NAME¶

pmdaChildren - translate a PMID to a set of dynamic performance metric names

C SYNOPSIS¶

#include <pcp/pmapi.h>
#include <pcp/pmda.h>

int pmdaChildren(char *name, int traverse, char ***offspring, int **status, pmdaExt *pmda);

cc ... -lpcp_pmda -lpcp

DESCRIPTION¶

As part of the Performance Metrics Domain Agent (PMDA) API (see PMDA(3)), pmdaChildren is the generic callback for returning dynamic metric names (and their status) that are descendants of name.

Because implementing dynamic performance metrics requires specific PMDA support, and the facility is an optional component of a PMDA (most PMDAs do not support dynamic performance metrics), pmdaChildren is a skeleton implementation that returns PM_ERR_NAME.

A PMDA that supports dynamic performance metrics will provide a private callback that replaces pmdaChildren (by assignment to version.four.children of the pmdaInterface structure) and takes the initial metric name and returns names via offspring[] and the leaf or non-leaf status of each via status[].

If traverse is 0, then the behaviour is akin to pmGetChildren(3) and offspring[] contains the relative name component for the immediate descendants of name.

If traverse is 1, then the behaviour is akin to pmTraversePMNS(3) and offspring[] contains the absolute names of all dynamic metrics that are decedents of name.

The resulting list of pointers offspring and the string values (the names) that the pointers reference will have been allocated by pmdaChildren with a single call to malloc(3), and the caller of pmdaChildren will call free(offspring) to release the space when it is no longer required. The same holds true for the status array, namely the caller of pmdaChildren will call free(status) to release the space when it is no longer required.

CAVEAT¶

The PMDA must be using PMDA_INTERFACE_4 or later, as specified in the call to pmdaDSO(3) or pmdaDaemon(3).

DIAGNOSTICS¶

pmdaChildren returns PM_ERR_NAME if the name is not recognized or cannot be translated, otherwise the number of descendent metric names found.

SEE ALSO¶

PMAPI(3), PMDA(3), pmdaDaemon(3), pmdaDSO(3), pmdaMain(3), pmGetChildren(3) and pmTraversePMNS(3).