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librrd - RRD library functions
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B<librrd> contains most of the functionality in B<RRDTool>. The command
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line utilities and language bindings are often just wrappers around the
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code contained in B<librrd>.
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This manual page documents the B<librrd> API.
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B<NOTE:> This document is a work in progress, and should be considered
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incomplete as long as this warning persists. For more information about
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the B<librrd> functions, always consult the source code.
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=item B<rrd_dump_cb_r(char *filename, int opt_header, rrd_output_callback_t cb, void *user)>
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In some situations it is necessary to get the output of C<rrd_dump> without
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writing it to a file or the standard output. In such cases an application
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can ask B<rrd_dump_cb_r> to call an user-defined function each time there
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is output to be stored somewhere. This can be used, to e.g. directly feed
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an XML parser with the dumped output or transfer the resulting string
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The arguments for B<rrd_dump_cb_r> are the same as for B<rrd_dump_opt_r>
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except that the output filename parameter is replaced by the user-defined
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callback function and an additional parameter for the callback function
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that is passed untouched, i.e. to store information about the callback state
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needed for the user-defined callback to function properly.
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Recent versions of B<rrd_dump_opt_r> internally use this callback mechanism
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to write their output to the file provided by the user.
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size_t rrd_dump_opt_cb_fileout(
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return fwrite(data, 1, len, (FILE *)user);
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The associated call for B<rrd_dump_cb_r> looks like
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res = rrd_dump_cb_r(filename, opt_header,
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rrd_dump_opt_cb_fileout, (void *)out_file);
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where the last parameter specifies the file handle B<rrd_dump_opt_cb_fileout>
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should write to. There's no specific condition for the callback to detect
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when it is called for the first time, nor for the last time. If you require
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this for initialization and cleanup you should do those tasks before and
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after calling B<rrd_dump_cr_r> respectively.
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=head1 UTILITY FUNCTIONS
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Generates random numbers just like random(). This further ensures that
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the random number generator is seeded exactly once per process.
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=item B<rrd_add_ptr(void ***dest, size_t *dest_size, void *src)>
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Dynamically resize the array pointed to by C<dest>. C<dest_size> is a
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pointer to the current size of C<dest>. Upon successful realloc(), the
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C<dest_size> is incremented by 1 and the C<src> pointer is stored at the
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end of the new C<dest>. Returns 1 on success, 0 on failure.
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type *elem = "whatever";
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if (!rrd_add_ptr(&arr, &arr_size, elem))
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=item B<rrd_add_strdup(char ***dest, size_t *dest_size, char *src)>
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Like C<rrd_add_ptr>, except adds a C<strdup> of the source string.
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size_t arr_size = NULL;
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char *str = "example text";
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if (!rrd_add_strdup(&arr, &arr_size, str))
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=item B<rrd_free_ptrs(void ***src, size_t *cnt)>
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Free an array of pointers allocated by C<rrd_add_ptr> or
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C<rrd_add_strdup>. Also frees the array pointer itself. On return, the
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source pointer will be NULL and the count will be zero.
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/* created as above */
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rrd_free_ptrs(&arr, &arr_size);
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/* here, arr == NULL && arr_size == 0 */
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=item B<rrd_mkdir_p(const char *pathname, mode_t mode)>
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Create the directory named C<pathname> including all of its parent
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directories (similar to C<mkdir -p> on the command line - see L<mkdir(1)> for
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more information). The argument C<mode> specifies the permissions to use. It
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is modified by the process's C<umask>. See L<mkdir(2)> for more details.
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The function returns 0 on success, a negative value else. In case of an error,
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C<errno> is set accordingly. Aside from the errors documented in L<mkdir(2)>,
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the function may fail with the following errors:
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C<pathname> is C<NULL> or the empty string.
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Insufficient memory was available.
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=item B<any error returned by L<stat(2)>>
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In contrast to L<mkdir(2)>, the function does B<not> fail if C<pathname>
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already exists and is a directory.
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RRD Contributors <rrd-developers@lists.oetiker.ch>
added
removed
doc/librrd.pod
