kamailio/modules_k/usrloc

usrloc Module

Jan Janak

   FhG FOKUS

Daniel-Constantin Mierla

   <miconda@gmail.com>

Edited by

Jan Janak

Edited by

Bogdan-Andrei Iancu

   Copyright © 2003 FhG FOKUS

   Copyright © 2005 voice-system.ro
   Revision History
   Revision $Revision$ $Date$
     __________________________________________________________________

   Table of Contents

   1. Admin Guide

        1. Overview

              1.1. Contact matching

        2. Dependencies

              2.1. Kamailio Modules
              2.2. External Libraries or Applications

        3. Exported Parameters

              3.1. nat_bflag (integer)
              3.2. user_column (string)
              3.3. domain_column (string)
              3.4. contact_column (string)
              3.5. expires_column (string)
              3.6. q_column (string)
              3.7. callid_column (string)
              3.8. cseq_column (string)
              3.9. methods_column (string)
              3.10. flags_column (string)
              3.11. cflags_column (string)
              3.12. user_agent_column (string)
              3.13. received_column (string)
              3.14. socket_column (string)
              3.15. path_column (string)
              3.16. use_domain (integer)
              3.17. desc_time_order (integer)
              3.18. timer_interval (integer)
              3.19. db_url (string)
              3.20. db_mode (integer)
              3.21. matching_mode (integer)
              3.22. cseq_delay (integer)
              3.23. fetch_rows (integer)
              3.24. hash_size (integer)

        4. Exported Functions
        5. Exported MI Functions

              5.1. ul_rm
              5.2. ul_rm_contact
              5.3. ul_dump
              5.4. ul_flush
              5.5. ul_add
              5.6. ul_show_contact

        6. Exported statistics

              6.1. users
              6.2. contacts
              6.3. expires
              6.4. registered_users

   2. Developer Guide

        1. Available Functions

              1.1. ul_register_domain(name)
              1.2. ul_insert_urecord(domain, aor, rec)
              1.3. ul_delete_urecord(domain, aor)
              1.4. ul_get_urecord(domain, aor)
              1.5. ul_lock_udomain(domain)
              1.6. ul_unlock_udomain(domain)
              1.7. ul_release_urecord(record)
              1.8. ul_insert_ucontact(record, contact, expires, q, callid,
                      cseq, flags, cont, ua, sock)

              1.9. ul_delete_ucontact (record, contact)
              1.10. ul_get_ucontact(record, contact)
              1.11. ul_get_all_ucontacts (buf, len, flags)
              1.12. ul_update_ucontact(contact, expires, q, callid, cseq,
                      set, res, ua, sock)

              1.13. ul_bind_ursloc( api )
              1.14. ul_register_ulcb(type ,callback, param)
              1.15. ul_get_num_users()

   List of Examples

   1.1. Set nat_bflag parameter
   1.2. Set user_column parameter
   1.3. Set user_column parameter
   1.4. Set contact_column parameter
   1.5. Set expires_column parameter
   1.6. Set q_column parameter
   1.7. Set callid_column parameter
   1.8. Set cseq_column parameter
   1.9. Set methods_column parameter
   1.10. Set flags_column parameter
   1.11. Set cflags_column parameter
   1.12. Set user_agent_column parameter
   1.13. Set received_column parameter
   1.14. Set socket_column parameter
   1.15. Set path_column parameter
   1.16. Set use_domain parameter
   1.17. Set desc_time_order parameter
   1.18. Set timer_interval parameter
   1.19. Set db_url parameter
   1.20. Set db_mode parameter
   1.21. Set matching_mode parameter
   1.22. Set cseq_delay parameter
   1.23. Set fetch_rows parameter
   1.24. Set hash_size parameter

Chapter 1. Admin Guide

   Table of Contents

   1. Overview

        1.1. Contact matching

   2. Dependencies

        2.1. Kamailio Modules
        2.2. External Libraries or Applications

   3. Exported Parameters

        3.1. nat_bflag (integer)
        3.2. user_column (string)
        3.3. domain_column (string)
        3.4. contact_column (string)
        3.5. expires_column (string)
        3.6. q_column (string)
        3.7. callid_column (string)
        3.8. cseq_column (string)
        3.9. methods_column (string)
        3.10. flags_column (string)
        3.11. cflags_column (string)
        3.12. user_agent_column (string)
        3.13. received_column (string)
        3.14. socket_column (string)
        3.15. path_column (string)
        3.16. use_domain (integer)
        3.17. desc_time_order (integer)
        3.18. timer_interval (integer)
        3.19. db_url (string)
        3.20. db_mode (integer)
        3.21. matching_mode (integer)
        3.22. cseq_delay (integer)
        3.23. fetch_rows (integer)
        3.24. hash_size (integer)

   4. Exported Functions
   5. Exported MI Functions

        5.1. ul_rm
        5.2. ul_rm_contact
        5.3. ul_dump
        5.4. ul_flush
        5.5. ul_add
        5.6. ul_show_contact

   6. Exported statistics

        6.1. users
        6.2. contacts
        6.3. expires
        6.4. registered_users

1. Overview

   1.1. Contact matching

   User location module. The module keeps a user location table and
   provides access to the table to other modules. The module exports no
   functions that could be used directly from scripts.

1.1. Contact matching

   How the contacts are matched (dor same AOR - Address of Record) is an
   important aspect of the usrloc module, especially in the context of NAT
   traversal - this raises more problems since contacts from different
   phones of the same user may overlap (if behind NATs with same
   configuration) or the re-register contact of the same phone may be seen
   as a new one (due different binding via NAT).

   The SIP RFC 3261 publishes a matching algorithm based only on the
   contact string with callid and cseq number extra checking (if callid is
   the same, it must have a higher cseq number, otherwise it is invalid).
   But as argumented above, this is not enough in NAT traversal context,
   so the Kamailio implementation of contact matching offers more
   algorithms:
     * contact based only - it is strict RFC 3261 compliancy - the contact
       is matched as string and extra checked via callid and cseq (if
       callid is the same, it must have a higher cseq number, otherwise it
       is invalid).
     * contact and callid based - it is an extension of the first case -
       the contact and callid must be matched as string; the cseq must be
       higher than the previous one - so be careful how you deal with
       REGISTER retransmissions in this case.
     * contact and path based - it is an extension of the first case - the
       contact and path must be matched as string; the cseq must be higher
       than the previous one - so be careful how you deal with REGISTER
       retransmissions in this case.

   How to control/select the contact maching algorithm, please see the
   module parameter matching_mode at Section 3.21, “matching_mode
   (integer)”.

2. Dependencies

   2.1. Kamailio Modules
   2.2. External Libraries or Applications

2.1. Kamailio Modules

   The following modules must be loaded before this module:
     * Optionally a database module.

2.2. External Libraries or Applications

   The following libraries or applications must be installed before
   running Kamailio with this module loaded:
     * None.

3. Exported Parameters

   3.1. nat_bflag (integer)
   3.2. user_column (string)
   3.3. domain_column (string)
   3.4. contact_column (string)
   3.5. expires_column (string)
   3.6. q_column (string)
   3.7. callid_column (string)
   3.8. cseq_column (string)
   3.9. methods_column (string)
   3.10. flags_column (string)
   3.11. cflags_column (string)
   3.12. user_agent_column (string)
   3.13. received_column (string)
   3.14. socket_column (string)
   3.15. path_column (string)
   3.16. use_domain (integer)
   3.17. desc_time_order (integer)
   3.18. timer_interval (integer)
   3.19. db_url (string)
   3.20. db_mode (integer)
   3.21. matching_mode (integer)
   3.22. cseq_delay (integer)
   3.23. fetch_rows (integer)
   3.24. hash_size (integer)

3.1. nat_bflag (integer)

   The index of the branch flag to be used as NAT marker (if the contact
   is or not natted). This is a branch flag and it will be imported and
   used by all other modules depending of usrloc module.

   Default value is “not set”.

   Example 1.1. Set nat_bflag parameter
...
modparam("usrloc", "nat_bflag", 3)
...

3.2. user_column (string)

   Name of column containing usernames.

   Default value is “username”.

   Example 1.2. Set user_column parameter
...
modparam("usrloc", "user_column", "username")
...

3.3. domain_column (string)

   Name of column containing domains.

   Default value is “domain”.

   Example 1.3. Set user_column parameter
...
modparam("usrloc", "domain_column", "domain")
...

3.4. contact_column (string)

   Name of column containing contacts.

   Default value is “contact”.

   Example 1.4. Set contact_column parameter
...
modparam("usrloc", "contact_column", "contact")
...

3.5. expires_column (string)

   Name of column containing expires value.

   Default value is “expires”.

   Example 1.5. Set expires_column parameter
...
modparam("usrloc", "expires_column", "expires")
...

3.6. q_column (string)

   Name of column containing q values.

   Default value is “q”.

   Example 1.6. Set q_column parameter
...
modparam("usrloc", "q_column", "q")
...

3.7. callid_column (string)

   Name of column containing callid values.

   Default value is “callid”.

   Example 1.7. Set callid_column parameter
...
modparam("usrloc", "callid_column", "callid")
...

3.8. cseq_column (string)

   Name of column containing cseq numbers.

   Default value is “cseq”.

   Example 1.8. Set cseq_column parameter
...
modparam("usrloc", "cseq_column", "cseq")
...

3.9. methods_column (string)

   Name of column containing supported methods.

   Default value is “methods”.

   Example 1.9. Set methods_column parameter
...
modparam("usrloc", "methods_column", "methods")
...

3.10. flags_column (string)

   Name of column to save the internal flags of the record.

   Default value is “flags”.

   Example 1.10. Set flags_column parameter
...
modparam("usrloc", "flags_column", "flags")
...

3.11. cflags_column (string)

   Name of column to save the branch/contact flags of the record.

   Default value is “cflags”.

   Example 1.11. Set cflags_column parameter
...
modparam("usrloc", "cflags_column", "cflags")
...

3.12. user_agent_column (string)

   Name of column containing user-agent values.

   Default value is “user_agent”.

   Example 1.12. Set user_agent_column parameter
...
modparam("usrloc", "user_agent_column", "user_agent")
...

3.13. received_column (string)

   Name of column containing the source IP, port, and protocol from the
   REGISTER message.

   Default value is “received”.

   Example 1.13. Set received_column parameter
...
modparam("usrloc", "received_column", "received")
...

3.14. socket_column (string)

   Name of column containing the received socket information (IP:port) for
   the REGISTER message.

   Default value is “socket”.

   Example 1.14. Set socket_column parameter
...
modparam("usrloc", "socket_column", "socket")
...

3.15. path_column (string)

   Name of column containing the Path header.

   Default value is “path”.

   Example 1.15. Set path_column parameter
...
modparam("usrloc", "path_column", "path")
...

3.16. use_domain (integer)

   If the domain part of the user should be also saved and used for
   identifing the user (along with the username part). Useful in multi
   domain scenarios. Non 0 value means true.

   Default value is “0 (false)”.

   Example 1.16. Set use_domain parameter
...
modparam("usrloc", "use_domain", 1)
...

3.17. desc_time_order (integer)

   If the user's contacts should be kept timestamp ordered; otherwise the
   contact will be ordered based on q value. Non 0 value means true.

   Default value is “0 (false)”.

   Example 1.17. Set desc_time_order parameter
...
modparam("usrloc", "desc_time_order", 1)
...

3.18. timer_interval (integer)

   Number of seconds between two timer runs. The module uses timer to
   delete expired contacts, synchronize with database and other tasks,
   that need to be run periodically.

   Default value is 60.

   Example 1.18. Set timer_interval parameter
...
modparam("usrloc", "timer_interval", 120)
...

3.19. db_url (string)

   URL of the database that should be used.

   Default value is “mysql://openser:openserrw@localhost/openser”.

   Example 1.19. Set db_url parameter
...
modparam("usrloc", "db_url", "dbdriver://username:password@dbhost/dbname")
...

3.20. db_mode (integer)

   The usrloc module can utilize database for persistent contact storage.
   If you use database, your contacts will survive machine restarts or SW
   crashes. The disadvantage is that accessing database can be very time
   consuming. Therefore, usrloc module implements four database accessing
   modes:
     * 0 - This disables database completely. Only memory will be used.
       Contacts will not survive restart. Use this value if you need a
       really fast usrloc and contact persistence is not necessary or is
       provided by other means.
     * 1 - Write-Through scheme. All changes to usrloc are immediately
       reflected in database too. This is very slow, but very reliable.
       Use this scheme if speed is not your priority but need to make sure
       that no registered contacts will be lost during crash or reboot.
     * 2 - Write-Back scheme. This is a combination of previous two
       schemes. All changes are made to memory and database
       synchronization is done in the timer. The timer deletes all expired
       contacts and flushes all modified or new contacts to database. Use
       this scheme if you encounter high-load peaks and want them to
       process as fast as possible. The mode will not help at all if the
       load is high all the time. Also, latency of this mode is much lower
       than latency of mode 1, but slightly higher than latency of mode 0.
     * 3 - DB-Only scheme. No memory cache is kept, all operations being
       directly performed with the database. The timer deletes all expired
       contacts from database - cleans after clients that didn't
       un-register or re-register. The mode is useful if you configure
       more servers sharing the same DB without any replication at SIP
       level. The mode may be slower due the high number of DB operation.
       For example NAT pinging is a killer since during each ping cycle
       all nated contact are loaded from the DB; The lack of memory
       caching also disable the statistics exports.

Warning

   In case of crash or restart contacts that are in memory only and
   haven't been flushed yet will get lost. If you want minimize the risk,
   use shorter timer interval.

   Default value is 0.

   Example 1.20. Set db_mode parameter
...
modparam("usrloc", "db_mode", 2)
...

3.21. matching_mode (integer)

   What contact matching algorithm to be used. Refer to section
   Section 1.1, “Contact matching” for the description of the algorithms.

   The parameter may take the following values:
     * 0 - CONTACT ONLY based matching algorithm.
     * 1 - CONTACT and CALLID based matching algorithm.
     * 2 - CONTACT and PATH based matching algorithm. This mode is like
       mode 0 but allows for duplicate contacts from differing paths. If
       no path is available, it defaults to mode 0.

   Default value is 0 (CONTACT_ONLY).

   Example 1.21. Set matching_mode parameter
...
modparam("usrloc", "matching_mode", 1)
...

3.22. cseq_delay (integer)

   Delay (in seconds) for accepting as retransmissions register requests
   with same Call-ID and Cseq. The delay is calculated starting from the
   receiving time of the first register with that Call-ID and Cseq.

   Retransmissions within this delay interval will be accepted and replied
   as the original request, but no update will be done in location. If the
   delay is exceeded, error is reported.

   A value of 0 disable the retransmission detection.

   Default value is “20 seconds”.

   Example 1.22. Set cseq_delay parameter
...
modparam("usrloc", "cseq_delay", 5)
...

3.23. fetch_rows (integer)

   The number of the rows to be fetched at once from database when loading
   the location records. This value can be used to tune the load time at
   startup. For 1MB of private memory (default) it should be below 4000.
   The database driver must support fetch_result() capability.

   Default value is “2000”.

   Example 1.23. Set fetch_rows parameter
...
modparam("usrloc", "fetch_rows", 3000)
...

3.24. hash_size (integer)

   The number of entries of the hash table used by usrloc to store the
   location records is 2^hash_size. For hash_size=4, the number of entries
   of the hash table is 16.

   Default value is “9”.

   Example 1.24. Set hash_size parameter
...
modparam("usrloc", "hash_size", 10)
...

4. Exported Functions

   There are no exported functions that could be used in scripts.

5. Exported MI Functions

   5.1. ul_rm
   5.2. ul_rm_contact
   5.3. ul_dump
   5.4. ul_flush
   5.5. ul_add
   5.6. ul_show_contact

5.1.  ul_rm

   Deletes an entire AOR record (including its contacts).

   Parameters:
     * table name - table where the AOR is removed from (Ex: location).
     * AOR - user AOR in username[@domain] format (domain must be supplied
       only if use_domain option is on).

5.2.  ul_rm_contact

   Deletes a contact from an AOR record.

   Parameters:
     * table name - table where the AOR is removed from (Ex: location).
     * AOR - user AOR in username[@domain] format (domain must be supplied
       only if use_domain option is on).
     * contact - exact contact to be removed

5.3.  ul_dump

   Dumps the entire content of the USRLOC in memory cache

   Parameters:
     * brief - (optional, may not be present); if equals to string
       “brief”, a brief dump will be done (only AOR and contacts, with no
       other details)

5.4.  ul_flush

   Triggers the flush of USRLOC memory cache into DB.

5.5.  ul_add

   Adds a new contact for an user AOR.

   Parameters:
     * table name - table where the contact will be added (Ex: location).
     * AOR - user AOR in username[@domain] format (domain must be supplied
       only if use_domain option is on).
     * contact - contact string to be added
     * expires - expires value of the contact
     * Q - Q value of the contact
     * unused - unused attribute (kept for backword compatibility)
     * flags - internal USRLOC flags of the contact
     * cflags - per branch flags of the contact
     * methods - mask with supported requests of the contact

5.6.  ul_show_contact

   Dumps the contacts of an user AOR.

   Parameters:
     * table name - table where the AOR resides (Ex: location).
     * AOR - user AOR in username[@domain] format (domain must be supplied
       only if use_domain option is on).

6. Exported statistics

   6.1. users
   6.2. contacts
   6.3. expires
   6.4. registered_users

   Exported statistics are listed in the next sections.

6.1. users

   Number of AOR existing in the USRLOC memory cache for that domain - can
   not be resetted; this statistic will be register for each used domain
   (Ex: location).

6.2. contacts

   Number of contacts existing in the USRLOC memory cache for that domain
   - can not be resetted; this statistic will be register for each used
   domain (Ex: location).

6.3. expires

   Total number of expired contacts for that domain - can be resetted;
   this statistic will be register for each used domain (Ex: location).

6.4. registered_users

   Total number of AOR existing in the USRLOC memory cache for all domains
   - can not be resetted.

Chapter 2. Developer Guide

   Table of Contents

   1. Available Functions

        1.1. ul_register_domain(name)
        1.2. ul_insert_urecord(domain, aor, rec)
        1.3. ul_delete_urecord(domain, aor)
        1.4. ul_get_urecord(domain, aor)
        1.5. ul_lock_udomain(domain)
        1.6. ul_unlock_udomain(domain)
        1.7. ul_release_urecord(record)
        1.8. ul_insert_ucontact(record, contact, expires, q, callid, cseq,
                flags, cont, ua, sock)

        1.9. ul_delete_ucontact (record, contact)
        1.10. ul_get_ucontact(record, contact)
        1.11. ul_get_all_ucontacts (buf, len, flags)
        1.12. ul_update_ucontact(contact, expires, q, callid, cseq, set,
                res, ua, sock)

        1.13. ul_bind_ursloc( api )
        1.14. ul_register_ulcb(type ,callback, param)
        1.15. ul_get_num_users()

1. Available Functions

   1.1. ul_register_domain(name)
   1.2. ul_insert_urecord(domain, aor, rec)
   1.3. ul_delete_urecord(domain, aor)
   1.4. ul_get_urecord(domain, aor)
   1.5. ul_lock_udomain(domain)
   1.6. ul_unlock_udomain(domain)
   1.7. ul_release_urecord(record)
   1.8. ul_insert_ucontact(record, contact, expires, q, callid, cseq,
          flags, cont, ua, sock)

   1.9. ul_delete_ucontact (record, contact)
   1.10. ul_get_ucontact(record, contact)
   1.11. ul_get_all_ucontacts (buf, len, flags)
   1.12. ul_update_ucontact(contact, expires, q, callid, cseq, set, res,
          ua, sock)

   1.13. ul_bind_ursloc( api )
   1.14. ul_register_ulcb(type ,callback, param)
   1.15. ul_get_num_users()

1.1.  ul_register_domain(name)

   The function registers a new domain. Domain is just another name for
   table used in registrar. The function is called from fixups in
   registrar. It gets name of the domain as a parameter and returns
   pointer to a new domain structure. The fixup than 'fixes' the parameter
   in registrar so that it will pass the pointer instead of the name every
   time save() or lookup() is called. Some usrloc functions get the
   pointer as parameter when called. For more details see implementation
   of save function in registrar.

   Meaning of the parameters is as follows:
     * const char* name - Name of the domain (also called table) to be
       registered.

1.2.  ul_insert_urecord(domain, aor, rec)

   The function creates a new record structure and inserts it in the
   specified domain. The record is structure that contains all the
   contacts for belonging to the specified username.

   Meaning of the parameters is as follows:
     * udomain_t* domain - Pointer to domain returned by
       ul_register_udomain.

     * str* aor - Address of Record (aka username) of the new record (at
       this time the record will contain no contacts yet).

     * urecord_t** rec - The newly created record structure.

1.3.  ul_delete_urecord(domain, aor)

   The function deletes all the contacts bound with the given Address Of
   Record.

   Meaning of the parameters is as follows:
     * udomain_t* domain - Pointer to domain returned by
       ul_register_udomain.

     * str* aor - Address of record (aka username) of the record, that
       should be deleted.

1.4.  ul_get_urecord(domain, aor)

   The function returns pointer to record with given Address of Record.

   Meaning of the parameters is as follows:
     * udomain_t* domain - Pointer to domain returned by
       ul_register_udomain.

     * str* aor - Address of Record of request record.

1.5.  ul_lock_udomain(domain)

   The function lock the specified domain, it means, that no other
   processes will be able to access during the time. This prevents race
   conditions. Scope of the lock is the specified domain, that means, that
   multiple domain can be accessed simultaneously, they don't block each
   other.

   Meaning of the parameters is as follows:
     * udomain_t* domain - Domain to be locked.

1.6.  ul_unlock_udomain(domain)

   Unlock the specified domain previously locked by ul_lock_udomain.

   Meaning of the parameters is as follows:
     * udomain_t* domain - Domain to be unlocked.

1.7.  ul_release_urecord(record)

   Do some sanity checks - if all contacts have been removed, delete the
   entire record structure.

   Meaning of the parameters is as follows:
     * urecord_t* record - Record to be released.

1.8.  ul_insert_ucontact(record, contact, expires, q, callid, cseq, flags,
cont, ua, sock)

   The function inserts a new contact in the given record with specified
   parameters.

   Meaning of the parameters is as follows:
     * urecord_t* record - Record in which the contact should be inserted.
     * str* contact - Contact URI.
     * time_t expires - Expires of the contact in absolute value.
     * float q - q value of the contact.
     * str* callid - Call-ID of the REGISTER message that contained the
       contact.
     * int cseq - CSeq of the REGISTER message that contained the contact.
     * unsigned int flags - Flags to be set.
     * ucontact_t* cont - Pointer to newly created structure.
     * str* ua - User-Agent of the REGISTER message that contained the
       contact.
     * struct socket_info *sock - socket on which the REGISTER message was
       received on.

1.9.  ul_delete_ucontact (record, contact)

   The function deletes given contact from record.

   Meaning of the parameters is as follows:
     * urecord_t* record - Record from which the contact should be
       removed.

     * ucontact_t* contact - Contact to be deleted.

1.10.  ul_get_ucontact(record, contact)

   The function tries to find contact with given Contact URI and returns
   pointer to structure representing the contact.

   Meaning of the parameters is as follows:
     * urecord_t* record - Record to be searched for the contact.

     * str_t* contact - URI of the request contact.

1.11.  ul_get_all_ucontacts (buf, len, flags)

   The function retrieves all contacts of all registered users and returns
   them in the caller-supplied buffer. If the buffer is too small, the
   function returns positive value indicating how much additional space
   would be necessary to accommodate all of them. Please note that the
   positive return value should be used only as a “hint”, as there is no
   guarantee that during the time between two subsequent calls number of
   registered contacts will remain the same.

   If flag parameter is set to non-zero value then only contacts that have
   the specified flags set will be returned. It is, for example, possible
   to list only contacts that are behind NAT.

   Meaning of the parameters is as follows:
     * void* buf - Buffer for returning contacts.

     * int len - Length of the buffer.

     * unsigned int flags - Flags that must be set.

1.12.  ul_update_ucontact(contact, expires, q, callid, cseq, set, res, ua,
sock)

   The function updates contact with new values.

   Meaning of the parameters is as follows:
     * ucontact_t* contact - Contact URI.
     * time_t expires - Expires of the contact in absolute value.
     * float q - q value of the contact.
     * str* callid - Call-ID of the REGISTER message that contained the
       contact.
     * int cseq - CSeq of the REGISTER message that contained the contact.
     * unsigned int set - OR value of flags to be set.
     * unsigned int res - OR value of flags to be reset.
     * str* ua - User-Agent of the REGISTER message that contained the
       contact.
     * struct socket_info *sock - socket on which the REGISTER message was
       received on.

1.13.  ul_bind_ursloc( api )

   The function imports all functions that are exported by the USRLOC
   module. Overs for other modules which want to user the internal USRLOC
   API an easy way to load and access the functions.

   Meaning of the parameters is as follows:
     * usrloc_api_t* api - USRLOC API

1.14.  ul_register_ulcb(type ,callback, param)

   The function register with USRLOC a callback function to be called when
   some event occures inside USRLOC.

   Meaning of the parameters is as follows:
     * int types - type of event for which the callback should be called
       (see usrloc/ul_callback.h).
     * ul_cb f - callback function; see usrloc/ul_callback.h for
       prototype.
     * void *param - some parameter to be passed to the callback each time
       when it is called.

1.15.  ul_get_num_users()

   The function loops through all domains summing up the number of users.