name="SUCCESS" />
                                        <value name="FAIL" />
                                </variable>
                                <variable name="CC_CANCEL_REASON">
                                        <para>This is the reason the cancel failed.</para>
                                        <value name="NO_CORE_INSTANCE" />
                                        <value name="NOT_GENERIC" />
                                        <value name="UNSPECIFIED" />
                                </variable>
                        </variablelist>
                </description>
        </application>
 ***/

/* These are some file-scoped variables. It would be
 * nice to define them closer to their first usage, but since
 * they are used in many places throughout the file, defining
 * them here at the top is easiest.
 */

/*!
 * The ast_sched_context used for all generic CC timeouts
 */
static struct ast_sched_context *cc_sched_context;
/*!
 * Counter used to create core IDs for CC calls. Each new
 * core ID is created by atomically adding 1 to the core_id_counter
 */
static int core_id_counter;
/*!
 * Taskprocessor from which all CC agent and monitor callbacks
 * are called.
 */
static struct ast_taskprocessor *cc_core_taskprocessor;
/*!
 * Name printed on all CC log messages.
 */
static const char *CC_LOGGER_LEVEL_NAME = "CC";
/*!
 * Logger level registered by the CC core.
 */
static int cc_logger_level;
/*!
 * Parsed configuration value for cc_max_requests
 */
static unsigned int global_cc_max_requests;
/*!
 * The current number of CC requests in the system
 */
static int cc_request_count;

static inline void *cc_ref(void *obj, const char *debug)
{
        ao2_t_ref(obj, +1, debug);
        return obj;
}

static inline void *cc_unref(void *obj, const char *debug)
{
        ao2_t_ref(obj, -1, debug);
        return NULL;
}

/*!
 * \since 1.8
 * \internal
 * \brief A structure for holding the configuration parameters
 * relating to CCSS
 */
struct ast_cc_config_params {
        enum ast_cc_agent_policies cc_agent_policy;
        enum ast_cc_monitor_policies cc_monitor_policy;
        unsigned int cc_offer_timer;
        unsigned int ccnr_available_timer;
        unsigned int ccbs_available_timer;
        unsigned int cc_recall_timer;
        unsigned int cc_max_agents;
        unsigned int cc_max_monitors;
        char cc_callback_macro[AST_MAX_EXTENSION];
        char cc_agent_dialstring[AST_MAX_EXTENSION];
};

/*!
 * \since 1.8
 * \brief The states used in the CCSS core state machine
 *
 * For more information, see doc/CCSS_architecture.pdf
 */
enum cc_state {
        /*! Entered when it is determined that CCSS may be used for the call */
        CC_AVAILABLE,
        /*! Entered when a CCSS agent has offered CCSS to a caller */
        CC_CALLER_OFFERED,
        /*! Entered when a CCSS agent confirms that a caller has
         * requested CCSS */
        CC_CALLER_REQUESTED,
        /*! Entered when a CCSS monitor confirms acknowledgment of an
         * outbound CCSS request */
        CC_ACTIVE,
        /*! Entered when a CCSS monitor alerts the core that the called party
         * has become available */
        CC_CALLEE_READY,
        /*! Entered when a CCSS agent alerts the core that the calling party
         * may not be recalled because he is unavailable
         */
        CC_CALLER_BUSY,
        /*! Entered when a CCSS agent alerts the core that the calling party
         * is attempting to recall the called party
         */
        CC_RECALLING,
        /*! Entered when an application alerts the core that the calling party's
         * recall attempt has had a call progress response indicated
         */
        CC_COMPLETE,
        /*! Entered any time that something goes wrong during the process, thus
         * resulting in the failure of the attempted CCSS transaction. Note also
         * that cancellations of CC are treated as failures.
         */
        CC_FAILED,
};

/*!
 * \brief The payload for an AST_CONTROL_CC frame
 *
 * \details
 * This contains all the necessary data regarding
 * a called device so that the CC core will be able
 * to allocate the proper monitoring resources.
 */
struct cc_control_payload {
        /*!
         * \brief The type of monitor to allocate.
         *
         * \details
         * The type of monitor to allocate. This is a string which corresponds
         * to a set of monitor callbacks registered. Examples include "generic"
         * and "SIP"
         *
         * \note This really should be an array of characters in case this payload
         * is sent accross an IAX2 link.  However, this would not make too much sense
         * given this type may not be recognized by the other end.
         * Protection may be necessary to prevent it from being transmitted.
         *
         * In addition the following other problems are also possible:
         * 1) Endian issues with the integers/enums stored in the config_params.
         * 2) Alignment padding issues for the element types.
         */
        const char *monitor_type;
        /*!
         * \brief Private data allocated by the callee
         *
         * \details
         * All channel drivers that monitor endpoints will need to allocate
         * data that is not usable by the CC core. In most cases, some or all
         * of this data is allocated at the time that the channel driver offers
         * CC to the caller. There are many opportunities for failures to occur
         * between when a channel driver offers CC and when a monitor is actually
         * allocated to watch the endpoint. For this reason, the channel driver
         * must give the core a pointer to the private data that was allocated so
         * that the core can call back into the channel driver to destroy it if
         * a failure occurs. If no private data has been allocated at the time that
         * CC is offered, then it is perfectly acceptable to pass NULL for this
         * field.
         */
        void *private_data;
        /*!
         * \brief Service offered by the endpoint
         *
         * \details
         * This indicates the type of call completion service offered by the
         * endpoint. This data is not crucial to the machinations of the CC core,
         * but it is helpful for debugging purposes.
         */
        enum ast_cc_service_type service;
        /*!
         * \brief Configuration parameters used by this endpoint
         *
         * \details
         * Each time an endpoint offers call completion, it must provide its call
         * completion configuration parameters. This is because settings may be different
         * depending on the circumstances.
         */
        struct ast_cc_config_params config_params;
        /*!
         * \brief ID of parent extension
         *
         * \details
         * This is the only datum that the CC core derives on its own and is not
         * provided by the offerer of CC. This provides the core with information on
         * which extension monitor is the most immediate parent of this device.
         */
        int parent_interface_id;
        /*!
         * \brief Name of device to be monitored
         *
         * \details
         * The device name by which this monitored endpoint will be referred in the
         * CC core. It is highly recommended that this device name is derived by using
         * the function ast_channel_get_device_name.
         */
        char device_name[AST_CHANNEL_NAME];
        /*!
         * \brief Recall dialstring
         *
         * \details
         * Certain channel drivers (DAHDI in particular) will require that a special
         * dialstring be used to indicate that the outgoing call is to interpreted as
         * a CC recall. If the channel driver has such a requirement, then this is
         * where that special recall dialstring is placed. If no special dialstring
         * is to be used, then the channel driver must provide the original dialstring
         * used to call this endpoint.
         */
        char dialstring[AST_CHANNEL_NAME];
};

/*!
 * \brief The "tree" of interfaces that is dialed.
 *
 * \details
 * Though this is a linked list, it is logically treated
 * as a tree of monitors. Each monitor has an id and a parent_id
 * associated with it. The id is a unique ID for that monitor, and
 * the parent_id is the unique ID of the monitor's parent in the
 * tree. The tree is structured such that all of a parent's children
 * will appear after the parent in the tree. However, it cannot be
 * guaranteed exactly where after the parent the children are.
 *
 * The tree is reference counted since several threads may need
 * to use it, and it may last beyond the lifetime of a single
 * thread.
 */
AST_LIST_HEAD(cc_monitor_tree, ast_cc_monitor);

static const int CC_CORE_INSTANCES_BUCKETS = 17;
static struct ao2_container *cc_core_instances;

struct cc_core_instance {
        /*!
         * Unique identifier for this instance of the CC core.
         */
        int core_id;
        /*!
         * The current state for this instance of the CC core.
         */
        enum cc_state current_state;
        /*!
         * The CC agent in use for this call
         */
        struct ast_cc_agent *agent;
        /*!
         * Reference to the monitor tree formed during the initial call
         */
        struct cc_monitor_tree *monitors;
};

/*!
 * \internal
 * \brief Request that the core change states
 * \param state The state to which we wish to change
 * \param core_id The unique identifier for this instance of the CCSS core state machine
 * \param debug Optional message explaining the reason for the state change
 * \param ap varargs list
 * \retval 0 State change successfully queued
 * \retval -1 Unable to queue state change request
 */
static int __attribute__((format(printf, 3, 0))) cc_request_state_change(enum cc_state state, const int core_id, const char *debug, va_list ap);

/*!
 * \internal
 * \brief create a new instance of the CC core and an agent for the calling channel
 *
 * This function will check to make sure that the incoming channel
 * is allowed to request CC by making sure that the incoming channel
 * has not exceeded its maximum number of allowed agents.
 *
 * Should that check pass, the core instance is created, and then the
 * agent for the channel.
 *
 * \param caller_chan The incoming channel for this particular call
 * \param called_tree A reference to the tree of called devices. The agent
 * will gain a reference to this tree as well
 * \param core_id The core_id that this core_instance will assume
 * \retval NULL Failed to create the core instance either due to memory allocation
 * errors or due to the agent count for the caller being too high
 * \retval non-NULL A reference to the newly created cc_core_instance
 */
static struct cc_core_instance *cc_core_init_instance(struct ast_channel *caller_chan,
                struct cc_monitor_tree *called_tree, const int core_id, struct cc_control_payload *cc_data);

static const struct {
        enum ast_cc_service_type service;
        const char *service_string;
} cc_service_to_string_map[] = {
        {AST_CC_NONE, "NONE"},
        {AST_CC_CCBS, "CCBS"},
        {AST_CC_CCNR, "CCNR"},
        {AST_CC_CCNL, "CCNL"},
};

static const struct {
        enum cc_state state;
        const char *state_string;
} cc_state_to_string_map[] = {
        {CC_AVAILABLE,          "CC is available"},
        {CC_CALLER_OFFERED,     "CC offered to caller"},
        {CC_CALLER_REQUESTED,   "CC requested by caller"},
        {CC_ACTIVE,             "CC accepted by callee"},
        {CC_CALLEE_READY,       "Callee has become available"},
        {CC_CALLER_BUSY,        "Callee was ready, but caller is now unavailable"},
        {CC_RECALLING,          "Caller is attempting to recall"},
        {CC_COMPLETE,           "Recall complete"},
        {CC_FAILED,             "CC has failed"},
};

static const char *cc_state_to_string(enum cc_state state)
{
        return cc_state_to_string_map[state].state_string;
}

static const char *cc_service_to_string(enum ast_cc_service_type service)
{
        return cc_service_to_string_map[service].service_string;
}

static int cc_core_instance_hash_fn(const void *obj, const int flags)
{
        const struct cc_core_instance *core_instance = obj;
        return core_instance->core_id;
}

static int cc_core_instance_cmp_fn(void *obj, void *arg, int flags)
{
        struct cc_core_instance *core_instance1 = obj;
        struct cc_core_instance *core_instance2 = arg;

        return core_instance1->core_id == core_instance2->core_id ? CMP_MATCH | CMP_STOP : 0;
}

static struct cc_core_instance *find_cc_core_instance(const int core_id)
{
        struct cc_core_instance finder = {.core_id = core_id,};

        return ao2_t_find(cc_core_instances, &finder, OBJ_POINTER, "Finding a core_instance");
}

struct cc_callback_helper {
        ao2_callback_fn *function;
        void *args;
        const char *type;
};

static int cc_agent_callback_helper(void *obj, void *args, int flags)
{
        struct cc_core_instance *core_instance = obj;
        struct cc_callback_helper *helper = args;

        if (strcmp(core_instance->agent->callbacks->type, helper->type)) {
                return 0;
        }

        return helper->function(core_instance->agent, helper->args, flags);
}

struct ast_cc_agent *ast_cc_agent_callback(int flags, ao2_callback_fn *function, void *args, const char * const type)
{
        struct cc_callback_helper helper = {.function = function, .args = args, .type = type};
        struct cc_core_instance *core_instance;
        if ((core_instance = ao2_t_callback(cc_core_instances, flags, cc_agent_callback_helper, &helper,
                                        "Calling provided agent callback function"))) {
                struct ast_cc_agent *agent = cc_ref(core_instance->agent, "An outside entity needs the agent");
                cc_unref(core_instance, "agent callback done with the core_instance");
                return agent;
        }
        return NULL;
}

enum match_flags {
        /* Only match agents that have not yet
         * made a CC request
         */
        MATCH_NO_REQUEST = (1 << 0),
        /* Only match agents that have made
         * a CC request
         */
        MATCH_REQUEST = (1 << 1),
};

/* ao2_callbacks for cc_core_instances */

/*!
 * \internal
 * \brief find a core instance based on its agent
 *
 * The match flags tell whether we wish to find core instances
 * that have a monitor or core instances that do not. Core instances
 * with no monitor are core instances for which a caller has not yet
 * requested CC. Core instances with a monitor are ones for which the
 * caller has requested CC.
 */
static int match_agent(void *obj, void *arg, void *data, int flags)
{
        struct cc_core_instance *core_instance = obj;
        const char *name = arg;
        unsigned long match_flags = *(unsigned long *)data;
        int possible_match = 0;

        if ((match_flags & MATCH_NO_REQUEST) && core_instance->current_state < CC_CALLER_REQUESTED) {
                possible_match = 1;
        }

        if ((match_flags & MATCH_REQUEST) && core_instance->current_state >= CC_CALLER_REQUESTED) {
                possible_match = 1;
        }

        if (!possible_match) {
                return 0;
        }

        if (!strcmp(core_instance->agent->device_name, name)) {
                return CMP_MATCH | CMP_STOP;
        }
        return 0;
}

struct count_agents_cb_data {
        int count;
        int core_id_exception;
};

/*!
 * \internal
 * \brief Count the number of agents a specific interface is using
 *
 * We're only concerned with the number of agents that have requested
 * CC, so we restrict our search to core instances which have a non-NULL
 * monitor pointer
 */
static int count_agents_cb(void *obj, void *arg, void *data, int flags)
{
        struct cc_core_instance *core_instance = obj;
        const char *name = arg;
        struct count_agents_cb_data *cb_data = data;

        if (cb_data->core_id_exception == core_instance->core_id) {
                ast_log_dynamic_level(cc_logger_level, "Found agent with core_id %d but not counting it toward total\n", core_instance->core_id);
                return 0;
        }

        if (core_instance->current_state >= CC_CALLER_REQUESTED && !strcmp(core_instance->agent->device_name, name)) {
                cb_data->count++;
        }
        return 0;
}

/* default values mapping from cc_state to ast_dev_state */

#define CC_AVAILABLE_DEVSTATE_DEFAULT        AST_DEVICE_NOT_INUSE
#define CC_CALLER_OFFERED_DEVSTATE_DEFAULT   AST_DEVICE_NOT_INUSE
#define CC_CALLER_REQUESTED_DEVSTATE_DEFAULT AST_DEVICE_NOT_INUSE
#define CC_ACTIVE_DEVSTATE_DEFAULT           AST_DEVICE_INUSE
#define CC_CALLEE_READY_DEVSTATE_DEFAULT     AST_DEVICE_RINGING
#define CC_CALLER_BUSY_DEVSTATE_DEFAULT      AST_DEVICE_ONHOLD
#define CC_RECALLING_DEVSTATE_DEFAULT        AST_DEVICE_RINGING
#define CC_COMPLETE_DEVSTATE_DEFAULT         AST_DEVICE_NOT_INUSE
#define CC_FAILED_DEVSTATE_DEFAULT           AST_DEVICE_NOT_INUSE

/*!
 * \internal
 * \brief initialization of defaults for CC_STATE to DEVICE_STATE map
 */
static enum ast_device_state cc_state_to_devstate_map[] = {
        [CC_AVAILABLE] =        CC_AVAILABLE_DEVSTATE_DEFAULT,
        [CC_CALLER_OFFERED] =   CC_CALLER_OFFERED_DEVSTATE_DEFAULT,
        [CC_CALLER_REQUESTED] = CC_CALLER_REQUESTED_DEVSTATE_DEFAULT,
        [CC_ACTIVE] =           CC_ACTIVE_DEVSTATE_DEFAULT,
        [CC_CALLEE_READY] =     CC_CALLEE_READY_DEVSTATE_DEFAULT,
        [CC_CALLER_BUSY] =      CC_CALLER_BUSY_DEVSTATE_DEFAULT,
        [CC_RECALLING] =        CC_RECALLING_DEVSTATE_DEFAULT,
        [CC_COMPLETE] =         CC_COMPLETE_DEVSTATE_DEFAULT,
        [CC_FAILED] =           CC_FAILED_DEVSTATE_DEFAULT,
};

/*!
 * \intenral
 * \brief lookup the ast_device_state mapped to cc_state
 *
 * \return the correponding DEVICE STATE from the cc_state_to_devstate_map
 * when passed an internal state.
 */
static enum ast_device_state cc_state_to_devstate(enum cc_state state)
{
        return cc_state_to_devstate_map[state];
}

/*!
 * \internal
 * \brief Callback for devicestate providers
 *
 * \details
 * Initialize with ast_devstate_prov_add() and returns the corresponding
 * DEVICE STATE based on the current CC_STATE state machine if the requested
 * device is found and is a generic device. Returns the equivalent of
 * CC_FAILED, which defaults to NOT_INUSE, if no device is found.  NOT_INUSE would
 * indicate that there is no presence of any pending call back.
 */
static enum ast_device_state ccss_device_state(const char *device_name)
{
        struct cc_core_instance *core_instance;
        unsigned long match_flags;
        enum ast_device_state cc_current_state;

        match_flags = MATCH_NO_REQUEST;
        core_instance = ao2_t_callback_data(cc_core_instances, 0, match_agent,
                (char *) device_name, &match_flags,
                "Find Core Instance for ccss_device_state reqeust.");
        if (!core_instance) {
                ast_log_dynamic_level(cc_logger_level,
                        "Couldn't find a core instance for caller %s\n", device_name);
                return cc_state_to_devstate(CC_FAILED);
        }

        ast_log_dynamic_level(cc_logger_level,
                "Core %d: Found core_instance for caller %s in state %s\n",
                core_instance->core_id, device_name, cc_state_to_string(core_instance->current_state));

        if (strcmp(core_instance->agent->callbacks->type, "generic")) {
                ast_log_dynamic_level(cc_logger_level,
                        "Core %d: Device State is only for generic agent types.\n",
                        core_instance->core_id);
                cc_unref(core_instance, "Unref core_instance since ccss_device_state was called with native agent");
                return cc_state_to_devstate(CC_FAILED);
        }
        cc_current_state = cc_state_to_devstate(core_instance->current_state);
        cc_unref(core_instance, "Unref core_instance done with ccss_device_state");
        return cc_current_state;
}

/*!
 * \internal
 * \brief Notify Device State Changes from CC STATE MACHINE
 *
 * \details
 * Any time a state is changed, we call this function to notify the DEVICE STATE
 * subsystem of the change so that subscribed phones to any corresponding hints that
 * are using that state are updated.
 */
static void ccss_notify_device_state_change(const char *device, enum cc_state state)
{
        enum ast_device_state devstate;

        devstate = cc_state_to_devstate(state);

        ast_log_dynamic_level(cc_logger_level,
                "Notification of CCSS state change to '%s', device state '%s' for device '%s'\n",
                cc_state_to_string(state), ast_devstate2str(devstate), device);

        ast_devstate_changed(devstate, "ccss:%s", device);
}

#define CC_OFFER_TIMER_DEFAULT                  20              /* Seconds */
#define CCNR_AVAILABLE_TIMER_DEFAULT    7200    /* Seconds */
#define CCBS_AVAILABLE_TIMER_DEFAULT    4800    /* Seconds */
#define CC_RECALL_TIMER_DEFAULT                 20              /* Seconds */
#define CC_MAX_AGENTS_DEFAULT                   5
#define CC_MAX_MONITORS_DEFAULT                 5
#define GLOBAL_CC_MAX_REQUESTS_DEFAULT  20

static const struct ast_cc_config_params cc_default_params = {
        .cc_agent_policy = AST_CC_AGENT_NEVER,
        .cc_monitor_policy = AST_CC_MONITOR_NEVER,
        .cc_offer_timer = CC_OFFER_TIMER_DEFAULT,
        .ccnr_available_timer = CCNR_AVAILABLE_TIMER_DEFAULT,
        .ccbs_available_timer = CCBS_AVAILABLE_TIMER_DEFAULT,
        .cc_recall_timer = CC_RECALL_TIMER_DEFAULT,
        .cc_max_agents = CC_MAX_AGENTS_DEFAULT,
        .cc_max_monitors = CC_MAX_MONITORS_DEFAULT,
        .cc_callback_macro = "",
        .cc_agent_dialstring = "",
};

void ast_cc_default_config_params(struct ast_cc_config_params *params)
{
        *params = cc_default_params;
}

struct ast_cc_config_params *__ast_cc_config_params_init(const char *file, int line, const char *function)
{
#if defined(__AST_DEBUG_MALLOC)
        struct ast_cc_config_params *params = __ast_malloc(sizeof(*params), file, line, function);
#else
        struct ast_cc_config_params *params = ast_malloc(sizeof(*params));
#endif

        if (!params) {
                return NULL;
        }

        ast_cc_default_config_params(params);
        return params;
}

void ast_cc_config_params_destroy(struct ast_cc_config_params *params)
{
        ast_free(params);
}

static enum ast_cc_agent_policies str_to_agent_policy(const char * const value)
{
        if (!strcasecmp(value, "never")) {
                return AST_CC_AGENT_NEVER;
        } else if (!strcasecmp(value, "native")) {
                return AST_CC_AGENT_NATIVE;
        } else if (!strcasecmp(value, "generic")) {
                return AST_CC_AGENT_GENERIC;
        } else {
                ast_log(LOG_WARNING, "%s is an invalid value for cc_agent_policy. Switching to 'never'\n", value);
                return AST_CC_AGENT_NEVER;
        }
}

static enum ast_cc_monitor_policies str_to_monitor_policy(const char * const value)
{
        if (!strcasecmp(value, "never")) {
                return AST_CC_MONITOR_NEVER;
        } else if (!strcasecmp(value, "native")) {
                return AST_CC_MONITOR_NATIVE;
        } else if (!strcasecmp(value, "generic")) {
                return AST_CC_MONITOR_GENERIC;
        } else if (!strcasecmp(value, "always")) {
                return AST_CC_MONITOR_ALWAYS;
        } else {
                ast_log(LOG_WARNING, "%s is an invalid value for cc_monitor_policy. Switching to 'never'\n", value);
                return AST_CC_MONITOR_NEVER;
        }
}

static const char *agent_policy_to_str(enum ast_cc_agent_policies policy)
{
        switch (policy) {
        case AST_CC_AGENT_NEVER:
                return "never";
        case AST_CC_AGENT_NATIVE:
                return "native";
        case AST_CC_AGENT_GENERIC:
                return "generic";
        default:
                /* This should never happen... */
                return "";
        }
}

static const char *monitor_policy_to_str(enum ast_cc_monitor_policies policy)
{
        switch (policy) {
        case AST_CC_MONITOR_NEVER:
                return "never";
        case AST_CC_MONITOR_NATIVE:
                return "native";
        case AST_CC_MONITOR_GENERIC:
                return "generic";
        case AST_CC_MONITOR_ALWAYS:
                return "always";
        default:
                /* This should never happen... */
                return "";
        }
}
int ast_cc_get_param(struct ast_cc_config_params *params, const char * const name,
                char *buf, size_t buf_len)
{
        const char *value = NULL;

        if (!strcasecmp(name, "cc_callback_macro")) {
                value = ast_get_cc_callback_macro(params);
        } else if (!strcasecmp(name, "cc_agent_policy")) {
                value = agent_policy_to_str(ast_get_cc_agent_policy(params));
        } else if (!strcasecmp(name, "cc_monitor_policy")) {
                value = monitor_policy_to_str(ast_get_cc_monitor_policy(params));
        } else if (!strcasecmp(name, "cc_agent_dialstring")) {
                value = ast_get_cc_agent_dialstring(params);
        }
        if (value) {
                ast_copy_string(buf, value, buf_len);
                return 0;
        }

        /* The rest of these are all ints of some sort and require some
         * snprintf-itude
         */

        if (!strcasecmp(name, "cc_offer_timer")) {
                snprintf(buf, buf_len, "%u", ast_get_cc_offer_timer(params));
        } else if (!strcasecmp(name, "ccnr_available_timer")) {
                snprintf(buf, buf_len, "%u", ast_get_ccnr_available_timer(params));
        } else if (!strcasecmp(name, "ccbs_available_timer")) {
                snprintf(buf, buf_len, "%u", ast_get_ccbs_available_timer(params));
        } else if (!strcasecmp(name, "cc_max_agents")) {
                snprintf(buf, buf_len, "%u", ast_get_cc_max_agents(params));
        } else if (!strcasecmp(name, "cc_max_monitors")) {
                snprintf(buf, buf_len, "%u", ast_get_cc_max_monitors(params));
        } else if (!strcasecmp(name, "cc_recall_timer")) {
                snprintf(buf, buf_len, "%u", ast_get_cc_recall_timer(params));
        } else {
                ast_log(LOG_WARNING, "%s is not a valid CC parameter. Ignoring.\n", name);
                return -1;
        }

        return 0;
}

int ast_cc_set_param(struct ast_cc_config_params *params, const char * const name,
                const char * const value)
{
        unsigned int value_as_uint;
        if (!strcasecmp(name, "cc_agent_policy")) {
                return ast_set_cc_agent_policy(params, str_to_agent_policy(value));
        } else if (!strcasecmp(name, "cc_monitor_policy")) {
                return ast_set_cc_monitor_policy(params, str_to_monitor_policy(value));
        } else if (!strcasecmp(name, "cc_agent_dialstring")) {
                ast_set_cc_agent_dialstring(params, value);
        } else if (!strcasecmp(name, "cc_callback_macro")) {
                ast_set_cc_callback_macro(params, value);
                return 0;
        }

        if (!sscanf(value, "%30u", &value_as_uint) == 1) {
                return -1;
        }

        if (!strcasecmp(name, "cc_offer_timer")) {
                ast_set_cc_offer_timer(params, value_as_uint);
        } else if (!strcasecmp(name, "ccnr_available_timer")) {
                ast_set_ccnr_available_timer(params, value_as_uint);
        } else if (!strcasecmp(name, "ccbs_available_timer")) {
                ast_set_ccbs_available_timer(params, value_as_uint);
        } else if (!strcasecmp(name, "cc_max_agents")) {
                ast_set_cc_max_agents(params, value_as_uint);
        } else if (!strcasecmp(name, "cc_max_monitors")) {
                ast_set_cc_max_monitors(params, value_as_uint);
        } else if (!strcasecmp(name, "cc_recall_timer")) {
                ast_set_cc_recall_timer(params, value_as_uint);
        } else {
                ast_log(LOG_WARNING, "%s is not a valid CC parameter. Ignoring.\n", name);
                return -1;
        }

        return 0;
}

int ast_cc_is_config_param(const char * const name)
{
        return (!strcasecmp(name, "cc_agent_policy") ||
                                !strcasecmp(name, "cc_monitor_policy") ||
                                !strcasecmp(name, "cc_offer_timer") ||
                                !strcasecmp(name, "ccnr_available_timer") ||
                                !strcasecmp(name, "ccbs_available_timer") ||
                                !strcasecmp(name, "cc_max_agents") ||
                                !strcasecmp(name, "cc_max_monitors") ||
                                !strcasecmp(name, "cc_callback_macro") ||
                                !strcasecmp(name, "cc_agent_dialstring") ||
                                !strcasecmp(name, "cc_recall_timer"));
}

void ast_cc_copy_config_params(struct ast_cc_config_params *dest, const struct ast_cc_config_params *src)
{
        *dest = *src;
}

enum ast_cc_agent_policies ast_get_cc_agent_policy(struct ast_cc_config_params *config)
{
        return config->cc_agent_policy;
}

int ast_set_cc_agent_policy(struct ast_cc_config_params *config, enum ast_cc_agent_policies value)
{
        /* Screw C and its weak type checking for making me have to do this
         * validation at runtime.
         */
        if (value < AST_CC_AGENT_NEVER || value > AST_CC_AGENT_GENERIC) {
                return -1;
        }
        config->cc_agent_policy = value;
        return 0;
}

enum ast_cc_monitor_policies ast_get_cc_monitor_policy(struct ast_cc_config_params *config)
{
        return config->cc_monitor_policy;
}

int ast_set_cc_monitor_policy(struct ast_cc_config_params *config, enum ast_cc_monitor_policies value)
{
        /* Screw C and its weak type checking for making me have to do this
         * validation at runtime.
         */
        if (value < AST_CC_MONITOR_NEVER || value > AST_CC_MONITOR_ALWAYS) {
                return -1;
        }
        config->cc_monitor_policy = value;
        return 0;
}

unsigned int ast_get_cc_offer_timer(struct ast_cc_config_params *config)
{
        return config->cc_offer_timer;
}

void ast_set_cc_offer_timer(struct ast_cc_config_params *config, unsigned int value)
{
        /* 0 is an unreasonable value for any timer. Stick with the default */
        if (value == 0) {
                ast_log(LOG_WARNING, "0 is an invalid value for cc_offer_timer. Retaining value as %u\n", config->cc_offer_timer);
                return;
        }
        config->cc_offer_timer = value;
}

unsigned int ast_get_ccnr_available_timer(struct ast_cc_config_params *config)
{
        return config->ccnr_available_timer;
}

void ast_set_ccnr_available_timer(struct ast_cc_config_params *config, unsigned int value)
{
        /* 0 is an unreasonable value for any timer. Stick with the default */
        if (value == 0) {
                ast_log(LOG_WARNING, "0 is an invalid value for ccnr_available_timer. Retaining value as %u\n", config->ccnr_available_timer);
                return;
        }
        config->ccnr_available_timer = value;
}

unsigned int ast_get_cc_recall_timer(struct ast_cc_config_params *config)
{
        return config->cc_recall_timer;
}

void ast_set_cc_recall_timer(struct ast_cc_config_params *config, unsigned int value)
{
        /* 0 is an unreasonable value for any timer. Stick with the default */
        if (value == 0) {
                ast_log(LOG_WARNING, "0 is an invalid value for ccnr_available_timer. Retaining value as %u\n", config->cc_recall_timer);
                return;
        }
        config->cc_recall_timer = value;
}

unsigned int ast_get_ccbs_available_timer(struct ast_cc_config_params *config)
{
        return config->ccbs_available_timer;
}

void ast_set_ccbs_available_timer(struct ast_cc_config_params *config, unsigned int value)
{
        /* 0 is an unreasonable value for any timer. Stick with the default */
        if (value == 0) {
                ast_log(LOG_WARNING, "0 is an invalid value for ccbs_available_timer. Retaining value as %u\n", config->ccbs_available_timer);
                return;
        }
        config->ccbs_available_timer = value;
}

const char *ast_get_cc_agent_dialstring(struct ast_cc_config_params *config)
{
        return config->cc_agent_dialstring;
}

void ast_set_cc_agent_dialstring(struct ast_cc_config_params *config, const char *const value)
{
        if (ast_strlen_zero(value)) {
                config->cc_agent_dialstring[0] = '\0';
        } else {
                ast_copy_string(config->cc_agent_dialstring, value, sizeof(config->cc_agent_dialstring));
        }
}

unsigned int ast_get_cc_max_agents(struct ast_cc_config_params *config)
{
        return config->cc_max_agents;
}

void ast_set_cc_max_agents(struct ast_cc_config_params *config, unsigned int value)
{
        config->cc_max_agents = value;
}

unsigned int ast_get_cc_max_monitors(struct ast_cc_config_params *config)
{
        return config->cc_max_monitors;
}

void ast_set_cc_max_monitors(struct ast_cc_config_params *config, unsigned int value)
{
        config->cc_max_monitors = value;
}

const char *ast_get_cc_callback_macro(struct ast_cc_config_params *config)
{
        return config->cc_callback_macro;
}

void ast_set_cc_callback_macro(struct ast_cc_config_params *config, const char * const value)
{
        if (ast_strlen_zero(value)) {
                config->cc_callback_macro[0] = '\0';
        } else {
                ast_copy_string(config->cc_callback_macro, value, sizeof(config->cc_callback_macro));
        }
}

struct cc_monitor_backend {
        AST_LIST_ENTRY(cc_monitor_backend) next;
        const struct ast_cc_monitor_callbacks *callbacks;
};

AST_RWLIST_HEAD_STATIC(cc_monitor_backends, cc_monitor_backend);

int ast_cc_monitor_register(const struct ast_cc_monitor_callbacks *callbacks)
{
        struct cc_monitor_backend *backend = ast_calloc(1, sizeof(*backend));

        if (!backend) {
                return -1;
        }

        backend->callbacks = callbacks;

        AST_RWLIST_WRLOCK(&cc_monitor_backends);
        AST_RWLIST_INSERT_TAIL(&cc_monitor_backends, backend, next);
        AST_RWLIST_UNLOCK(&cc_monitor_backends);
        return 0;
}

static const struct ast_cc_monitor_callbacks *find_monitor_callbacks(const char * const type)
{
        struct cc_monitor_backend *backend;
        const struct ast_cc_monitor_callbacks *callbacks = NULL;

        AST_RWLIST_RDLOCK(&cc_monitor_backends);
        AST_RWLIST_TRAVERSE(&cc_monitor_backends, backend, next) {
                if (!strcmp(backend->callbacks->type, type)) {
                        ast_log_dynamic_level(cc_logger_level, "Returning monitor backend %s\n", backend->callbacks->type);
                        callbacks = backend->callbacks;
                        break;
                }
        }
        AST_RWLIST_UNLOCK(&cc_monitor_backends);
        return callbacks;
}

void ast_cc_monitor_unregister(const struct ast_cc_monitor_callbacks *callbacks)
{
        struct cc_monitor_backend *backend;
        AST_RWLIST_WRLOCK(&cc_monitor_backends);
        AST_RWLIST_TRAVERSE_SAFE_BEGIN(&cc_monitor_backends, backend, next) {
                if (backend->callbacks == callbacks) {
                        AST_RWLIST_REMOVE_CURRENT(next);
                        ast_free(backend);
                        break;
                }
        }
        AST_RWLIST_TRAVERSE_SAFE_END;
        AST_RWLIST_UNLOCK(&cc_monitor_backends);
}

struct cc_agent_backend {
        AST_LIST_ENTRY(cc_agent_backend) next;
        const struct ast_cc_agent_callbacks *callbacks;
};

AST_RWLIST_HEAD_STATIC(cc_agent_backends, cc_agent_backend);

int ast_cc_agent_register(const struct ast_cc_agent_callbacks *callbacks)
{
        struct cc_agent_backend *backend = ast_calloc(1, sizeof(*backend));

        if (!backend) {
                return -1;
        }

        backend->callbacks = callbacks;
        AST_RWLIST_WRLOCK(&cc_agent_backends);
        AST_RWLIST_INSERT_TAIL(&cc_agent_backends, backend, next);
        AST_RWLIST_UNLOCK(&cc_agent_backends);
        return 0;
}

void ast_cc_agent_unregister(const struct ast_cc_agent_callbacks *callbacks)
{
        struct cc_agent_backend *backend;
        AST_RWLIST_WRLOCK(&cc_agent_backends);
        AST_RWLIST_TRAVERSE_SAFE_BEGIN(&cc_agent_backends, backend, next) {
                if (backend->callbacks == callbacks) {
                        AST_RWLIST_REMOVE_CURRENT(next);
                        ast_free(backend);
                        break;
                }
        }
        AST_RWLIST_TRAVERSE_SAFE_END;
        AST_RWLIST_UNLOCK(&cc_agent_backends);
}

static const struct ast_cc_agent_callbacks *find_agent_callbacks(struct ast_channel *chan)
{
        struct cc_agent_backend *backend;
        const struct ast_cc_agent_callbacks *callbacks = NULL;
        struct ast_cc_config_params *cc_params;
        char type[32];

        cc_params = ast_channel_get_cc_config_params(chan);
        if (!cc_params) {
                return NULL;
        }
        switch (ast_get_cc_agent_policy(cc_params)) {
        case AST_CC_AGENT_GENERIC:
                ast_copy_string(type, "generic", sizeof(type));
                break;
        case AST_CC_AGENT_NATIVE:
                ast_channel_get_cc_agent_type(chan, type, sizeof(type));
                break;
        default:
                ast_log_dynamic_level(cc_logger_level, "Not returning agent callbacks since this channel is configured not to have a CC agent\n");
                return NULL;
        }

        AST_RWLIST_RDLOCK(&cc_agent_backends);
        AST_RWLIST_TRAVERSE(&cc_agent_backends, backend, next) {
                if (!strcmp(backend->callbacks->type, type)) {
                        ast_log_dynamic_level(cc_logger_level, "Returning agent backend %s\n", backend->callbacks->type);
                        callbacks = backend->callbacks;
                        break;
                }
        }
        AST_RWLIST_UNLOCK(&cc_agent_backends);
        return callbacks;
}

/*!
 * \internal
 * \brief Determine if the given device state is considered available by generic CCSS.
 * \since 1.8
 *
 * \param state Device state to test.
 *
 * \return TRUE if the given device state is considered available by generic CCSS.
 */
static int cc_generic_is_device_available(enum ast_device_state state)
{
        return state == AST_DEVICE_NOT_INUSE || state == AST_DEVICE_UNKNOWN;
}

static int cc_generic_monitor_request_cc(struct ast_cc_monitor *monitor, int *available_timer_id);
static int cc_generic_monitor_suspend(struct ast_cc_monitor *monitor);
static int cc_generic_monitor_unsuspend(struct ast_cc_monitor *monitor);
static int cc_generic_monitor_cancel_available_timer(struct ast_cc_monitor *monitor, int *sched_id);
static void cc_generic_monitor_destructor(void *private_data);

static struct ast_cc_monitor_callbacks generic_monitor_cbs = {
        .type = "generic",
        .request_cc = cc_generic_monitor_request_cc,
        .suspend = cc_generic_monitor_suspend,
        .unsuspend = cc_generic_monitor_unsuspend,
        .cancel_available_timer = cc_generic_monitor_cancel_available_timer,
        .destructor = cc_generic_monitor_destructor,
};

struct ao2_container *generic_monitors;

struct generic_monitor_instance {
        int core_id;
        int is_suspended;
        int monitoring;
        AST_LIST_ENTRY(generic_monitor_instance) next;
};

struct generic_monitor_instance_list {
        const char *device_name;
        enum ast_device_state current_state;
        /* If there are multiple instances monitoring the
         * same device and one should fail, we need to know
         * whether to signal that the device can be recalled.
         * The problem is that the device state is not enough
         * to check. If a caller has requested CCNR, then the
         * fact that the device is available does not indicate
         * that the device is ready to be recalled. Instead, as
         * soon as one instance of the monitor becomes available
         * for a recall, we mark the entire list as being fit
         * for recall. If a CCNR request comes in, then we will
         * have to mark the list as unfit for recall since this
         * is a clear indicator that the person at the monitored
         * device has gone away and is actuall not fit to be
         * recalled
         */
        int fit_for_recall;
        struct ast_event_sub *sub;
        AST_LIST_HEAD_NOLOCK(, generic_monitor_instance) list;
};

/*!
 * \brief private data for generic device monitor
 */
struct generic_monitor_pvt {
        /*!
         * We need the device name during destruction so we
         * can find the appropriate item to destroy.
         */
        const char *device_name;
        /*!
         * We need the core ID for similar reasons. Once we
         * find the appropriate item in our ao2_container, we
         * need to remove the appropriate cc_monitor from the
         * list of monitors.
         */
        int core_id;
};

static int generic_monitor_hash_fn(const void *obj, const int flags)
{
        const struct generic_monitor_instance_list *generic_list = obj;
        return ast_str_hash(generic_list->device_name);
}

static int generic_monitor_cmp_fn(void *obj, void *arg, int flags)
{
        const struct generic_monitor_instance_list *generic_list1 = obj;
        const struct generic_monitor_instance_list *generic_list2 = arg;

        return !strcmp(generic_list1->device_name, generic_list2->device_name) ? CMP_MATCH | CMP_STOP : 0;
}

static struct generic_monitor_instance_list *find_generic_monitor_instance_list(const char * const device_name)
{
        struct generic_monitor_instance_list finder = {.device_name = device_name};

        return ao2_t_find(generic_monitors, &finder, OBJ_POINTER, "Finding generic monitor instance list");
}

static void generic_monitor_instance_list_destructor(void *obj)
{
        struct generic_monitor_instance_list *generic_list = obj;
        struct generic_monitor_instance *generic_instance;

        generic_list->sub = ast_event_unsubscribe(generic_list->sub);
        while ((generic_instance = AST_LIST_REMOVE_HEAD(&generic_list->list, next))) {
                ast_free(generic_instance);
        }
        ast_free((char *)generic_list->device_name);
}

static void generic_monitor_devstate_cb(const struct ast_event *event, void *userdata);
static struct generic_monitor_instance_list *create_new_generic_list(struct ast_cc_monitor *monitor)
{
        struct generic_monitor_instance_list *generic_list = ao2_t_alloc(sizeof(*generic_list),
                        generic_monitor_instance_list_destructor, "allocate generic monitor instance list");

        if (!generic_list) {
                return NULL;
        }

        if (!(generic_list->device_name = ast_strdup(monitor->interface->device_name))) {
                cc_unref(generic_list, "Failed to strdup the monitor's device name");
                return NULL;
        }

        if (!(generic_list->sub = ast_event_subscribe(AST_EVENT_DEVICE_STATE,
                generic_monitor_devstate_cb, "Requesting CC", NULL,
                AST_EVENT_IE_DEVICE, AST_EVENT_IE_PLTYPE_STR, monitor->interface->device_name,
                AST_EVENT_IE_STATE, AST_EVENT_IE_PLTYPE_EXISTS,
                AST_EVENT_IE_END))) {
                cc_unref(generic_list, "Failed to subscribe to device state");
                return NULL;
        }
        generic_list->current_state = ast_device_state(monitor->interface->device_name);
        ao2_t_link(generic_monitors, generic_list, "linking new generic monitor instance list");
        return generic_list;
}

struct generic_tp_cb_data {
        const char *device_name;
        enum ast_device_state new_state;
};

static int generic_monitor_devstate_tp_cb(void *data)
{
        struct generic_tp_cb_data *gtcd = data;
        enum ast_device_state new_state = gtcd->new_state;
        enum ast_device_state previous_state = gtcd->new_state;
        const char *monitor_name = gtcd->device_name;
        struct generic_monitor_instance_list *generic_list;
        struct generic_monitor_instance *generic_instance;

        if (!(generic_list = find_generic_monitor_instance_list(monitor_name))) {
                /* The most likely cause for this is that we destroyed the monitor in the
                 * time between subscribing to its device state and the time this executes.
                 * Not really a big deal.
                 */
                ast_free((char *) gtcd->device_name);
                ast_free(gtcd);
                return 0;
        }

        if (generic_list->current_state == new_state) {
                /* The device state hasn't actually changed, so we don't really care */
                cc_unref(generic_list, "Kill reference of generic list in devstate taskprocessor callback");
                ast_free((char *) gtcd->device_name);
                ast_free(gtcd);
                return 0;
        }

        previous_state = generic_list->current_state;
        generic_list->current_state = new_state;

        if (cc_generic_is_device_available(new_state) &&
                        (previous_state == AST_DEVICE_INUSE || previous_state == AST_DEVICE_UNAVAILABLE ||
                         previous_state == AST_DEVICE_BUSY)) {
                AST_LIST_TRAVERSE(&generic_list->list, generic_instance, next) {
                        if (!generic_instance->is_suspended && generic_instance->monitoring) {
                                generic_instance->monitoring = 0;
                                generic_list->fit_for_recall = 1;
                                ast_cc_monitor_callee_available(generic_instance->core_id, "Generic monitored party has become available");
                                break;
                        }
                }
        }
        cc_unref(generic_list, "Kill reference of generic list in devstate taskprocessor callback");
        ast_free((char *) gtcd->device_name);
        ast_free(gtcd);
        return 0;
}

static void generic_monitor_devstate_cb(const struct ast_event *event, void *userdata)
{
        /* Wow, it's cool that we've picked up on a state change, but we really want
         * the actual work to be done in the core's taskprocessor execution thread
         * so that all monitor operations can be serialized. Locks?! We don't need
         * no steenkin' locks!
         */
        struct generic_tp_cb_data *gtcd = ast_calloc(1, sizeof(*gtcd));

        if (!gtcd) {
                return;
        }

        if (!(gtcd->device_name = ast_strdup(ast_event_get_ie_str(event, AST_EVENT_IE_DEVICE)))) {
                ast_free(gtcd);
                return;
        }
        gtcd->new_state = ast_event_get_ie_uint(event, AST_EVENT_IE_STATE);

        if (ast_taskprocessor_push(cc_core_taskprocessor, generic_monitor_devstate_tp_cb, gtcd)) {
                ast_free((char *)gtcd->device_name);
                ast_free(gtcd);
        }
}

int ast_cc_available_timer_expire(const void *data)
{
        struct ast_cc_monitor *monitor = (struct ast_cc_monitor *) data;
        int res;
        monitor->available_timer_id = -1;
        res = ast_cc_monitor_failed(monitor->core_id, monitor->interface->device_name, "Available timer expired for monitor");
        cc_unref(monitor, "Unref reference from scheduler\n");
        return res;
}

static int cc_generic_monitor_request_cc(struct ast_cc_monitor *monitor, int *available_timer_id)
{
        struct generic_monitor_instance_list *generic_list;
        struct generic_monitor_instance *generic_instance;
        struct generic_monitor_pvt *gen_mon_pvt;
        enum ast_cc_service_type service = monitor->service_offered;
        int when;

        /* First things first. Native channel drivers will have their private data allocated
         * at the time that they tell the core that they can offer CC. Generic is quite a bit
         * different, and we wait until this point to allocate our private data.
         */
        if (!(gen_mon_pvt = ast_calloc(1, sizeof(*gen_mon_pvt)))) {
                return -1;
        }

        if (!(gen_mon_pvt->device_name = ast_strdup(monitor->interface->device_name))) {
                ast_free(gen_mon_pvt);
                return -1;
        }

        gen_mon_pvt->core_id = monitor->core_id;

        monitor->private_data = gen_mon_pvt;

        if (!(generic_list = find_generic_monitor_instance_list(monitor->interface->device_name))) {
                if (!(generic_list = create_new_generic_list(monitor))) {
                        return -1;
                }
        }

        if (!(generic_instance = ast_calloc(1, sizeof(*generic_instance)))) {
                /* The generic monitor destructor will take care of the appropriate
                 * deallocations
                 */
                cc_unref(generic_list, "Generic monitor instance failed to allocate");
                return -1;
        }
        generic_instance->core_id = monitor->core_id;
        generic_instance->monitoring = 1;
        AST_LIST_INSERT_TAIL(&generic_list->list, generic_instance, next);
        when = service == AST_CC_CCBS ? ast_get_ccbs_available_timer(monitor->interface->config_params) :
                ast_get_ccnr_available_timer(monitor->interface->config_params);

        *available_timer_id = ast_sched_add(cc_sched_context, when * 1000,
                        ast_cc_available_timer_expire, cc_ref(monitor, "Give the scheduler a monitor reference"));
        if (*available_timer_id == -1) {
                cc_unref(monitor, "Failed to schedule available timer. (monitor)");
                cc_unref(generic_list, "Failed to schedule available timer. (generic_list)");
                return -1;
        }
        /* If the new instance was created as CCNR, then that means this device is not currently
         * fit for recall even if it previously was.
         */
        if (service == AST_CC_CCNR || service == AST_CC_CCNL) {
                generic_list->fit_for_recall = 0;
        }
        ast_cc_monitor_request_acked(monitor->core_id, "Generic monitor for %s subscribed to device state.",
                        monitor->interface->device_name);
        cc_unref(generic_list, "Finished with monitor instance reference in request cc callback");
        return 0;
}

static int cc_generic_monitor_suspend(struct ast_cc_monitor *monitor)
{
        struct generic_monitor_instance_list *generic_list;
        struct generic_monitor_instance *generic_instance;
        enum ast_device_state state = ast_device_state(monitor->interface->device_name);

        if (!(generic_list = find_generic_monitor_instance_list(monitor->interface->device_name))) {
                return -1;
        }

        /* First we need to mark this particular monitor as being suspended. */
        AST_LIST_TRAVERSE(&generic_list->list, generic_instance, next) {
                if (generic_instance->core_id == monitor->core_id) {
                        generic_instance->is_suspended = 1;
                        break;
                }
        }

        /* If the device being suspended is currently in use, then we don't need to
         * take any further actions
         */
        if (!cc_generic_is_device_available(state)) {
                cc_unref(generic_list, "Device is in use. Nothing to do. Unref generic list.");
                return 0;
        }

        /* If the device is not in use, though, then it may be possible to report the
         * device's availability using a different monitor which is monitoring the
         * same device
         */

        AST_LIST_TRAVERSE(&generic_list->list, generic_instance, next) {
                if (!generic_instance->is_suspended) {
                        ast_cc_monitor_callee_available(generic_instance->core_id, "Generic monitored party has become available");
                        break;
                }
        }
        cc_unref(generic_list, "Done with generic list in suspend callback");
        return 0;
}

static int cc_generic_monitor_unsuspend(struct ast_cc_monitor *monitor)
{
        struct generic_monitor_instance *generic_instance;
        struct generic_monitor_instance_list *generic_list = find_generic_monitor_instance_list(monitor->interface->device_name);
        enum ast_device_state state = ast_device_state(monitor->interface->device_name);

        if (!generic_list) {
                return -1;
        }
        /* If the device is currently available, we can immediately announce
         * its availability
         */
        if (cc_generic_is_device_available(state)) {
                ast_cc_monitor_callee_available(monitor->core_id, "Generic monitored party has become available");
        }

        /* In addition, we need to mark this generic_monitor_instance as not being suspended anymore */
        AST_LIST_TRAVERSE(&generic_list->list, generic_instance, next) {
                if (generic_instance->core_id == monitor->core_id) {
                        generic_instance->is_suspended = 0;
                        generic_instance->monitoring = 1;
                        break;
                }
        }
        cc_unref(generic_list, "Done with generic list in cc_generic_monitor_unsuspend");
        return 0;
}

static int cc_generic_monitor_cancel_available_timer(struct ast_cc_monitor *monitor, int *sched_id)
{
        ast_assert(sched_id != NULL);

        if (*sched_id == -1) {
                return 0;
        }

        ast_log_dynamic_level(cc_logger_level, "Core %d: Canceling generic monitor available timer for monitor %s\n",
                        monitor->core_id, monitor->interface->device_name);
        if (!ast_sched_del(cc_sched_context, *sched_id)) {
                cc_unref(monitor, "Remove scheduler's reference to the monitor");
        }
        *sched_id = -1;
        return 0;
}

static void cc_generic_monitor_destructor(void *private_data)
{
        struct generic_monitor_pvt *gen_mon_pvt = private_data;
        struct generic_monitor_instance_list *generic_list;
        struct generic_monitor_instance *generic_instance;

        if (!private_data) {
                /* If the private data is NULL, that means that the monitor hasn't even
                 * been created yet, but that the destructor was called. While this sort
                 * of behavior is useful for native monitors, with a generic one, there is
                 * nothing in particular to do.
                 */
                return;
        }

        ast_log_dynamic_level(cc_logger_level, "Core %d: Destroying generic monitor %s\n",
                        gen_mon_pvt->core_id, gen_mon_pvt->device_name);

        if (!(generic_list = find_generic_monitor_instance_list(gen_mon_pvt->device_name))) {
                /* If there's no generic list, that means that the monitor is being destroyed
                 * before we actually got to request CC. Not a biggie. Same in the situation
                 * below if the list traversal should complete without finding an entry.
                 */
                ast_free((char *)gen_mon_pvt->device_name);
                ast_free(gen_mon_pvt);
                return;
        }

        AST_LIST_TRAVERSE_SAFE_BEGIN(&generic_list->list, generic_instance, next) {
                if (generic_instance->core_id == gen_mon_pvt->core_id) {
                        AST_LIST_REMOVE_CURRENT(next);
                        ast_free(generic_instance);
                        break;
                }
        }
        AST_LIST_TRAVERSE_SAFE_END;

        if (AST_LIST_EMPTY(&generic_list->list)) {
                /* No more monitors with this device name exist. Time to unlink this
                 * list from the container
                 */
                ao2_t_unlink(generic_monitors, generic_list, "Generic list is empty. Unlink it from the container");
        } else {
                /* There are still instances for this particular device. The situation
                 * may be that we were attempting a CC recall and a failure occurred, perhaps
                 * on the agent side. If a failure happens here and the device being monitored
                 * is available, then we need to signal on the first unsuspended instance that
                 * the device is available for recall.
                 */

                /* First things first. We don't even want to consider this action if
                 * the device in question isn't available right now.
                 */
                if (generic_list->fit_for_recall
                        && cc_generic_is_device_available(generic_list->current_state)) {
                        AST_LIST_TRAVERSE(&generic_list->list, generic_instance, next) {
                                if (!generic_instance->is_suspended && generic_instance->monitoring) {
                                        ast_cc_monitor_callee_available(generic_instance->core_id, "Signaling generic monitor "
                                                        "availability due to other instance's failure.");
                                        break;
                                }
                        }
                }
        }
        cc_unref(generic_list, "Done with generic list in generic monitor destructor");
        ast_free((char *)gen_mon_pvt->device_name);
        ast_free(gen_mon_pvt);
}

static void cc_interface_destroy(void *data)
{
        struct ast_cc_interface *interface = data;
        ast_log_dynamic_level(cc_logger_level, "Destroying cc interface %s\n", interface->device_name);
        ast_cc_config_params_destroy(interface->config_params);
}

/*!
 * \brief Data regarding an extension monitor's child's dialstrings
 *
 * \details
 * In developing CCSS, we had most aspects of its operation finished,
 * but there was one looming problem that we had failed to get right.
 * In our design document, we stated that when a CC recall occurs, all
 * endpoints that had been dialed originally would be called back.
 * Unfortunately, our implementation only allowed for devices which had
 * active monitors to inhabit the CC_INTERFACES channel variable, thus
 * making the automated recall only call monitored devices.
 *
 * Devices that were not CC-capable, or devices which failed CC at some
 * point during the process would not make it into the CC_INTERFACES
 * channel variable. This struct is meant as a remedy for the problem.
 */
struct extension_child_dialstring {
        /*!
         * \brief the original dialstring used to call a particular device
         *
         * \details
         * When someone dials a particular endpoint, the dialstring used in
         * the dialplan is copied into this buffer. What's important here is
         * that this is the ORIGINAL dialstring, not the dialstring saved on
         * a device monitor. The dialstring on a device monitor is what should
         * be used when recalling that device. The two dialstrings may not be
         * the same.
         *
         * By keeping a copy of the original dialstring used, we can fall back
         * to using it if the device either does not ever offer CC or if the
         * device at some point fails for some reason, such as a timer expiration.
         */
        char original_dialstring[AST_CHANNEL_NAME];
        /*!
         * \brief The name of the device being dialed
         *
         * \details
         * This serves mainly as a key when searching for a particular dialstring.
         * For instance, let's say that we have called device SIP/400@somepeer. This
         * device offers call completion, but then due to some unforeseen circumstance,
         * this device backs out and makes CC unavailable. When that happens, we need
         * to find the dialstring that corresponds to that device, and we use the
         * stored device name as a way to find it.
         *
         * \note There is one particular case where the device name stored here
         * will be empty. This is the case where we fail to request a channel, but we
         * still can make use of generic call completion. In such a case, since we never
         * were able to request the channel, we can't find what its device name is. In
         * this case, however, it is not important because the dialstring is guaranteed
         * to be the same both here and in the device monitor.
         */
        char device_name[AST_CHANNEL_NAME];
        /*!
         * \brief Is this structure valid for use in CC_INTERFACES?
         *
         * \details
         * When this structure is first created, all information stored here is planned
         * to be used, so we set the is_valid flag. However, if a device offers call
         * completion, it will potentially have its own dialstring to use for the recall,
         * so we find this structure and clear the is_valid flag. By clearing the is_valid
         * flag, we won't try to populate the CC_INTERFACES variable with the dialstring
         * stored in this struct. Now, if later, the device which had offered CC should fail,
         * perhaps due to a timer expiration, then we need to re-set the is_valid flag. This
         * way, we still will end up placing a call to the device again, and the dialstring
         * used will be the same as was originally used.
         */
        int is_valid;
        AST_LIST_ENTRY(extension_child_dialstring) next;
};

/*!
 * \brief Private data for an extension monitor
 */
struct extension_monitor_pvt {
        AST_LIST_HEAD_NOLOCK(, extension_child_dialstring) child_dialstrings;
};

static void cc_extension_monitor_destructor(void *private_data)
{
        struct extension_monitor_pvt *extension_pvt = private_data;
        struct extension_child_dialstring *child_dialstring;

        /* This shouldn't be possible, but I'm paranoid */
        if (!extension_pvt) {
                return;
        }

        while ((child_dialstring = AST_LIST_REMOVE_HEAD(&extension_pvt->child_dialstrings, next))) {
                ast_free(child_dialstring);
        }
        ast_free(extension_pvt);
}

static void cc_monitor_destroy(void *data)
{
        struct ast_cc_monitor *monitor = data;
        /* During the monitor creation process, it is possible for this
         * function to be called prior to when callbacks are assigned
         * to the monitor. Also, extension monitors do not have callbacks
         * assigned to them, so we wouldn't want to segfault when we try
         * to destroy one of them.
         */
        ast_log_dynamic_level(cc_logger_level, "Core %d: Calling destructor for monitor %s\n",
                        monitor->core_id, monitor->interface->device_name);
        if (monitor->interface->monitor_class == AST_CC_EXTENSION_MONITOR) {
                cc_extension_monitor_destructor(monitor->private_data);
        }
        if (monitor->callbacks) {
                monitor->callbacks->destructor(monitor->private_data);
        }
        cc_unref(monitor->interface, "Unreffing tree's reference to interface");
        ast_free(monitor->dialstring);
}

static void cc_interface_tree_destroy(void *data)
{
        struct cc_monitor_tree *cc_interface_tree = data;
        struct ast_cc_monitor *monitor;
        while ((monitor = AST_LIST_REMOVE_HEAD(cc_interface_tree, next))) {
                if (monitor->callbacks) {
                        monitor->callbacks->cancel_available_timer(monitor, &monitor->available_timer_id);
                }
                cc_unref(monitor, "Destroying all monitors");
        }
        AST_LIST_HEAD_DESTROY(cc_interface_tree);
}

/*!
 * This counter is used for assigning unique ids
 * to CC-enabled dialed interfaces.
 */
static int dialed_cc_interface_counter;

/*!
 * \internal
 * \brief data stored in CC datastore
 *
 * The datastore creates a list of interfaces that were
 * dialed, including both extensions and devices. In addition
 * to the intrinsic data of the tree, some extra information
 * is needed for use by app_dial.
 */
struct dialed_cc_interfaces {
        /*!
         * This value serves a dual-purpose. When dial starts, if the
         * dialed_cc_interfaces datastore currently exists on the calling
         * channel, then the dial_parent_id will serve as a means of
         * letting the new extension cc_monitor we create know
         * who his parent is. This value will be the extension
         * cc_monitor that dialed the local channel that resulted
         * in the new Dial app being called.
         *
         * In addition, once an extension cc_monitor is created,
         * the dial_parent_id will be changed to the id of that newly
         * created interface. This way, device interfaces created from
         * receiving AST_CONTROL_CC frames can use this field to determine
         * who their parent extension interface should be.
         */
        unsigned int dial_parent_id;
        /*!
         * Identifier for the potential CC request that may be made
         * based on this call. Even though an instance of the core may
         * not be made (since the caller may not request CC), we allocate
         * a new core_id at the beginning of the call so that recipient
         * channel drivers can have the information handy just in case
         * the caller does end up requesting CC.
         */
        int core_id;
        /*!
         * When a new Dial application is started, and the datastore
         * already exists on the channel, we can determine if we
         * should be adding any new interface information to tree.
         */
        char ignore;
        /*!
         * When it comes time to offer CC to the caller, we only want to offer
         * it to the original incoming channel. For nested Dials and outbound
         * channels, it is incorrect to attempt such a thing. This flag indicates
         * if the channel to which this datastore is attached may be legally
         * offered CC when the call is finished.
         */
        char is_original_caller;
        /*!
         * Reference-counted "tree" of interfaces.
         */
        struct cc_monitor_tree *interface_tree;
};

/*!
 * \internal
 * \brief Destructor function for cc_interfaces datastore
 *
 * This function will free the actual datastore and drop
 * the refcount for the monitor tree by one. In cases
 * where CC can actually be used, this unref will not
 * result in the destruction of the monitor tree, because
 * the CC core will still have a reference.
 *
 * \param data The dialed_cc_interfaces struct to destroy
 */
static void dialed_cc_interfaces_destroy(void *data)
{
        struct dialed_cc_interfaces *cc_interfaces = data;
        cc_unref(cc_interfaces->interface_tree, "Unref dial's ref to monitor tree");
        ast_free(cc_interfaces);
}

/*!
 * \internal
 * \brief Duplicate callback for cc_interfaces datastore
 *
 * Integers are copied by value, but the monitor tree
 * is done via a shallow copy and a bump of the refcount.
 * This way, sub-Dials will be appending interfaces onto
 * the same list as this call to Dial.
 *
 * \param data The old dialed_cc_interfaces we want to copy
 * \retval NULL Could not allocate memory for new dialed_cc_interfaces
 * \retval non-NULL The new copy of the dialed_cc_interfaces
 */
static void *dialed_cc_interfaces_duplicate(void *data)
{
        struct dialed_cc_interfaces *old_cc_interfaces = data;
        struct dialed_cc_interfaces *new_cc_interfaces = ast_calloc(1, sizeof(*new_cc_interfaces));
        if (!new_cc_interfaces) {
                return NULL;
        }
        new_cc_interfaces->ignore = old_cc_interfaces->ignore;
        new_cc_interfaces->dial_parent_id = old_cc_interfaces->dial_parent_id;
        new_cc_interfaces->is_original_caller = 0;
        cc_ref(old_cc_interfaces->interface_tree, "New ref due to duplication of monitor tree");
        new_cc_interfaces->core_id = old_cc_interfaces->core_id;
        new_cc_interfaces->interface_tree = old_cc_interfaces->interface_tree;
        return new_cc_interfaces;
}

/*!
 * \internal
 * \brief information regarding the dialed_cc_interfaces datastore
 *
 * The dialed_cc_interfaces datastore is responsible for keeping track
 * of what CC-enabled interfaces have been dialed by the caller. For
 * more information regarding the actual structure of the tree, see
 * the documentation provided in include/asterisk/ccss.h
 */
static const struct ast_datastore_info dialed_cc_interfaces_info = {
        .type = "Dial CC Interfaces",
        .duplicate = dialed_cc_interfaces_duplicate,
        .destroy = dialed_cc_interfaces_destroy,
};

static struct extension_monitor_pvt *extension_monitor_pvt_init(void)
{
        struct extension_monitor_pvt *ext_pvt = ast_calloc(1, sizeof(*ext_pvt));
        if (!ext_pvt) {
                return NULL;
        }
        AST_LIST_HEAD_INIT_NOLOCK(&ext_pvt->child_dialstrings);
        return ext_pvt;
}

void ast_cc_extension_monitor_add_dialstring(struct ast_channel *incoming, const char * const dialstring, const char * const device_name)
{
        struct ast_datastore *cc_datastore;
        struct dialed_cc_interfaces *cc_interfaces;
        struct ast_cc_monitor *monitor;
        struct extension_monitor_pvt *extension_pvt;
        struct extension_child_dialstring *child_dialstring;
        struct cc_monitor_tree *interface_tree;
        int id;

        ast_channel_lock(incoming);
        if (!(cc_datastore = ast_channel_datastore_find(incoming, &dialed_cc_interfaces_info, NULL))) {
                ast_channel_unlock(incoming);
                return;
        }

        cc_interfaces = cc_datastore->data;
        interface_tree = cc_interfaces->interface_tree;
        id = cc_interfaces->dial_parent_id;
        ast_channel_unlock(incoming);

        AST_LIST_LOCK(interface_tree);
        AST_LIST_TRAVERSE(interface_tree, monitor, next) {
                if (monitor->id == id) {
                        break;
                }
        }

        if (!monitor) {
                AST_LIST_UNLOCK(interface_tree);
                return;
        }

        extension_pvt = monitor->private_data;
        if (!(child_dialstring = ast_calloc(1, sizeof(*child_dialstring)))) {
                AST_LIST_UNLOCK(interface_tree);
                return;
        }
        ast_copy_string(child_dialstring->original_dialstring, dialstring, sizeof(child_dialstring->original_dialstring));
        ast_copy_string(child_dialstring->device_name, device_name, sizeof(child_dialstring->device_name));
        child_dialstring->is_valid = 1;
        AST_LIST_INSERT_TAIL(&extension_pvt->child_dialstrings, child_dialstring, next);
        AST_LIST_UNLOCK(interface_tree);
}

static void cc_extension_monitor_change_is_valid(struct cc_core_instance *core_instance, unsigned int parent_id, const char * const device_name, int is_valid)
{
        struct ast_cc_monitor *monitor_iter;
        struct extension_monitor_pvt *extension_pvt;
        struct extension_child_dialstring *child_dialstring;

        AST_LIST_TRAVERSE(core_instance->monitors, monitor_iter, next) {
                if (monitor_iter->id == parent_id) {
                        break;
                }
        }

        if (!monitor_iter) {
                return;
        }
        extension_pvt = monitor_iter->private_data;

        AST_LIST_TRAVERSE(&extension_pvt->child_dialstrings, child_dialstring, next) {
                if (!strcmp(child_dialstring->device_name, device_name)) {
                        child_dialstring->is_valid = is_valid;
                        break;
                }
        }
}

/*!
 * \internal
 * \brief Allocate and initialize an "extension" interface for CC purposes
 *
 * When app_dial starts, this function is called in order to set up the
 * information about the extension in which this Dial is occurring. Any
 * devices dialed will have this particular cc_monitor as a parent.
 *
 * \param exten Extension from which Dial is occurring
 * \param context Context to which exten belongs
 * \param parent_id What should we set the parent_id of this interface to?
 * \retval NULL Memory allocation failure
 * \retval non-NULL The newly-created cc_monitor for the extension
 */
static struct ast_cc_monitor *cc_extension_monitor_init(const char * const exten, const char * const context, const unsigned int parent_id)
{
        struct ast_str *str = ast_str_alloca(2 * AST_MAX_EXTENSION);
        struct ast_cc_interface *cc_interface;
        struct ast_cc_monitor *monitor;

        ast_str_set(&str, 0, "%s@%s", exten, context);

        if (!(cc_interface = ao2_t_alloc(sizeof(*cc_interface) + ast_str_strlen(str), cc_interface_destroy,
                                        "Allocating new ast_cc_interface"))) {
                return NULL;
        }

        if (!(monitor = ao2_t_alloc(sizeof(*monitor), cc_monitor_destroy, "Allocating new ast_cc_monitor"))) {
                cc_unref(cc_interface, "failed to allocate the monitor, so unref the interface");
                return NULL;
        }

        if (!(monitor->private_data = extension_monitor_pvt_init())) {
                cc_unref(monitor, "Failed to initialize extension monitor private data. uref monitor");
                cc_unref(cc_interface, "Failed to initialize extension monitor private data. unref cc_interface");
        }

        monitor->id = ast_atomic_fetchadd_int(&dialed_cc_interface_counter, +1);
        monitor->parent_id = parent_id;
        cc_interface->monitor_type = "extension";
        cc_interface->monitor_class = AST_CC_EXTENSION_MONITOR;
        strcpy(cc_interface->device_name, ast_str_buffer(str));
        monitor->interface = cc_interface;
        ast_log_dynamic_level(cc_logger_level, "Created an extension cc interface for '%s' with id %d and parent %d\n", cc_interface->device_name, monitor->id, monitor->parent_id);
        return monitor;
}

/*!
 * \internal
 * \brief allocate dialed_cc_interfaces datastore and initialize fields
 *
 * This function is called when Situation 1 occurs in ast_cc_call_init.
 * See that function for more information on what Situation 1 is.
 *
 * In this particular case, we have to do a lot of memory allocation in order
 * to create the datastore, the data for the datastore, the tree of interfaces
 * that we'll be adding to, and the initial extension interface for this Dial
 * attempt.
 *
 * \param chan The channel onto which the datastore should be added.
 * \retval -1 An error occurred
 * \retval 0 Success
 */
static int cc_interfaces_datastore_init(struct ast_channel *chan) {
        struct dialed_cc_interfaces *interfaces;
        struct ast_cc_monitor *monitor;
        struct ast_datastore *dial_cc_datastore;

        /*XXX This may be a bit controversial. In an attempt to not allocate
         * extra resources, I make sure that a future request will be within
         * limits. The problem here is that it is reasonable to think that
         * even if we're not within the limits at this point, we may be by
         * the time the requestor will have made his request. This may be
         * deleted at some point.
         */
        if (!ast_cc_request_is_within_limits()) {
                return 0;
        }

        if (!(interfaces = ast_calloc(1, sizeof(*interfaces)))) {
                return -1;
        }

        if (!(monitor = cc_extension_monitor_init(S_OR(ast_channel_macroexten(chan), ast_channel_exten(chan)), S_OR(ast_channel_macrocontext(chan), ast_channel_context(chan)), 0))) {
                ast_free(interfaces);
                return -1;
        }

        if (!(dial_cc_datastore = ast_datastore_alloc(&dialed_cc_interfaces_info, NULL))) {
                cc_unref(monitor, "Could not allocate the dialed interfaces datastore. Unreffing monitor");
                ast_free(interfaces);
                return -1;
        }

        if (!(interfaces->interface_tree = ao2_t_alloc(sizeof(*interfaces->interface_tree), cc_interface_tree_destroy,
                                        "Allocate monitor tree"))) {
                ast_datastore_free(dial_cc_datastore);
                cc_unref(monitor, "Could not allocate monitor tree on dialed interfaces datastore. Unreffing monitor");
                ast_free(interfaces);
                return -1;
        }

        /* Finally, all that allocation is done... */
        AST_LIST_HEAD_INIT(interfaces->interface_tree);
        AST_LIST_INSERT_TAIL(interfaces->interface_tree, monitor, next);
        cc_ref(monitor, "List's reference to extension monitor");
        dial_cc_datastore->data = interfaces;
        dial_cc_datastore->inheritance = DATASTORE_INHERIT_FOREVER;
        interfaces->dial_parent_id = monitor->id;
        interfaces->core_id = monitor->core_id = ast_atomic_fetchadd_int(&core_id_counter, +1);
        interfaces->is_original_caller = 1;
        ast_channel_lock(chan);
        ast_channel_datastore_add(chan, dial_cc_datastore);
        ast_channel_unlock(chan);
        cc_unref(monitor, "Unreffing allocation's reference");
        return 0;
}

/*!
 * \internal
 * \brief  Call a monitor's destructor before the monitor has been allocated
 * \since 1.8
 *
 * \param monitor_type The type of monitor callbacks to use when calling the destructor
 * \param private_data Data allocated by a channel driver that must be freed
 *
 * \details
 * I'll admit, this is a bit evil.
 *
 * When a channel driver determines that it can offer a call completion service to
 * a caller, it is very likely that the channel driver will need to allocate some
 * data so that when the time comes to request CC, the channel driver will have the
 * necessary data at hand.
 *
 * The problem is that there are many places where failures may occur before the monitor
 * has been properly allocated and had its callbacks assigned to it. If one of these
 * failures should occur, then we still need to let the channel driver know that it
 * must destroy the data that it allocated.
 *
 * \return Nothing
 */
static void call_destructor_with_no_monitor(const char * const monitor_type, void *private_data)
{
        const struct ast_cc_monitor_callbacks *monitor_callbacks = find_monitor_callbacks(monitor_type);

        if (!monitor_callbacks) {
                return;
        }

        monitor_callbacks->destructor(private_data);
}

/*!
 * \internal
 * \brief Allocate and intitialize a device cc_monitor
 *
 * For all intents and purposes, this is the same as
 * cc_extension_monitor_init, except that there is only
 * a single parameter used for naming the interface.
 *
 * This function is called when handling AST_CONTROL_CC frames.
 * The device has reported that CC is possible, so we add it
 * to the interface_tree.
 *
 * Note that it is not necessarily erroneous to add the same
 * device to the tree twice. If the same device is called by
 * two different extension during the same call, then
 * that is a legitimate situation. Of course, I'm pretty sure
 * the dialed_interfaces global datastore will not allow that
 * to happen anyway.
 *
 * \param device_name The name of the device being added to the tree
 * \param dialstring The dialstring used to dial the device being added
 * \param parent_id The parent of this new tree node.
 * \retval NULL Memory allocation failure
 * \retval non-NULL The new ast_cc_interface created.
 */
static struct ast_cc_monitor *cc_device_monitor_init(const char * const device_name, const char * const dialstring, const struct cc_control_payload *cc_data, int core_id)
{
        struct ast_cc_interface *cc_interface;
        struct ast_cc_monitor *monitor;
        size_t device_name_len = strlen(device_name);
        int parent_id = cc_data->parent_interface_id;

        if (!(cc_interface = ao2_t_alloc(sizeof(*cc_interface) + device_name_len, cc_interface_destroy,
                                        "Allocating new ast_cc_interface"))) {
                return NULL;
        }

        if (!(cc_interface->config_params = ast_cc_config_params_init())) {
                cc_unref(cc_interface, "Failed to allocate config params, unref interface");
                return NULL;
        }

        if (!(monitor = ao2_t_alloc(sizeof(*monitor), cc_monitor_destroy, "Allocating new ast_cc_monitor"))) {
                cc_unref(cc_interface, "Failed to allocate monitor, unref interface");
                return NULL;
        }

        if (!(monitor->dialstring = ast_strdup(dialstring))) {
                cc_unref(monitor, "Failed to copy dialable name. Unref monitor");
                cc_unref(cc_interface, "Failed to copy dialable name");
                return NULL;
        }

        if (!(monitor->callbacks = find_monitor_callbacks(cc_data->monitor_type))) {
                cc_unref(monitor, "Failed to find monitor callbacks. Unref monitor");
                cc_unref(cc_interface, "Failed to find monitor callbacks");
                return NULL;
        }

        strcpy(cc_interface->device_name, device_name);
        monitor->id = ast_atomic_fetchadd_int(&dialed_cc_interface_counter, +1);
        monitor->parent_id = parent_id;
        monitor->core_id = core_id;
        monitor->service_offered = cc_data->service;
        monitor->private_data = cc_data->private_data;
        cc_interface->monitor_type = cc_data->monitor_type;
        cc_interface->monitor_class = AST_CC_DEVICE_MONITOR;
        monitor->interface = cc_interface;
        monitor->available_timer_id = -1;
        ast_cc_copy_config_params(cc_interface->config_params, &cc_data->config_params);
        ast_log_dynamic_level(cc_logger_level, "Core %d: Created a device cc interface for '%s' with id %d and parent %d\n",
                        monitor->core_id, cc_interface->device_name, monitor->id, monitor->parent_id);
        return monitor;
}

/*!
 * \details
 * Unless we are ignoring CC for some reason, we will always
 * call this function when we read an AST_CONTROL_CC frame
 * from an outbound channel.
 *
 * This function will call cc_device_monitor_init to
 * create the new cc_monitor for the device from which
 * we read the frame. In addition, the new device will be added
 * to the monitor tree on the dialed_cc_interfaces datastore
 * on the inbound channel.
 *
 * If this is the first AST_CONTROL_CC frame that we have handled
 * for this call, then we will also initialize the CC core for
 * this call.
 */
void ast_handle_cc_control_frame(struct ast_channel *inbound, struct ast_channel *outbound, void *frame_data)
{
        char *device_name;
        char *dialstring;
        struct ast_cc_monitor *monitor;
        struct ast_datastore *cc_datastore;
        struct dialed_cc_interfaces *cc_interfaces;
        struct cc_control_payload *cc_data = frame_data;
        struct cc_core_instance *core_instance;

        device_name = cc_data->device_name;
        dialstring = cc_data->dialstring;

        ast_channel_lock(inbound);
        if (!(cc_datastore = ast_channel_datastore_find(inbound, &dialed_cc_interfaces_info, NULL))) {
                ast_log(LOG_WARNING, "Unable to retrieve CC datastore while processing CC frame from '%s'. CC services will be unavailable.\n", device_name);
                ast_channel_unlock(inbound);
                call_destructor_with_no_monitor(cc_data->monitor_type, cc_data->private_data);
                return;
        }

        cc_interfaces = cc_datastore->data;

        if (cc_interfaces->ignore) {
                ast_channel_unlock(inbound);
                call_destructor_with_no_monitor(cc_data->monitor_type, cc_data->private_data);
                return;
        }

        if (!cc_interfaces->is_original_caller) {
                /* If the is_original_caller is not set on the *inbound* channel, then
                 * it must be a local channel. As such, we do not want to create a core instance
                 * or an agent for the local channel. Instead, we want to pass this along to the
                 * other side of the local channel so that the original caller can benefit.
                 */
                ast_channel_unlock(inbound);
                ast_indicate_data(inbound, AST_CONTROL_CC, cc_data, sizeof(*cc_data));
                return;
        }

        core_instance = find_cc_core_instance(cc_interfaces->core_id);
        if (!core_instance) {
                core_instance = cc_core_init_instance(inbound, cc_interfaces->interface_tree,
                        cc_interfaces->core_id, cc_data);
                if (!core_instance) {
                        cc_interfaces->ignore = 1;
                        ast_channel_unlock(inbound);
                        call_destructor_with_no_monitor(cc_data->monitor_type, cc_data->private_data);
                        return;
                }
        }

        ast_channel_unlock(inbound);

        /* Yeah this kind of sucks, but luckily most people
         * aren't dialing thousands of interfaces on every call
         *
         * This traversal helps us to not create duplicate monitors in
         * case a device queues multiple CC control frames.
         */
        AST_LIST_LOCK(cc_interfaces->interface_tree);
        AST_LIST_TRAVERSE(cc_interfaces->interface_tree, monitor, next) {
                if (!strcmp(monitor->interface->device_name, device_name)) {
                        ast_log_dynamic_level(cc_logger_level, "Core %d: Device %s sent us multiple CC control frames. Ignoring those beyond the first.\n",
                                        core_instance->core_id, device_name);
                        AST_LIST_UNLOCK(cc_interfaces->interface_tree);
                        cc_unref(core_instance, "Returning early from ast_handle_cc_control_frame. Unref core_instance");
                        call_destructor_with_no_monitor(cc_data->monitor_type, cc_data->private_data);
                        return;
                }
        }
        AST_LIST_UNLOCK(cc_interfaces->interface_tree);

        if (!(monitor = cc_device_monitor_init(device_name, dialstring, cc_data, core_instance->core_id))) {
                ast_log(LOG_WARNING, "Unable to create CC device interface for '%s'. CC services will be unavailable on this interface.\n", device_name);
                cc_unref(core_instance, "Returning early from ast_handle_cc_control_frame. Unref core_instance");
                call_destructor_with_no_monitor(cc_data->monitor_type, cc_data->private_data);
                return;
        }

        AST_LIST_LOCK(cc_interfaces->interface_tree);
        cc_ref(monitor, "monitor tree's reference to the monitor");
        AST_LIST_INSERT_TAIL(cc_interfaces->interface_tree, monitor, next);
        AST_LIST_UNLOCK(cc_interfaces->interface_tree);

        cc_extension_monitor_change_is_valid(core_instance, monitor->parent_id, monitor->interface->device_name, 0);

        manager_event(EVENT_FLAG_CC, "CCAvailable",
                "CoreID: %d\r\n"
                "Callee: %s\r\n"
                "Service: %s\r\n",
                cc_interfaces->core_id, device_name, cc_service_to_string(cc_data->service)
        );

        cc_unref(core_instance, "Done with core_instance after handling CC control frame");
        cc_unref(monitor, "Unref reference from allocating monitor");
}

int ast_cc_call_init(struct ast_channel *chan, int *ignore_cc)
{
        /* There are three situations to deal with here:
         *
         * 1. The channel does not have a dialed_cc_interfaces datastore on
         * it. This means that this is the first time that Dial has
         * been called. We need to create/initialize the datastore.
         *
         * 2. The channel does have a cc_interface datastore on it and
         * the "ignore" indicator is 0. This means that a Local channel
         * was called by a "parent" dial. We can check the datastore's
         * parent field to see who the root of this particular dial tree
         * is.
         *
         * 3. The channel does have a cc_interface datastore on it and
         * the "ignore" indicator is 1. This means that a second Dial call
         * is being made from an extension. In this case, we do not
         * want to make any additions/modifications to the datastore. We
         * will instead set a flag to indicate that CCSS is completely
         * disabled for this Dial attempt.
         */

        struct ast_datastore *cc_interfaces_datastore;
        struct dialed_cc_interfaces *interfaces;
        struct ast_cc_monitor *monitor;
        struct ast_cc_config_params *cc_params;

        ast_channel_lock(chan);

        cc_params = ast_channel_get_cc_config_params(chan);
        if (!cc_params) {
                ast_channel_unlock(chan);
                return -1;
        }
        if (ast_get_cc_agent_policy(cc_params) == AST_CC_AGENT_NEVER) {
                /* We can't offer CC to this caller anyway, so don't bother with CC on this call
                 */
                *ignore_cc = 1;
                ast_channel_unlock(chan);
                ast_log_dynamic_level(cc_logger_level, "Agent policy for %s is 'never'. CC not possible\n", ast_channel_name(chan));
                return 0;
        }

        if (!(cc_interfaces_datastore = ast_channel_datastore_find(chan, &dialed_cc_interfaces_info, NULL))) {
                /* Situation 1 has occurred */
                ast_channel_unlock(chan);
                return cc_interfaces_datastore_init(chan);
        }
        interfaces = cc_interfaces_datastore->data;
        ast_channel_unlock(chan);

        if (interfaces->ignore) {
                /* Situation 3 has occurred */
                *ignore_cc = 1;
                ast_log_dynamic_level(cc_logger_level, "Datastore is present with ignore flag set. Ignoring CC offers on this call\n");
                return 0;
        }

        /* Situation 2 has occurred */
        if (!(monitor = cc_extension_monitor_init(S_OR(ast_channel_macroexten(chan), ast_channel_exten(chan)),
                        S_OR(ast_channel_macrocontext(chan), ast_channel_context(chan)), interfaces->dial_parent_id))) {
                return -1;
        }
        monitor->core_id = interfaces->core_id;
        AST_LIST_LOCK(interfaces->interface_tree);
        cc_ref(monitor, "monitor tree's reference to the monitor");
        AST_LIST_INSERT_TAIL(interfaces->interface_tree, monitor, next);
        AST_LIST_UNLOCK(interfaces->interface_tree);
        interfaces->dial_parent_id = monitor->id;
        cc_unref(monitor, "Unref monitor's allocation reference");
        return 0;
}

int ast_cc_request_is_within_limits(void)
{
        return cc_request_count < global_cc_max_requests;
}

int ast_cc_get_current_core_id(struct ast_channel *chan)
{
        struct ast_datastore *datastore;
        struct dialed_cc_interfaces *cc_interfaces;
        int core_id_return;

        ast_channel_lock(chan);
        if (!(datastore = ast_channel_datastore_find(chan, &dialed_cc_interfaces_info, NULL))) {
                ast_channel_unlock(chan);
                return -1;
        }

        cc_interfaces = datastore->data;
        core_id_return = cc_interfaces->ignore ? -1 : cc_interfaces->core_id;
        ast_channel_unlock(chan);
        return core_id_return;

}

static long count_agents(const char * const caller, const int core_id_exception)
{
        struct count_agents_cb_data data = {.core_id_exception = core_id_exception,};

        ao2_t_callback_data(cc_core_instances, OBJ_NODATA, count_agents_cb, (char *)caller, &data, "Counting agents");
        ast_log_dynamic_level(cc_logger_level, "Counted %d agents\n", data.count);
        return data.count;
}

static void kill_duplicate_offers(char *caller)
{
        unsigned long match_flags = MATCH_NO_REQUEST;
        struct ao2_iterator *dups_iter;

        /*
         * Must remove the ref that was in cc_core_instances outside of
         * the container lock to prevent deadlock.
         */
        dups_iter = ao2_t_callback_data(cc_core_instances, OBJ_MULTIPLE | OBJ_UNLINK,
                match_agent, caller, &match_flags, "Killing duplicate offers");
        if (dups_iter) {
                /* Now actually unref any duplicate offers by simply destroying the iterator. */
                ao2_iterator_destroy(dups_iter);
        }
}

static void check_callback_sanity(const struct ast_cc_agent_callbacks *callbacks)
{
        ast_assert(callbacks->init != NULL);
        ast_assert(callbacks->start_offer_timer != NULL);
        ast_assert(callbacks->stop_offer_timer != NULL);
        ast_assert(callbacks->respond != NULL);
        ast_assert(callbacks->status_request != NULL);
        ast_assert(callbacks->start_monitoring != NULL);
        ast_assert(callbacks->callee_available != NULL);
        ast_assert(callbacks->destructor != NULL);
}

static void agent_destroy(void *data)
{
        struct ast_cc_agent *agent = data;

        if (agent->callbacks) {
                agent->callbacks->destructor(agent);
        }
        ast_cc_config_params_destroy(agent->cc_params);
}

static struct ast_cc_agent *cc_agent_init(struct ast_channel *caller_chan,
                const char * const caller_name, const int core_id,
                struct cc_monitor_tree *interface_tree)
{
        struct ast_cc_agent *agent;
        struct ast_cc_config_params *cc_params;

        if (!(agent = ao2_t_alloc(sizeof(*agent) + strlen(caller_name), agent_destroy,
                                        "Allocating new ast_cc_agent"))) {
                return NULL;
        }

        agent->core_id = core_id;
        strcpy(agent->device_name, caller_name);

        cc_params = ast_channel_get_cc_config_params(caller_chan);
        if (!cc_params) {
                cc_unref(agent, "Could not get channel config params.");
                return NULL;
        }
        if (!(agent->cc_params = ast_cc_config_params_init())) {
                cc_unref(agent, "Could not init agent config params.");
                return NULL;
        }
        ast_cc_copy_config_params(agent->cc_params, cc_params);

        if (!(agent->callbacks = find_agent_callbacks(caller_chan))) {
                cc_unref(agent, "Could not find agent callbacks.");
                return NULL;
        }
        check_callback_sanity(agent->callbacks);

        if (agent->callbacks->init(agent, caller_chan)) {
                cc_unref(agent, "Agent init callback failed.");
                return NULL;
        }
        ast_log_dynamic_level(cc_logger_level, "Core %d: Created an agent for caller %s\n",
                        agent->core_id, agent->device_name);
        return agent;
}

/* Generic agent callbacks */
static int cc_generic_agent_init(struct ast_cc_agent *agent, struct ast_channel *chan);
static int cc_generic_agent_start_offer_timer(struct ast_cc_agent *agent);
static int cc_generic_agent_stop_offer_timer(struct ast_cc_agent *agent);
static void cc_generic_agent_respond(struct ast_cc_agent *agent, enum ast_cc_agent_response_reason reason);
static int cc_generic_agent_status_request(struct ast_cc_agent *agent);
static int cc_generic_agent_stop_ringing(struct ast_cc_agent *agent);
static int cc_generic_agent_start_monitoring(struct ast_cc_agent *agent);
static int cc_generic_agent_recall(struct ast_cc_agent *agent);
static void cc_generic_agent_destructor(struct ast_cc_agent *agent);

static struct ast_cc_agent_callbacks generic_agent_callbacks = {
        .type = "generic",
        .init = cc_generic_agent_init,
        .start_offer_timer = cc_generic_agent_start_offer_timer,
        .stop_offer_timer = cc_generic_agent_stop_offer_timer,
        .respond = cc_generic_agent_respond,
        .status_request = cc_generic_agent_status_request,
        .stop_ringing = cc_generic_agent_stop_ringing,
        .start_monitoring = cc_generic_agent_start_monitoring,
        .callee_available = cc_generic_agent_recall,
        .destructor = cc_generic_agent_destructor,
};

struct cc_generic_agent_pvt {
        /*!
         * Subscription to device state
         *
         * Used in the CC_CALLER_BUSY state. The
         * generic agent will subscribe to the
         * device state of the caller in order to
         * determine when we may move on
         */
        struct ast_event_sub *sub;
        /*!
         * Scheduler id of offer timer.
         */
        int offer_timer_id;
        /*!
         * Caller ID number
         *
         * When we re-call the caller, we need
         * to provide this information to
         * ast_request_and_dial so that the
         * information will be present in the
         * call to the callee
         */
        char cid_num[AST_CHANNEL_NAME];
        /*!
         * Caller ID name
         *
         * See the description of cid_num.
         * The same applies here, except this
         * is the caller's name.
         */
        char cid_name[AST_CHANNEL_NAME];
        /*!
         * Extension dialed
         *
         * The original extension dialed. This is used
         * so that when performing a recall, we can
         * call the proper extension.
         */
        char exten[AST_CHANNEL_NAME];
        /*!
         * Context dialed
         *
         * The original context dialed. This is used
         * so that when performaing a recall, we can
         * call into the proper context
         */
        char context[AST_CHANNEL_NAME];
};

static int cc_generic_agent_init(struct ast_cc_agent *agent, struct ast_channel *chan)
{
        struct cc_generic_agent_pvt *generic_pvt = ast_calloc(1, sizeof(*generic_pvt));

        if (!generic_pvt) {
                return -1;
        }

        generic_pvt->offer_timer_id = -1;
        if (chan->caller.id.number.valid && chan->caller.id.number.str) {
                ast_copy_string(generic_pvt->cid_num, chan->caller.id.number.str, sizeof(generic_pvt->cid_num));
        }
        if (chan->caller.id.name.valid && chan->caller.id.name.str) {
                ast_copy_string(generic_pvt->cid_name, chan->caller.id.name.str, sizeof(generic_pvt->cid_name));
        }
        ast_copy_string(generic_pvt->exten, S_OR(ast_channel_macroexten(chan), ast_channel_exten(chan)), sizeof(generic_pvt->exten));
        ast_copy_string(generic_pvt->context, S_OR(ast_channel_macrocontext(chan), ast_channel_context(chan)), sizeof(generic_pvt->context));
        agent->private_data = generic_pvt;
        ast_set_flag(agent, AST_CC_AGENT_SKIP_OFFER);
        return 0;
}

static int offer_timer_expire(const void *data)
{
        struct ast_cc_agent *agent = (struct ast_cc_agent *) data;
        struct cc_generic_agent_pvt *agent_pvt = agent->private_data;
        ast_log_dynamic_level(cc_logger_level, "Core %d: Queuing change request because offer timer has expired.\n",
                        agent->core_id);
        agent_pvt->offer_timer_id = -1;
        ast_cc_failed(agent->core_id, "Generic agent %s offer timer expired", agent->device_name);
        cc_unref(agent, "Remove scheduler's reference to the agent");
        return 0;
}

static int cc_generic_agent_start_offer_timer(struct ast_cc_agent *agent)
{
        int when;
        int sched_id;
        struct cc_generic_agent_pvt *generic_pvt = agent->private_data;

        ast_assert(cc_sched_context != NULL);
        ast_assert(agent->cc_params != NULL);

        when = ast_get_cc_offer_timer(agent->cc_params) * 1000;
        ast_log_dynamic_level(cc_logger_level, "Core %d: About to schedule offer timer expiration for %d ms\n",
                        agent->core_id, when);
        if ((sched_id = ast_sched_add(cc_sched_context, when, offer_timer_expire, cc_ref(agent, "Give scheduler an agent ref"))) == -1) {
                return -1;
        }
        generic_pvt->offer_timer_id = sched_id;
        return 0;
}

static int cc_generic_agent_stop_offer_timer(struct ast_cc_agent *agent)
{
        struct cc_generic_agent_pvt *generic_pvt = agent->private_data;

        if (generic_pvt->offer_timer_id != -1) {
                if (!ast_sched_del(cc_sched_context, generic_pvt->offer_timer_id)) {
                        cc_unref(agent, "Remove scheduler's reference to the agent");
                }
                generic_pvt->offer_timer_id = -1;
        }
        return 0;
}

static void cc_generic_agent_respond(struct ast_cc_agent *agent, enum ast_cc_agent_response_reason reason)
{
        /* The generic agent doesn't have to do anything special to
         * acknowledge a CC request. Just return.
         */
        return;
}

static int cc_generic_agent_status_request(struct ast_cc_agent *agent)
{
        ast_cc_agent_status_response(agent->core_id, ast_device_state(agent->device_name));
        return 0;
}

static int cc_generic_agent_stop_ringing(struct ast_cc_agent *agent)
{
        struct ast_channel *recall_chan = ast_channel_get_by_name_prefix(agent->device_name, strlen(agent->device_name));

        if (!recall_chan) {
                return 0;
        }

        ast_softhangup(recall_chan, AST_SOFTHANGUP_EXPLICIT);
        return 0;
}

static int generic_agent_devstate_unsubscribe(void *data)
{
        struct ast_cc_agent *agent = data;
        struct cc_generic_agent_pvt *generic_pvt = agent->private_data;

        if (generic_pvt->sub != NULL) {
                generic_pvt->sub = ast_event_unsubscribe(generic_pvt->sub);
        }
        cc_unref(agent, "Done unsubscribing from devstate");
        return 0;
}

static void generic_agent_devstate_cb(const struct ast_event *event, void *userdata)
{
        struct ast_cc_agent *agent = userdata;
        enum ast_device_state new_state;

        new_state = ast_event_get_ie_uint(event, AST_EVENT_IE_STATE);
        if (!cc_generic_is_device_available(new_state)) {
                /* Not interested in this new state of the device.  It is still busy. */
                return;
        }

        /* We can't unsubscribe from device state events here because it causes a deadlock */
        if (ast_taskprocessor_push(cc_core_taskprocessor, generic_agent_devstate_unsubscribe,
                        cc_ref(agent, "ref agent for device state unsubscription"))) {
                cc_unref(agent, "Unref agent unsubscribing from devstate failed");
        }
        ast_cc_agent_caller_available(agent->core_id, "%s is no longer busy", agent->device_name);
}

static int cc_generic_agent_start_monitoring(struct ast_cc_agent *agent)
{
        struct cc_generic_agent_pvt *generic_pvt = agent->private_data;
        struct ast_str *str = ast_str_alloca(128);

        ast_assert(generic_pvt->sub == NULL);
        ast_str_set(&str, 0, "Agent monitoring %s device state since it is busy\n",
                agent->device_name);

        if (!(generic_pvt->sub = ast_event_subscribe(AST_EVENT_DEVICE_STATE,
                generic_agent_devstate_cb, ast_str_buffer(str), agent,
                AST_EVENT_IE_DEVICE, AST_EVENT_IE_PLTYPE_STR, agent->device_name,
                AST_EVENT_IE_STATE, AST_EVENT_IE_PLTYPE_EXISTS,
                AST_EVENT_IE_END))) {
                return -1;
        }
        return 0;
}

static void *generic_recall(void *data)
{
        struct ast_cc_agent *agent = data;
        struct cc_generic_agent_pvt *generic_pvt = agent->private_data;
        const char *interface = S_OR(ast_get_cc_agent_dialstring(agent->cc_params), ast_strdupa(agent->device_name));
        const char *tech;
        char *target;
        int reason;
        struct ast_channel *chan;
        const char *callback_macro = ast_get_cc_callback_macro(agent->cc_params);
        unsigned int recall_timer = ast_get_cc_recall_timer(agent->cc_params) * 1000;
        struct ast_format tmp_fmt;
        struct ast_format_cap *tmp_cap = ast_format_cap_alloc_nolock();

        if (!tmp_cap) {
                return NULL;
        }

        tech = interface;
        if ((target = strchr(interface, '/'))) {
                *target++ = '\0';
        }

        ast_format_cap_add(tmp_cap, ast_format_set(&tmp_fmt, AST_FORMAT_SLINEAR, 0));
        if (!(chan = ast_request_and_dial(tech, tmp_cap, NULL, target, recall_timer, &reason, generic_pvt->cid_num, generic_pvt->cid_name))) {
                /* Hmm, no channel. Sucks for you, bud.
                 */
                ast_log_dynamic_level(cc_logger_level, "Core %d: Failed to call back %s for reason %d\n",
                                agent->core_id, agent->device_name, reason);
                ast_cc_failed(agent->core_id, "Failed to call back device %s/%s", tech, target);
                ast_format_cap_destroy(tmp_cap);
                return NULL;
        }
        ast_format_cap_destroy(tmp_cap);
        
        /* We have a channel. It's time now to set up the datastore of recalled CC interfaces.
         * This will be a common task for all recall functions. If it were possible, I'd have
         * the core do it automatically, but alas I cannot. Instead, I will provide a public
         * function to do so.
         */
        ast_setup_cc_recall_datastore(chan, agent->core_id);
        ast_cc_agent_set_interfaces_chanvar(chan);

        ast_channel_exten_set(chan, generic_pvt->exten);
        ast_channel_context_set(chan, generic_pvt->context);
        ast_channel_priority_set(chan, 1);

        pbx_builtin_setvar_helper(chan, "CC_EXTEN", generic_pvt->exten);
        pbx_builtin_setvar_helper(chan, "CC_CONTEXT", generic_pvt->context);

        if (!ast_strlen_zero(callback_macro)) {
                ast_log_dynamic_level(cc_logger_level, "Core %d: There's a callback macro configured for agent %s\n",
                                agent->core_id, agent->device_name);
                if (ast_app_run_macro(NULL, chan, callback_macro, NULL)) {
                        ast_cc_failed(agent->core_id, "Callback macro to %s failed. Maybe a hangup?", agent->device_name);
                        ast_hangup(chan);
                        return NULL;
                }
        }
        ast_cc_agent_recalling(agent->core_id, "Generic agent %s is recalling", agent->device_name);
        ast_pbx_start(chan);
        return NULL;
}

static int cc_generic_agent_recall(struct ast_cc_agent *agent)
{
        pthread_t clotho;
        enum ast_device_state current_state = ast_device_state(agent->device_name);

        if (!cc_generic_is_device_available(current_state)) {
                /* We can't try to contact the device right now because he's not available
                 * Let the core know he's busy.
                 */
                ast_cc_agent_caller_busy(agent->core_id, "Generic agent caller %s is busy", agent->device_name);
                return 0;
        }
        ast_pthread_create_detached_background(&clotho, NULL, generic_recall, agent);
        return 0;
}

static void cc_generic_agent_destructor(struct ast_cc_agent *agent)
{
        struct cc_generic_agent_pvt *agent_pvt = agent->private_data;

        if (!agent_pvt) {
                /* The agent constructor probably failed. */
                return;
        }

        cc_generic_agent_stop_offer_timer(agent);
        if (agent_pvt->sub) {
                agent_pvt->sub = ast_event_unsubscribe(agent_pvt->sub);
        }

        ast_free(agent_pvt);
}

static void cc_core_instance_destructor(void *data)
{
        struct cc_core_instance *core_instance = data;
        ast_log_dynamic_level(cc_logger_level, "Core %d: Destroying core instance\n", core_instance->core_id);
        if (core_instance->agent) {
                cc_unref(core_instance->agent, "Core instance is done with the agent now");
        }
        if (core_instance->monitors) {
                core_instance->monitors = cc_unref(core_instance->monitors, "Core instance is done with interface list");
        }
}

static struct cc_core_instance *cc_core_init_instance(struct ast_channel *caller_chan,
                struct cc_monitor_tree *called_tree, const int core_id, struct cc_control_payload *cc_data)
{
        char caller[AST_CHANNEL_NAME];
        struct cc_core_instance *core_instance;
        struct ast_cc_config_params *cc_params;
        long agent_count;
        int recall_core_id;

        ast_channel_get_device_name(caller_chan, caller, sizeof(caller));
        cc_params = ast_channel_get_cc_config_params(caller_chan);
        if (!cc_params) {
                ast_log_dynamic_level(cc_logger_level, "Could not get CC parameters for %s\n",
                        caller);
                return NULL;
        }
        /* First, we need to kill off other pending CC offers from caller. If the caller is going
         * to request a CC service, it may only be for the latest call he made.
         */
        if (ast_get_cc_agent_policy(cc_params) == AST_CC_AGENT_GENERIC) {
                kill_duplicate_offers(caller);
        }

        ast_cc_is_recall(caller_chan, &recall_core_id, NULL);
        agent_count = count_agents(caller, recall_core_id);
        if (agent_count >= ast_get_cc_max_agents(cc_params)) {
                ast_log_dynamic_level(cc_logger_level, "Caller %s already has the maximum number of agents configured\n", caller);
                return NULL;
        }

        /* Generic agents can only have a single outstanding CC request per caller. */
        if (agent_count > 0 && ast_get_cc_agent_policy(cc_params) == AST_CC_AGENT_GENERIC) {
                ast_log_dynamic_level(cc_logger_level, "Generic agents can only have a single outstanding request\n");
                return NULL;
        }

        /* Next, we need to create the core instance for this call */
        if (!(core_instance = ao2_t_alloc(sizeof(*core_instance), cc_core_instance_destructor, "Creating core instance for CC"))) {
                return NULL;
        }

        core_instance->core_id = core_id;
        if (!(core_instance->agent = cc_agent_init(caller_chan, caller, core_instance->core_id, called_tree))) {
                cc_unref(core_instance, "Couldn't allocate agent, unref core_instance");
                return NULL;
        }

        core_instance->monitors = cc_ref(called_tree, "Core instance getting ref to monitor tree");

        ao2_t_link(cc_core_instances, core_instance, "Link core instance into container");

        return core_instance;
}

struct cc_state_change_args {
        struct cc_core_instance *core_instance;/*!< Holds reference to core instance. */
        enum cc_state state;
        int core_id;
        char debug[1];
};

static int is_state_change_valid(enum cc_state current_state, const enum cc_state new_state, struct ast_cc_agent *agent)
{
        int is_valid = 0;
        switch (new_state) {
        case CC_AVAILABLE:
                ast_log_dynamic_level(cc_logger_level, "Core %d: Asked to change to state %d? That should never happen.\n",
                                agent->core_id, new_state);
                break;
        case CC_CALLER_OFFERED:
                if (current_state == CC_AVAILABLE) {
                        is_valid = 1;
                }
                break;
        case CC_CALLER_REQUESTED:
                if (current_state == CC_CALLER_OFFERED ||
                                (current_state == CC_AVAILABLE && ast_test_flag(agent, AST_CC_AGENT_SKIP_OFFER))) {
                        is_valid = 1;
                }
                break;
        case CC_ACTIVE:
                if (current_state == CC_CALLER_REQUESTED || current_state == CC_CALLER_BUSY) {
                        is_valid = 1;
                }
                break;
        case CC_CALLEE_READY:
                if (current_state == CC_ACTIVE) {
                        is_valid = 1;
                }
                break;
        case CC_CALLER_BUSY:
                if (current_state == CC_CALLEE_READY) {
                        is_valid = 1;
                }
                break;
        case CC_RECALLING:
                if (current_state == CC_CALLEE_READY) {
                        is_valid = 1;
                }
                break;
        case CC_COMPLETE:
                if (current_state == CC_RECALLING) {
                        is_valid = 1;
                }
                break;
        case CC_FAILED:
                is_valid = 1;
                break;
        default:
                ast_log_dynamic_level(cc_logger_level, "Core %d: Asked to change to unknown state %d\n",
                                agent->core_id, new_state);
                break;
        }

        return is_valid;
}

static int cc_available(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        /* This should never happen... */
        ast_log(LOG_WARNING, "Someone requested to change to CC_AVAILABLE? Ignoring.\n");
        return -1;
}

static int cc_caller_offered(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        if (core_instance->agent->callbacks->start_offer_timer(core_instance->agent)) {
                ast_cc_failed(core_instance->core_id, "Failed to start the offer timer for %s\n",
                                core_instance->agent->device_name);
                return -1;
        }
        manager_event(EVENT_FLAG_CC, "CCOfferTimerStart",
                "CoreID: %d\r\n"
                "Caller: %s\r\n"
                "Expires: %u\r\n",
                core_instance->core_id, core_instance->agent->device_name, core_instance->agent->cc_params->cc_offer_timer);
        ast_log_dynamic_level(cc_logger_level, "Core %d: Started the offer timer for the agent %s!\n",
                        core_instance->core_id, core_instance->agent->device_name);
        return 0;
}

/*!
 * \brief check if the core instance has any device monitors
 *
 * In any case where we end up removing a device monitor from the
 * list of device monitors, it is important to see what the state
 * of the list is afterwards. If we find that we only have extension
 * monitors left, then no devices are actually being monitored.
 * In such a case, we need to declare that CC has failed for this
 * call. This function helps those cases to determine if they should
 * declare failure.
 *
 * \param core_instance The core instance we are checking for the existence
 * of device monitors
 * \retval 0 No device monitors exist on this core_instance
 * \retval 1 There is still at least 1 device monitor remaining
 */
static int has_device_monitors(struct cc_core_instance *core_instance)
{
        struct ast_cc_monitor *iter;
        int res = 0;

        AST_LIST_TRAVERSE(core_instance->monitors, iter, next) {
                if (iter->interface->monitor_class == AST_CC_DEVICE_MONITOR) {
                        res = 1;
                        break;
                }
        }

        return res;
}

static void request_cc(struct cc_core_instance *core_instance)
{
        struct ast_cc_monitor *monitor_iter;
        AST_LIST_LOCK(core_instance->monitors);
        AST_LIST_TRAVERSE_SAFE_BEGIN(core_instance->monitors, monitor_iter, next) {
                if (monitor_iter->interface->monitor_class == AST_CC_DEVICE_MONITOR) {
                        if (monitor_iter->callbacks->request_cc(monitor_iter, &monitor_iter->available_timer_id)) {
                                AST_LIST_REMOVE_CURRENT(next);
                                cc_extension_monitor_change_is_valid(core_instance, monitor_iter->parent_id,
                                                monitor_iter->interface->device_name, 1);
                                cc_unref(monitor_iter, "request_cc failed. Unref list's reference to monitor");
                        } else {
                                manager_event(EVENT_FLAG_CC, "CCRequested",
                                        "CoreID: %d\r\n"
                                        "Caller: %s\r\n"
                                        "Callee: %s\r\n",
                                        core_instance->core_id, core_instance->agent->device_name, monitor_iter->interface->device_name);
                        }
                }
        }
        AST_LIST_TRAVERSE_SAFE_END;

        if (!has_device_monitors(core_instance)) {
                ast_cc_failed(core_instance->core_id, "All device monitors failed to request CC");
        }
        AST_LIST_UNLOCK(core_instance->monitors);
}

static int cc_caller_requested(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        if (!ast_cc_request_is_within_limits()) {
                ast_log(LOG_WARNING, "Cannot request CC since there is no more room for requests\n");
                core_instance->agent->callbacks->respond(core_instance->agent,
                        AST_CC_AGENT_RESPONSE_FAILURE_TOO_MANY);
                ast_cc_failed(core_instance->core_id, "Too many requests in the system");
                return -1;
        }
        core_instance->agent->callbacks->stop_offer_timer(core_instance->agent);
        request_cc(core_instance);
        return 0;
}

static void unsuspend(struct cc_core_instance *core_instance)
{
        struct ast_cc_monitor *monitor_iter;
        AST_LIST_LOCK(core_instance->monitors);
        AST_LIST_TRAVERSE_SAFE_BEGIN(core_instance->monitors, monitor_iter, next) {
                if (monitor_iter->interface->monitor_class == AST_CC_DEVICE_MONITOR) {
                        if (monitor_iter->callbacks->unsuspend(monitor_iter)) {
                                AST_LIST_REMOVE_CURRENT(next);
                                cc_extension_monitor_change_is_valid(core_instance, monitor_iter->parent_id,
                                                monitor_iter->interface->device_name, 1);
                                cc_unref(monitor_iter, "unsuspend failed. Unref list's reference to monitor");
                        }
                }
        }
        AST_LIST_TRAVERSE_SAFE_END;

        if (!has_device_monitors(core_instance)) {
                ast_cc_failed(core_instance->core_id, "All device monitors failed to unsuspend CC");
        }
        AST_LIST_UNLOCK(core_instance->monitors);
}

static int cc_active(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        /* Either
         * 1. Callee accepted CC request, call agent's ack callback.
         * 2. Caller became available, call agent's stop_monitoring callback and
         *    call monitor's unsuspend callback.
         */
        if (previous_state == CC_CALLER_REQUESTED) {
                core_instance->agent->callbacks->respond(core_instance->agent,
                        AST_CC_AGENT_RESPONSE_SUCCESS);
                manager_event(EVENT_FLAG_CC, "CCRequestAcknowledged",
                        "CoreID: %d\r\n"
                        "Caller: %s\r\n",
                        core_instance->core_id, core_instance->agent->device_name);
        } else if (previous_state == CC_CALLER_BUSY) {
                manager_event(EVENT_FLAG_CC, "CCCallerStopMonitoring",
                        "CoreID: %d\r\n"
                        "Caller: %s\r\n",
                        core_instance->core_id, core_instance->agent->device_name);
                unsuspend(core_instance);
        }
        /* Not possible for previous_state to be anything else due to the is_state_change_valid check at the beginning */
        return 0;
}

static int cc_callee_ready(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        core_instance->agent->callbacks->callee_available(core_instance->agent);
        return 0;
}

static void suspend(struct cc_core_instance *core_instance)
{
        struct ast_cc_monitor *monitor_iter;
        AST_LIST_LOCK(core_instance->monitors);
        AST_LIST_TRAVERSE_SAFE_BEGIN(core_instance->monitors, monitor_iter, next) {
                if (monitor_iter->interface->monitor_class == AST_CC_DEVICE_MONITOR) {
                        if (monitor_iter->callbacks->suspend(monitor_iter)) {
                                AST_LIST_REMOVE_CURRENT(next);
                                cc_extension_monitor_change_is_valid(core_instance, monitor_iter->parent_id,
                                                monitor_iter->interface->device_name, 1);
                                cc_unref(monitor_iter, "suspend failed. Unref list's reference to monitor");
                        }
                }
        }
        AST_LIST_TRAVERSE_SAFE_END;

        if (!has_device_monitors(core_instance)) {
                ast_cc_failed(core_instance->core_id, "All device monitors failed to suspend CC");
        }
        AST_LIST_UNLOCK(core_instance->monitors);
}

static int cc_caller_busy(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        /* Callee was available, but caller was busy, call agent's begin_monitoring callback
         * and call monitor's suspend callback.
         */
        suspend(core_instance);
        core_instance->agent->callbacks->start_monitoring(core_instance->agent);
        manager_event(EVENT_FLAG_CC, "CCCallerStartMonitoring",
                "CoreID: %d\r\n"
                "Caller: %s\r\n",
                core_instance->core_id, core_instance->agent->device_name);
        return 0;
}

static void cancel_available_timer(struct cc_core_instance *core_instance)
{
        struct ast_cc_monitor *monitor_iter;
        AST_LIST_LOCK(core_instance->monitors);
        AST_LIST_TRAVERSE_SAFE_BEGIN(core_instance->monitors, monitor_iter, next) {
                if (monitor_iter->interface->monitor_class == AST_CC_DEVICE_MONITOR) {
                        if (monitor_iter->callbacks->cancel_available_timer(monitor_iter, &monitor_iter->available_timer_id)) {
                                AST_LIST_REMOVE_CURRENT(next);
                                cc_extension_monitor_change_is_valid(core_instance, monitor_iter->parent_id,
                                                monitor_iter->interface->device_name, 1);
                                cc_unref(monitor_iter, "cancel_available_timer failed. Unref list's reference to monitor");
                        }
                }
        }
        AST_LIST_TRAVERSE_SAFE_END;

        if (!has_device_monitors(core_instance)) {
                ast_cc_failed(core_instance->core_id, "All device monitors failed to cancel their available timers");
        }
        AST_LIST_UNLOCK(core_instance->monitors);
}

static int cc_recalling(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        /* Both caller and callee are available, call agent's recall callback
         */
        cancel_available_timer(core_instance);
        manager_event(EVENT_FLAG_CC, "CCCallerRecalling",
                "CoreID: %d\r\n"
                "Caller: %s\r\n",
                core_instance->core_id, core_instance->agent->device_name);
        return 0;
}

static int cc_complete(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        /* Recall has made progress, call agent and monitor destructor functions
         */
        manager_event(EVENT_FLAG_CC, "CCRecallComplete",
                "CoreID: %d\r\n"
                "Caller: %s\r\n",
                core_instance->core_id, core_instance->agent->device_name);
        ao2_t_unlink(cc_core_instances, core_instance, "Unlink core instance since CC recall has completed");
        return 0;
}

static int cc_failed(struct cc_core_instance *core_instance, struct cc_state_change_args *args, enum cc_state previous_state)
{
        manager_event(EVENT_FLAG_CC, "CCFailure",
                "CoreID: %d\r\n"
                "Caller: %s\r\n"
                "Reason: %s\r\n",
                core_instance->core_id, core_instance->agent->device_name, args->debug);
        ao2_t_unlink(cc_core_instances, core_instance, "Unlink core instance since CC failed");
        return 0;
}

static int (* const state_change_funcs [])(struct cc_core_instance *, struct cc_state_change_args *, enum cc_state previous_state) = {
        [CC_AVAILABLE] = cc_available,
        [CC_CALLER_OFFERED] = cc_caller_offered,
        [CC_CALLER_REQUESTED] = cc_caller_requested,
        [CC_ACTIVE] = cc_active,
        [CC_CALLEE_READY] = cc_callee_ready,
        [CC_CALLER_BUSY] = cc_caller_busy,
        [CC_RECALLING] = cc_recalling,
        [CC_COMPLETE] = cc_complete,
        [CC_FAILED] = cc_failed,
};

static int cc_do_state_change(void *datap)
{
        struct cc_state_change_args *args = datap;
        struct cc_core_instance *core_instance;
        enum cc_state previous_state;
        int res;

        ast_log_dynamic_level(cc_logger_level, "Core %d: State change to %d requested. Reason: %s\n",
                        args->core_id, args->state, args->debug);

        core_instance = args->core_instance;

        if (!is_state_change_valid(core_instance->current_state, args->state, core_instance->agent)) {
                ast_log_dynamic_level(cc_logger_level, "Core %d: Invalid state change requested. Cannot go from %s to %s\n",
                                args->core_id, cc_state_to_string(core_instance->current_state), cc_state_to_string(args->state));
                if (args->state == CC_CALLER_REQUESTED) {
                        /*
                         * For out-of-order requests, we need to let the requester know that
                         * we can't handle the request now.
                         */
                        core_instance->agent->callbacks->respond(core_instance->agent,
                                AST_CC_AGENT_RESPONSE_FAILURE_INVALID);
                }
                ast_free(args);
                cc_unref(core_instance, "Unref core instance from when it was found earlier");
                return -1;
        }

        /* We can change to the new state now. */
        previous_state = core_instance->current_state;
        core_instance->current_state = args->state;
        res = state_change_funcs[core_instance->current_state](core_instance, args, previous_state);

        /* If state change successful then notify any device state watchers of the change */
        if (!res && !strcmp(core_instance->agent->callbacks->type, "generic")) {
                ccss_notify_device_state_change(core_instance->agent->device_name, core_instance->current_state);
        }

        ast_free(args);
        cc_unref(core_instance, "Unref since state change has completed"); /* From ao2_find */
        return res;
}

static int cc_request_state_change(enum cc_state state, const int core_id, const char *debug, va_list ap)
{
        int res;
        int debuglen;
        char dummy[1];
        va_list aq;
        struct cc_core_instance *core_instance;
        struct cc_state_change_args *args;
        /* This initial call to vsnprintf is simply to find what the
         * size of the string needs to be
         */
        va_copy(aq, ap);
        /* We add 1 to the result since vsnprintf's return does not
         * include the terminating null byte
         */
        debuglen = vsnprintf(dummy, sizeof(dummy), debug, aq) + 1;
        va_end(aq);

        if (!(args = ast_calloc(1, sizeof(*args) + debuglen))) {
                return -1;
        }

        core_instance = find_cc_core_instance(core_id);
        if (!core_instance) {
                ast_log_dynamic_level(cc_logger_level, "Core %d: Unable to find core instance.\n",
                        core_id);
                ast_free(args);
                return -1;
        }

        args->core_instance = core_instance;
        args->state = state;
        args->core_id = core_id;
        vsnprintf(args->debug, debuglen, debug, ap);

        res = ast_taskprocessor_push(cc_core_taskprocessor, cc_do_state_change, args);
        if (res) {
                cc_unref(core_instance, "Unref core instance. ast_taskprocessor_push failed");
                ast_free(args);
        }
        return res;
}

struct cc_recall_ds_data {
        int core_id;
        char ignore;
        char nested;
        struct cc_monitor_tree *interface_tree;
};

static void *cc_recall_ds_duplicate(void *data)
{
        struct cc_recall_ds_data *old_data = data;
        struct cc_recall_ds_data *new_data = ast_calloc(1, sizeof(*new_data));

        if (!new_data) {
                return NULL;
        }
        new_data->interface_tree = cc_ref(old_data->interface_tree, "Bump refcount of monitor tree for recall datastore duplicate");
        new_data->core_id = old_data->core_id;
        new_data->nested = 1;
        return new_data;
}

static void cc_recall_ds_destroy(void *data)
{
        struct cc_recall_ds_data *recall_data = data;
        recall_data->interface_tree = cc_unref(recall_data->interface_tree, "Unref recall monitor tree");
        ast_free(recall_data);
}

static struct ast_datastore_info recall_ds_info = {
        .type = "cc_recall",
        .duplicate = cc_recall_ds_duplicate,
        .destroy = cc_recall_ds_destroy,
};

int ast_setup_cc_recall_datastore(struct ast_channel *chan, const int core_id)
{
        struct ast_datastore *recall_datastore = ast_datastore_alloc(&recall_ds_info, NULL);
        struct cc_recall_ds_data *recall_data;
        struct cc_core_instance *core_instance;

        if (!recall_datastore) {
                return -1;
        }

        if (!(recall_data = ast_calloc(1, sizeof(*recall_data)))) {
                ast_datastore_free(recall_datastore);
                return -1;
        }

        if (!(core_instance = find_cc_core_instance(core_id))) {
                ast_free(recall_data);
                ast_datastore_free(recall_datastore);
                return -1;
        }

        recall_data->interface_tree = cc_ref(core_instance->monitors,
                        "Bump refcount for monitor tree for recall datastore");
        recall_data->core_id = core_id;
        recall_datastore->data = recall_data;
        recall_datastore->inheritance = DATASTORE_INHERIT_FOREVER;
        ast_channel_lock(chan);
        ast_channel_datastore_add(chan, recall_datastore);
        ast_channel_unlock(chan);
        cc_unref(core_instance, "Recall datastore set up. No need for core_instance ref");
        return 0;
}

int ast_cc_is_recall(struct ast_channel *chan, int *core_id, const char * const monitor_type)
{
        struct ast_datastore *recall_datastore;
        struct cc_recall_ds_data *recall_data;
        struct cc_monitor_tree *interface_tree;
        char device_name[AST_CHANNEL_NAME];
        struct ast_cc_monitor *device_monitor;
        int core_id_candidate;

        ast_assert(core_id != NULL);

        *core_id = -1;

        ast_channel_lock(chan);
        if (!(recall_datastore = ast_channel_datastore_find(chan, &recall_ds_info, NULL))) {
                /* Obviously not a recall if the datastore isn't present */
                ast_channel_unlock(chan);
                return 0;
        }

        recall_data = recall_datastore->data;

        if (recall_data->ignore) {
                /* Though this is a recall, the call to this particular interface is not part of the
                 * recall either because this is a call forward or because this is not the first
                 * invocation of Dial during this call
                 */
                ast_channel_unlock(chan);
                return 0;
        }

        if (!recall_data->nested) {
                /* If the nested flag is not set, then this means that
                 * the channel passed to this function is the caller making
                 * the recall. This means that we shouldn't look through
                 * the monitor tree for the channel because it shouldn't be
                 * there. However, this is a recall though, so return true.
                 */
                *core_id = recall_data->core_id;
                ast_channel_unlock(chan);
                return 1;
        }

        if (ast_strlen_zero(monitor_type)) {
                /* If someone passed a NULL or empty monitor type, then it is clear
                 * the channel they passed in was an incoming channel, and so searching
                 * the list of dialed interfaces is not going to be helpful. Just return
                 * false immediately.
                 */
                ast_channel_unlock(chan);
                return 0;
        }

        interface_tree = recall_data->interface_tree;
        ast_channel_get_device_name(chan, device_name, sizeof(device_name));
        /* We grab the value of the recall_data->core_id so that we
         * can unlock the channel before we start looking through the
         * interface list. That way we don't have to worry about a possible
         * clash between the channel lock and the monitor tree lock.
         */
        core_id_candidate = recall_data->core_id;
        ast_channel_unlock(chan);

        /*
         * Now we need to find out if the channel device name
         * is in the list of interfaces in the called tree.
         */
        AST_LIST_LOCK(interface_tree);
        AST_LIST_TRAVERSE(interface_tree, device_monitor, next) {
                if (!strcmp(device_monitor->interface->device_name, device_name) &&
                                !strcmp(device_monitor->interface->monitor_type, monitor_type)) {
                        /* BOOM! Device is in the tree! We have a winner! */
                        *core_id = core_id_candidate;
                        AST_LIST_UNLOCK(interface_tree);
                        return 1;
                }
        }
        AST_LIST_UNLOCK(interface_tree);
        return 0;
}

struct ast_cc_monitor *ast_cc_get_monitor_by_recall_core_id(const int core_id, const char * const device_name)
{
        struct cc_core_instance *core_instance = find_cc_core_instance(core_id);
        struct ast_cc_monitor *monitor_iter;

        if (!core_instance) {
                return NULL;
        }

        AST_LIST_LOCK(core_instance->monitors);
        AST_LIST_TRAVERSE(core_instance->monitors, monitor_iter, next) {