NAME

       librrd - RRD library functions

DESCRIPTION

       librrd contains most of the functionality in RRDTool.  The command line utilities and
       language bindings are often just wrappers around the code contained in librrd.

       This manual page documents the librrd API.

       NOTE: This document is a work in progress, and should be considered incomplete as long as
       this warning persists.  For more information about the librrd functions, always consult
       the source code.

CORE FUNCTIONS

       rrd_dump_cb_r(char *filename, int opt_header, rrd_output_callback_t cb, void *user)
           In some situations it is necessary to get the output of "rrd_dump" without writing it
           to a file or the standard output. In such cases an application can ask rrd_dump_cb_r
           to call an user-defined function each time there is output to be stored somewhere.
           This can be used, to e.g. directly feed an XML parser with the dumped output or
           transfer the resulting string in memory.

           The arguments for rrd_dump_cb_r are the same as for rrd_dump_opt_r except that the
           output filename parameter is replaced by the user-defined callback function and an
           additional parameter for the callback function that is passed untouched, i.e. to store
           information about the callback state needed for the user-defined callback to function
           properly.

           Recent versions of rrd_dump_opt_r internally use this callback mechanism to write
           their output to the file provided by the user.

               size_t rrd_dump_opt_cb_fileout(
                   const void *data,
                   size_t len,
                   void *user)
               {
                   return fwrite(data, 1, len, (FILE *)user);
               }

           The associated call for rrd_dump_cb_r looks like

               res = rrd_dump_cb_r(filename, opt_header,
                   rrd_dump_opt_cb_fileout, (void *)out_file);

           where the last parameter specifies the file handle rrd_dump_opt_cb_fileout should
           write to. There's no specific condition for the callback to detect when it is called
           for the first time, nor for the last time. If you require this for initialization and
           cleanup you should do those tasks before and after calling rrd_dump_cr_r respectively.

       rrd_fetch_cb_register(rrd_fetch_cb_t c)
           If your data does not reside in rrd files, but you would like to draw charts using the
           rrd_graph functionality, you can supply your own rrd_fetch function and register it
           using the rrd_fetch_cb_register function.

           The argument signature and api must be the same of the callback function must be
           aequivalent to the on of rrd_fetch_fn in rrd_fetch.c.

           To activate the callback function you can use the pseudo filename cb//free_form_text.

           Note that rrdtool graph will not ask the same rrd for data twice. It determines this
           by building a key out of the values supplied to the fetch function. If the values are
           the same, the previous answer will be used.

UTILITY FUNCTIONS

       rrd_random()
           Generates random numbers just like random().  This further ensures that the random
           number generator is seeded exactly once per process.

       rrd_strtodbl
           an rrd aware string to double converter which sets rrd_error in if there is a problem
           and uses the return code exclusively for conversion status reporting.

       rrd_strtod
           works like normal strtod, but it is locale independent (and thread safe)

       rrd_snprintf
           works  like normal snprintf but it is locale independent (and thread safe)

       rrd_add_ptr(void ***dest, size_t *dest_size, void *src)
           Dynamically resize the array pointed to by "dest".  "dest_size" is a pointer to the
           current size of "dest".  Upon successful realloc(), the "dest_size" is incremented by
           1 and the "src" pointer is stored at the end of the new "dest".  Returns 1 on success,
           0 on failure.

               type **arr = NULL;
               type *elem = "whatever";
               size_t arr_size = 0;
               if (!rrd_add_ptr(&arr, &arr_size, elem))
                   handle_failure();

       rrd_add_ptr_chunk(void ***dest, size_t *dest_size, void *src, size_t *alloc, size_t chunk)
           Like "rrd_add_ptr", except the destination is allocated in chunks of "chunk".  "alloc"
           points to the number of entries allocated, whereas "dest_size" points to the number of
           valid pointers.  If more pointers are needed, "chunk" pointers are allocated and
           "alloc" is increased accordingly.  "alloc" must be >= "dest_size".

           This method improves performance on hosts with expensive "realloc()".

       rrd_add_strdup(char ***dest, size_t *dest_size, char *src)
           Like "rrd_add_ptr", except adds a "strdup" of the source string.

               char **arr = NULL;
               size_t arr_size = NULL;
               char *str  = "example text";
               if (!rrd_add_strdup(&arr, &arr_size, str))
                   handle_failure();

       rrd_add_strdup_chunk(char ***dest, size_t *dest_size, char *src, size_t *alloc, size_t
       chunk)
           Like "rrd_add_strdup", except the destination is allocated in chunks of "chunk".
           "alloc" points to the number of entries allocated, whereas "dest_size" points to the
           number of valid pointers.  If more pointers are needed, "chunk" pointers are allocated
           and "alloc" is increased accordingly.  "alloc" must be >= "dest_size".

       rrd_free_ptrs(void ***src, size_t *cnt)
           Free an array of pointers allocated by "rrd_add_ptr" or "rrd_add_strdup".  Also frees
           the array pointer itself.  On return, the source pointer will be NULL and the count
           will be zero.

               /* created as above */
               rrd_free_ptrs(&arr, &arr_size);
               /* here, arr == NULL && arr_size == 0 */

       rrd_mkdir_p(const char *pathname, mode_t mode)
           Create the directory named "pathname" including all of its parent directories (similar
           to "mkdir -p" on the command line - see mkdir(1) for more information). The argument
           "mode" specifies the permissions to use. It is modified by the process's "umask". See
           mkdir(2) for more details.

           The function returns 0 on success, a negative value else. In case of an error, "errno"
           is set accordingly. Aside from the errors documented in mkdir(2), the function may
           fail with the following errors:

           EINVAL
               "pathname" is "NULL" or the empty string.

           ENOMEM
               Insufficient memory was available.

           any error returned by stat(2)

           In contrast to mkdir(2), the function does not fail if "pathname" already exists and
           is a directory.

       rrd_scaled_duration (const char * token, unsigned long divisor, unsigned long * valuep)
           Parse a token in a context where it contains a count (of seconds or PDP instances), or
           a duration that can be converted to a count by representing the duration in seconds
           and dividing by some scaling factor.  For example, if a user would natively express a
           3 day archive of samples collected every 2 minutes, the sample interval can be
           represented by "2m" instead of 120, and the archive duration by "3d" (to be divided by
           120) instead of 2160 (3*24*60*60 / 120).  See more examples in "STEP, HEARTBEAT, and
           Rows As Durations" in rrdcreate.

           "token" must be a number with an optional single-character suffix encoding the scaling
           factor:

           "s" indicates seconds

           "m" indicates minutes.  The value is multipled by 60.

           "h" indicates hours.  The value is multipled by 3600 (or "60m").

           "d" indicates days.  The value is multipled by 86400 (or "24h").

           "w" indicates weeks.  The value is multipled by 604800 (or "7d").

           "M" indicates months.  The value is multipled by 2678400 (or "31d").  (Note this
               factor accommodates the maximum number of days in a month.)

           "y" indicates years.  The value is multipled by 31622400 (or "366d").  (Note this
               factor accommodates leap years.)

           "divisor" is a positive value representing the duration in seconds of an interval that
           the desired result counts.

           "valuep" is a pointer to where the decoded value will be stored if the conversion is
           successful.

           The initial characters of "token" must be the base-10 representation of a positive
           integer, or the conversion fails.

           If the remainder "token" is empty (no suffix), it is a count and no scaling is
           performed.

           If "token" has one of the suffixes above, the count is multipled to convert it to a
           duration in seconds.  The resulting number of seconds is divided by "divisor" to
           produce a count of intervals each of duration "divisor" seconds.  If division would
           produce a remainder (e.g., "5m" (300 seconds) divided by "90s"), the conversion is
           invalid.

           If "token" has unrecognized trailing characters the conversion fails.

           The function returns a null pointer if the conversion was successful and "valuep" has
           been updated to the scaled value.  On failure, it returns a text diagnostic suitable
           for use in user error messages.

AUTHOR

       RRD Contributors <rrd-developers@lists.oetiker.ch>