devicestate.c

Go to the documentation of this file.

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2008, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 * Russell Bryant <russell@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 Device state management
 *
 * \author Mark Spencer <markster@digium.com> 
 * \author Russell Bryant <russell@digium.com>
 *
 * \arg \ref AstExtState
 */

/*! \page AstExtState Extension and device states in Asterisk
 *
 * (Note that these descriptions of device states and extension
 * states have not been updated to the way things work
 * in Asterisk 1.6.)
 *
 * Asterisk has an internal system that reports states
 * for an extension. By using the dialplan priority -1,
 * also called a \b hint, a connection can be made from an
 * extension to one or many devices. The state of the extension
 * now depends on the combined state of the devices.
 *
 * The device state is basically based on the current calls.
 * If the devicestate engine can find a call from or to the
 * device, it's in use.
 * 
 * Some channel drivers implement a callback function for 
 * a better level of reporting device states. The SIP channel
 * has a complicated system for this, which is improved 
 * by adding call limits to the configuration.
 * 
 * Functions that want to check the status of an extension
 * register themself as a \b watcher.
 * Watchers in this system can subscribe either to all extensions
 * or just a specific extensions.
 *
 * For non-device related states, there's an API called
 * devicestate providers. This is an extendible system for
 * delivering state information from outside sources or
 * functions within Asterisk. Currently we have providers
 * for app_meetme.c - the conference bridge - and call
 * parking (metermaids).
 *
 * There are manly three subscribers to extension states 
 * within Asterisk:
 * - AMI, the manager interface
 * - app_queue.c - the Queue dialplan application
 * - SIP subscriptions, a.k.a. "blinking lamps" or 
 *   "buddy lists"
 *
 * The CLI command "show hints" show last known state
 *
 * \note None of these handle user states, like an IM presence
 * system. res_jabber.c can subscribe and watch such states
 * in jabber/xmpp based systems.
 *
 * \section AstDevStateArch Architecture for devicestates
 *
 * When a channel driver or asterisk app changes state for 
 * a watched object, it alerts the core. The core queues
 * a change. When the change is processed, there's a query
 * sent to the channel driver/provider if there's a function
 * to handle that, otherwise a channel walk is issued to find
 * a channel that involves the object.
 * 
 * The changes are queued and processed by a separate thread.
 * This thread calls the watchers subscribing to status 
 * changes for the object. For manager, this results 
 * in events. For SIP, NOTIFY requests.
 *
 * - Device states
 *    \arg \ref devicestate.c 
 *    \arg \ref devicestate.h 
 *
 * \section AstExtStateArch Architecture for extension states
 * 
 * Hints are connected to extension. If an extension changes state
 * it checks the hint devices. If there is a hint, the callbacks into
 * device states are checked. The aggregated state is set for the hint
 * and reported back.
 *
 * - Extension states
 *    \arg \ref AstENUM ast_extension_states
 *    \arg \ref pbx.c 
 *    \arg \ref pbx.h 
 * - Structures
 *    - \ref ast_state_cb struct.  Callbacks for watchers
 *    - Callback ast_state_cb_type
 *    - \ref ast_hint struct.
 *    - Functions
 *    - ast_extension_state_add()
 *    - ast_extension_state_del()
 *    - ast_get_hint()
 * 
 */

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 263642 $")

#include "asterisk/_private.h"
#include "asterisk/channel.h"
#include "asterisk/utils.h"
#include "asterisk/lock.h"
#include "asterisk/linkedlists.h"
#include "asterisk/devicestate.h"
#include "asterisk/pbx.h"
#include "asterisk/app.h"
#include "asterisk/event.h"

/*! \brief Device state strings for printing */
static const char *devstatestring[][2] = {
   { /* 0 AST_DEVICE_UNKNOWN */     "Unknown",     "UNKNOWN"     }, /*!< Valid, but unknown state */
   { /* 1 AST_DEVICE_NOT_INUSE */   "Not in use",  "NOT_INUSE"   }, /*!< Not used */
   { /* 2 AST_DEVICE IN USE */      "In use",      "INUSE"       }, /*!< In use */
   { /* 3 AST_DEVICE_BUSY */        "Busy",        "BUSY"        }, /*!< Busy */
   { /* 4 AST_DEVICE_INVALID */     "Invalid",     "INVALID"     }, /*!< Invalid - not known to Asterisk */
   { /* 5 AST_DEVICE_UNAVAILABLE */ "Unavailable", "UNAVAILABLE" }, /*!< Unavailable (not registered) */
   { /* 6 AST_DEVICE_RINGING */     "Ringing",     "RINGING"     }, /*!< Ring, ring, ring */
   { /* 7 AST_DEVICE_RINGINUSE */   "Ring+Inuse",  "RINGINUSE"   }, /*!< Ring and in use */
   { /* 8 AST_DEVICE_ONHOLD */      "On Hold",      "ONHOLD"      }, /*!< On Hold */
};

/*!\brief Mapping for channel states to device states */
static const struct chan2dev {
   enum ast_channel_state chan;
   enum ast_device_state dev;
} chan2dev[] = {
   { AST_STATE_DOWN,            AST_DEVICE_NOT_INUSE },
   { AST_STATE_RESERVED,        AST_DEVICE_INUSE },
   { AST_STATE_OFFHOOK,         AST_DEVICE_INUSE },
   { AST_STATE_DIALING,         AST_DEVICE_INUSE },
   { AST_STATE_RING,            AST_DEVICE_INUSE },
   { AST_STATE_RINGING,         AST_DEVICE_RINGING },
   { AST_STATE_UP,              AST_DEVICE_INUSE },
   { AST_STATE_BUSY,            AST_DEVICE_BUSY },
   { AST_STATE_DIALING_OFFHOOK, AST_DEVICE_INUSE },
   { AST_STATE_PRERING,         AST_DEVICE_RINGING },
   { -100,                      -100 },
};

/*! \brief  A device state provider (not a channel) */
struct devstate_prov {
   char label[40];
   ast_devstate_prov_cb_type callback;
   AST_RWLIST_ENTRY(devstate_prov) list;
};

/*! \brief A list of providers */
static AST_RWLIST_HEAD_STATIC(devstate_provs, devstate_prov);

struct state_change {
   AST_LIST_ENTRY(state_change) list;
   char device[1];
};

/*! \brief The state change queue. State changes are queued
   for processing by a separate thread */
static AST_LIST_HEAD_STATIC(state_changes, state_change);

/*! \brief The device state change notification thread */
static pthread_t change_thread = AST_PTHREADT_NULL;

/*! \brief Flag for the queue */
static ast_cond_t change_pending;

struct devstate_change {
   AST_LIST_ENTRY(devstate_change) entry;
   uint32_t state;
   struct ast_eid eid;
   char device[1];
};

struct {
   pthread_t thread;
   struct ast_event_sub *event_sub;
   ast_cond_t cond;
   ast_mutex_t lock;
   AST_LIST_HEAD_NOLOCK(, devstate_change) devstate_change_q;
   unsigned int enabled:1;
} devstate_collector = {
   .thread = AST_PTHREADT_NULL,
   .enabled = 0,
};

/* Forward declarations */
static int getproviderstate(const char *provider, const char *address);

/*! \brief Find devicestate as text message for output */
const char *ast_devstate2str(enum ast_device_state devstate) 
{
   return devstatestring[devstate][0];
}

/* Deprecated interface (not prefixed with ast_) */
const char *devstate2str(enum ast_device_state devstate) 
{
   return devstatestring[devstate][0];
}

enum ast_device_state ast_state_chan2dev(enum ast_channel_state chanstate)
{
   int i;
   chanstate &= 0xFFFF;
   for (i = 0; chan2dev[i].chan != -100; i++) {
      if (chan2dev[i].chan == chanstate) {
         return chan2dev[i].dev;
      }
   }
   return AST_DEVICE_UNKNOWN;
}

/* Parseable */
const char *ast_devstate_str(enum ast_device_state state)
{
   return devstatestring[state][1];
}

enum ast_device_state ast_devstate_val(const char *val)
{
   if (!strcasecmp(val, "NOT_INUSE"))
      return AST_DEVICE_NOT_INUSE;
   else if (!strcasecmp(val, "INUSE"))
      return AST_DEVICE_INUSE;
   else if (!strcasecmp(val, "BUSY"))
      return AST_DEVICE_BUSY;
   else if (!strcasecmp(val, "INVALID"))
      return AST_DEVICE_INVALID;
   else if (!strcasecmp(val, "UNAVAILABLE"))
      return AST_DEVICE_UNAVAILABLE;
   else if (!strcasecmp(val, "RINGING"))
      return AST_DEVICE_RINGING;
   else if (!strcasecmp(val, "RINGINUSE"))
      return AST_DEVICE_RINGINUSE;
   else if (!strcasecmp(val, "ONHOLD"))
      return AST_DEVICE_ONHOLD;

   return AST_DEVICE_UNKNOWN;
}

/*! \brief Find out if device is active in a call or not 
   \note find channels with the device's name in it
   This function is only used for channels that does not implement 
   devicestate natively
*/
enum ast_device_state ast_parse_device_state(const char *device)
{
   struct ast_channel *chan;
   char match[AST_CHANNEL_NAME];
   enum ast_device_state res;

   ast_copy_string(match, device, sizeof(match)-1);
   strcat(match, "-");
   chan = ast_get_channel_by_name_prefix_locked(match, strlen(match));

   if (!chan)
      return AST_DEVICE_UNKNOWN;

   if (chan->_state == AST_STATE_RINGING)
      res = AST_DEVICE_RINGING;
   else
      res = AST_DEVICE_INUSE;
   
   ast_channel_unlock(chan);

   return res;
}

static enum ast_device_state devstate_cached(const char *device)
{
   enum ast_device_state res = AST_DEVICE_UNKNOWN;
   struct ast_event *event;

   event = ast_event_get_cached(AST_EVENT_DEVICE_STATE,
      AST_EVENT_IE_DEVICE, AST_EVENT_IE_PLTYPE_STR, device,
      AST_EVENT_IE_END);

   if (!event)
      return res;

   res = ast_event_get_ie_uint(event, AST_EVENT_IE_STATE);

   ast_event_destroy(event);

   return res;
}

/*! \brief Check device state through channel specific function or generic function */
static enum ast_device_state _ast_device_state(const char *device, int check_cache)
{
   char *buf;
   char *number;
   const struct ast_channel_tech *chan_tech;
   enum ast_device_state res;
   /*! \brief Channel driver that provides device state */
   char *tech;
   /*! \brief Another provider of device state */
   char *provider = NULL;

   /* If the last known state is cached, just return that */
   if (check_cache) {
      res = devstate_cached(device);
      if (res != AST_DEVICE_UNKNOWN) {
         return res;
      }
   }

   buf = ast_strdupa(device);
   tech = strsep(&buf, "/");
   if (!(number = buf)) {
      provider = strsep(&tech, ":");
      if (!tech) {
         return AST_DEVICE_INVALID;
      }
      /* We have a provider */
      number = tech;
      tech = NULL;
   }

   if (provider)  {
      ast_debug(3, "Checking if I can find provider for \"%s\" - number: %s\n", provider, number);
      return getproviderstate(provider, number);
   }

   ast_debug(4, "No provider found, checking channel drivers for %s - %s\n", tech, number);

   if (!(chan_tech = ast_get_channel_tech(tech)))
      return AST_DEVICE_INVALID;

   if (!(chan_tech->devicestate)) /* Does the channel driver support device state notification? */
      return ast_parse_device_state(device); /* No, try the generic function */

   res = chan_tech->devicestate(number);

   if (res != AST_DEVICE_UNKNOWN)
      return res;

   res = ast_parse_device_state(device);

   return res;
}

enum ast_device_state ast_device_state(const char *device)
{
   /* This function is called from elsewhere in the code to find out the
    * current state of a device.  Check the cache, first. */

   return _ast_device_state(device, 1);
}

/*! \brief Add device state provider */
int ast_devstate_prov_add(const char *label, ast_devstate_prov_cb_type callback)
{
   struct devstate_prov *devprov;

   if (!callback || !(devprov = ast_calloc(1, sizeof(*devprov))))
      return -1;

   devprov->callback = callback;
   ast_copy_string(devprov->label, label, sizeof(devprov->label));

   AST_RWLIST_WRLOCK(&devstate_provs);
   AST_RWLIST_INSERT_HEAD(&devstate_provs, devprov, list);
   AST_RWLIST_UNLOCK(&devstate_provs);

   return 0;
}

/*! \brief Remove device state provider */
int ast_devstate_prov_del(const char *label)
{
   struct devstate_prov *devcb;
   int res = -1;

   AST_RWLIST_WRLOCK(&devstate_provs);
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&devstate_provs, devcb, list) {
      if (!strcasecmp(devcb->label, label)) {
         AST_RWLIST_REMOVE_CURRENT(list);
         ast_free(devcb);
         res = 0;
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;
   AST_RWLIST_UNLOCK(&devstate_provs);

   return res;
}

/*! \brief Get provider device state */
static int getproviderstate(const char *provider, const char *address)
{
   struct devstate_prov *devprov;
   int res = AST_DEVICE_INVALID;

   AST_RWLIST_RDLOCK(&devstate_provs);
   AST_RWLIST_TRAVERSE(&devstate_provs, devprov, list) {
      ast_debug(5, "Checking provider %s with %s\n", devprov->label, provider);

      if (!strcasecmp(devprov->label, provider)) {
         res = devprov->callback(address);
         break;
      }
   }
   AST_RWLIST_UNLOCK(&devstate_provs);

   return res;
}

static void devstate_event(const char *device, enum ast_device_state state)
{
   struct ast_event *event;
   enum ast_event_type event_type;

   if (devstate_collector.enabled) {
      /* Distributed device state is enabled, so this state change is a change
       * for a single server, not the real state. */
      event_type = AST_EVENT_DEVICE_STATE_CHANGE;
   } else {
      event_type = AST_EVENT_DEVICE_STATE;
   }

   ast_debug(3, "device '%s' state '%d'\n", device, state);

   if (!(event = ast_event_new(event_type,
         AST_EVENT_IE_DEVICE, AST_EVENT_IE_PLTYPE_STR, device,
         AST_EVENT_IE_STATE, AST_EVENT_IE_PLTYPE_UINT, state,
         AST_EVENT_IE_END))) {
      return;
   }

   ast_event_queue_and_cache(event);
}

/*! Called by the state change thread to find out what the state is, and then
 *  to queue up the state change event */
static void do_state_change(const char *device)
{
   enum ast_device_state state;

   state = _ast_device_state(device, 0);

   ast_debug(3, "Changing state for %s - state %d (%s)\n", device, state, ast_devstate2str(state));

   devstate_event(device, state);
}

int ast_devstate_changed_literal(enum ast_device_state state, const char *device)
{
   struct state_change *change;

   /* 
    * If we know the state change (how nice of the caller of this function!)
    * then we can just generate a device state event. 
    *
    * Otherwise, we do the following:
    *   - Queue an event up to another thread that the state has changed
    *   - In the processing thread, it calls the callback provided by the
    *     device state provider (which may or may not be a channel driver)
    *     to determine the state.
    *   - If the device state provider does not know the state, or this is
    *     for a channel and the channel driver does not implement a device
    *     state callback, then we will look through the channel list to
    *     see if we can determine a state based on active calls.
    *   - Once a state has been determined, a device state event is generated.
    */

   if (state != AST_DEVICE_UNKNOWN) {
      devstate_event(device, state);
   } else if (change_thread == AST_PTHREADT_NULL || !(change = ast_calloc(1, sizeof(*change) + strlen(device)))) {
      /* we could not allocate a change struct, or */
      /* there is no background thread, so process the change now */
      do_state_change(device);
   } else {
      /* queue the change */
      strcpy(change->device, device);
      AST_LIST_LOCK(&state_changes);
      AST_LIST_INSERT_TAIL(&state_changes, change, list);
      ast_cond_signal(&change_pending);
      AST_LIST_UNLOCK(&state_changes);
   }

   return 1;
}

int ast_device_state_changed_literal(const char *dev)
{
   return ast_devstate_changed_literal(AST_DEVICE_UNKNOWN, dev);
}

int ast_devstate_changed(enum ast_device_state state, const char *fmt, ...) 
{
   char buf[AST_MAX_EXTENSION];
   va_list ap;

   va_start(ap, fmt);
   vsnprintf(buf, sizeof(buf), fmt, ap);
   va_end(ap);

   return ast_devstate_changed_literal(state, buf);
}

int ast_device_state_changed(const char *fmt, ...) 
{
   char buf[AST_MAX_EXTENSION];
   va_list ap;

   va_start(ap, fmt);
   vsnprintf(buf, sizeof(buf), fmt, ap);
   va_end(ap);

   return ast_devstate_changed_literal(AST_DEVICE_UNKNOWN, buf);
}

/*! \brief Go through the dev state change queue and update changes in the dev state thread */
static void *do_devstate_changes(void *data)
{
   struct state_change *next, *current;

   for (;;) {
      /* This basically pops off any state change entries, resets the list back to NULL, unlocks, and processes each state change */
      AST_LIST_LOCK(&state_changes);
      if (AST_LIST_EMPTY(&state_changes))
         ast_cond_wait(&change_pending, &state_changes.lock);
      next = AST_LIST_FIRST(&state_changes);
      AST_LIST_HEAD_INIT_NOLOCK(&state_changes);
      AST_LIST_UNLOCK(&state_changes);

      /* Process each state change */
      while ((current = next)) {
         next = AST_LIST_NEXT(current, list);
         do_state_change(current->device);
         ast_free(current);
      }
   }

   return NULL;
}

static void destroy_devstate_change(struct devstate_change *sc)
{
   ast_free(sc);
}

#define MAX_SERVERS 64
struct change_collection {
   struct devstate_change states[MAX_SERVERS];
   size_t num_states;
};

static void devstate_cache_cb(const struct ast_event *event, void *data)
{
   struct change_collection *collection = data;
   int i;
   const struct ast_eid *eid;

   if (collection->num_states == ARRAY_LEN(collection->states)) {
      ast_log(LOG_ERROR, "More per-server state values than we have room for (MAX_SERVERS is %d)\n",
         MAX_SERVERS);
      return;
   }

   if (!(eid = ast_event_get_ie_raw(event, AST_EVENT_IE_EID))) {
      ast_log(LOG_ERROR, "Device state change event with no EID\n");
      return;
   }

   i = collection->num_states;

   collection->states[i].state = ast_event_get_ie_uint(event, AST_EVENT_IE_STATE);
   collection->states[i].eid = *eid;

   collection->num_states++;
}

static void process_collection(const char *device, struct change_collection *collection)
{
   int i;
   struct ast_devstate_aggregate agg;
   enum ast_device_state state;
   struct ast_event *event;

   ast_devstate_aggregate_init(&agg);

   for (i = 0; i < collection->num_states; i++) {
      ast_debug(1, "Adding per-server state of '%s' for '%s'\n", 
         ast_devstate2str(collection->states[i].state), device);
      ast_devstate_aggregate_add(&agg, collection->states[i].state);
   }

   state = ast_devstate_aggregate_result(&agg);

   ast_debug(1, "Aggregate devstate result is %d\n", state);

   event = ast_event_get_cached(AST_EVENT_DEVICE_STATE,
      AST_EVENT_IE_DEVICE, AST_EVENT_IE_PLTYPE_STR, device,
      AST_EVENT_IE_END);
   
   if (event) {
      enum ast_device_state old_state;

      old_state = ast_event_get_ie_uint(event, AST_EVENT_IE_STATE);
      
      ast_event_destroy(event);

      if (state == old_state) {
         /* No change since last reported device state */
         ast_debug(1, "Aggregate state for device '%s' has not changed from '%s'\n",
            device, ast_devstate2str(state));
         return;
      }
   }

   ast_debug(1, "Aggregate state for device '%s' has changed to '%s'\n",
      device, ast_devstate2str(state));

   event = ast_event_new(AST_EVENT_DEVICE_STATE,
      AST_EVENT_IE_DEVICE, AST_EVENT_IE_PLTYPE_STR, device,
      AST_EVENT_IE_STATE, AST_EVENT_IE_PLTYPE_UINT, state,
      AST_EVENT_IE_END);

   if (!event) {
      return;
   }

   ast_event_queue_and_cache(event);
}

static void handle_devstate_change(struct devstate_change *sc)
{
   struct ast_event_sub *tmp_sub;
   struct change_collection collection = {
      .num_states = 0,
   };

   ast_debug(1, "Processing device state change for '%s'\n", sc->device);

   if (!(tmp_sub = ast_event_subscribe_new(AST_EVENT_DEVICE_STATE_CHANGE, devstate_cache_cb, &collection))) {
      ast_log(LOG_ERROR, "Failed to create subscription\n");
      return;
   }

   if (ast_event_sub_append_ie_str(tmp_sub, AST_EVENT_IE_DEVICE, sc->device)) {
      ast_log(LOG_ERROR, "Failed to append device IE\n");
      ast_event_sub_destroy(tmp_sub);
      return;
   }

   /* Populate the collection of device states from the cache */
   ast_event_dump_cache(tmp_sub);

   process_collection(sc->device, &collection);

   ast_event_sub_destroy(tmp_sub);
}

static void *run_devstate_collector(void *data)
{
   for (;;) {
      struct devstate_change *sc;

      ast_mutex_lock(&devstate_collector.lock);
      while (!(sc = AST_LIST_REMOVE_HEAD(&devstate_collector.devstate_change_q, entry)))
         ast_cond_wait(&devstate_collector.cond, &devstate_collector.lock);
      ast_mutex_unlock(&devstate_collector.lock);

      handle_devstate_change(sc);

      destroy_devstate_change(sc);
   }

   return NULL;
}

static void devstate_change_collector_cb(const struct ast_event *event, void *data)
{
   struct devstate_change *sc;
   const char *device;
   const struct ast_eid *eid;
   uint32_t state;

   device = ast_event_get_ie_str(event, AST_EVENT_IE_DEVICE);
   eid = ast_event_get_ie_raw(event, AST_EVENT_IE_EID);
   state = ast_event_get_ie_uint(event, AST_EVENT_IE_STATE);

   if (ast_strlen_zero(device) || !eid) {
      ast_log(LOG_ERROR, "Invalid device state change event received\n");
      return;
   }

   if (!(sc = ast_calloc(1, sizeof(*sc) + strlen(device))))
      return;

   strcpy(sc->device, device);
   sc->eid = *eid;
   sc->state = state;

   ast_mutex_lock(&devstate_collector.lock);
   AST_LIST_INSERT_TAIL(&devstate_collector.devstate_change_q, sc, entry);
   ast_cond_signal(&devstate_collector.cond);
   ast_mutex_unlock(&devstate_collector.lock);
}

/*! \brief Initialize the device state engine in separate thread */
int ast_device_state_engine_init(void)
{
   ast_cond_init(&change_pending, NULL);
   if (ast_pthread_create_background(&change_thread, NULL, do_devstate_changes, NULL) < 0) {
      ast_log(LOG_ERROR, "Unable to start device state change thread.\n");
      return -1;
   }

   return 0;
}

void ast_devstate_aggregate_init(struct ast_devstate_aggregate *agg)
{
   memset(agg, 0, sizeof(*agg));

   agg->all_unknown = 1;
   agg->all_unavail = 1;
   agg->all_busy = 1;
   agg->all_free = 1;
}

void ast_devstate_aggregate_add(struct ast_devstate_aggregate *agg, enum ast_device_state state)
{
   switch (state) {
   case AST_DEVICE_NOT_INUSE:
      agg->all_unknown = 0;
      agg->all_unavail = 0;
      agg->all_busy = 0;
      break;
   case AST_DEVICE_INUSE:
      agg->in_use = 1;
      agg->all_unavail = 0;
      agg->all_free = 0;
      agg->all_unknown = 0;
      break;
   case AST_DEVICE_RINGING:
      agg->ring = 1;
      agg->all_unavail = 0;
      agg->all_free = 0;
      agg->all_unknown = 0;
      break;
   case AST_DEVICE_RINGINUSE:
      agg->in_use = 1;
      agg->ring = 1;
      agg->all_unavail = 0;
      agg->all_free = 0;
      agg->all_unknown = 0;
      break;
   case AST_DEVICE_ONHOLD:
      agg->all_unknown = 0;
      agg->all_unavail = 0;
      agg->all_free = 0;
      agg->on_hold = 1;
      break;
   case AST_DEVICE_BUSY:
      agg->all_unknown = 0;
      agg->all_unavail = 0;
      agg->all_free = 0;
      agg->busy = 1;
      agg->in_use = 1;
      break;
   case AST_DEVICE_UNAVAILABLE:
      agg->all_unknown = 0;
   case AST_DEVICE_INVALID:
      agg->all_busy = 0;
      agg->all_free = 0;
      break;
   case AST_DEVICE_UNKNOWN:
      agg->all_busy = 0;
      agg->all_free = 0;
      break;
   case AST_DEVICE_TOTAL: /* not a device state, included for completeness. */
      break;
   }
}


enum ast_device_state ast_devstate_aggregate_result(struct ast_devstate_aggregate *agg)
{
   if (agg->all_free)
      return AST_DEVICE_NOT_INUSE;
   if ((agg->in_use || agg->on_hold) && agg->ring)
      return AST_DEVICE_RINGINUSE;
   if (agg->ring)
      return AST_DEVICE_RINGING;
   if (agg->busy)
      return AST_DEVICE_BUSY;
   if (agg->in_use)
      return AST_DEVICE_INUSE;
   if (agg->on_hold)
      return AST_DEVICE_ONHOLD;
   if (agg->all_busy)
      return AST_DEVICE_BUSY;
   if (agg->all_unknown)
      return AST_DEVICE_UNKNOWN;
   if (agg->all_unavail)
      return AST_DEVICE_UNAVAILABLE;

   return AST_DEVICE_NOT_INUSE;
}

int ast_enable_distributed_devstate(void)
{
   if (devstate_collector.enabled) {
      return 0;
   }

   devstate_collector.event_sub = ast_event_subscribe(AST_EVENT_DEVICE_STATE_CHANGE,
      devstate_change_collector_cb, NULL, AST_EVENT_IE_END);

   if (!devstate_collector.event_sub) {
      ast_log(LOG_ERROR, "Failed to create subscription for the device state change collector\n");
      return -1;
   }

   ast_mutex_init(&devstate_collector.lock);
   ast_cond_init(&devstate_collector.cond, NULL);
   if (ast_pthread_create_background(&devstate_collector.thread, NULL, run_devstate_collector, NULL) < 0) {
      ast_log(LOG_ERROR, "Unable to start device state collector thread.\n");
      return -1;
   }

   devstate_collector.enabled = 1;

   return 0;
}