PMDALABEL(3)

NAME
pmdaLabel, pmdaSetLabelCallBack - fill pmdaLabelSet structures with metric labels

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

int pmdaLabel(int ident, int type, pmLabelSet **sets, pmdaExt *pmda);
int pmdaSetLabelCallBack(pmdaInterface *dispatch, pmdaLabelCallBack callback);

cc ... -lpcp_pmda -lpcp

DESCRIPTION
As part of the Performance Metrics Domain Agent (PMDA) API (see PMDA(3)), pmdaLabel uses the standard PMDA(3) data structures to return the labels for performance domain, instance domain, metric or individual instances in "JSONB" format in the given sets data structure.

The type argument determines the interpretation of ident and the requested form of label, as follows:

PM_LABEL_DOMAIN
    when ident is a PMDA domain identifier,

PM_LABEL_CLUSTER
    when ident is a metric identifier and labels for the cluster containing that metric are being requested.

PM_LABEL_ITEM
    when ident is a metric identifier,

PM_LABEL_INDOM
    when ident is an instance domain identifier, or

PM_LABEL_INSTANCES
    when ident is a metric identifier and labels for all instances of that metric are being requested.

The label sets pointer must be initialised to NULL before calling pmdaLabel and space is only to be allocated when labels are present and returned. In this case, the return code must indicate the number of label sets that have been allocated. This will only ever be greater than one in the PM_LABEL_INSTANCES case.

This is one of the few generic callbacks in libpcp_pmda (see PMDA(3)) that is incomplete, requiring a further pmdaLabelCallBack method of its own. The additional callback should be registered using pmdaSetLabelCallBack and the pmdaLabelCallBack method has the following prototype:
int func(pmInDom indom, unsigned int inst, pmLabelSet **set)

The purpose of the pmdaLabelCallBack routine is to return the label(s) for an individual instance inst of a given instance domain, indom. Its successful return code differs significantly to pmdaLabel, as described below.

CAVEAT
The PMDA must be using PMDA_PROTOCOL_7 or later, as specified in the call to pmdaDSO(3) or pmdaDaemon(3).

DIAGNOSTICS
On success pmdaLabel returns the number of label sets created. This is usually zero or one, except in the case of PM_LABEL_INSTANCES where more than one label sets will often be returned, one for each instance of the requested metric.

By contrast, on success of the pmdaLabelCallBack routine the number of labels successfully added to the provided labelset pointer must be returned (and not the total number of label sets).

If labels for the requested entity could not be obtained due to a catastrophic failure, such as an out of memory condition, these routines will return a negative error code.

SEE ALSO
pminfo(1), malloc(3), PMAPI(3), PMDA(3), pmdaDaemon(3), pmdaDSO(3), pmdaInit(3) and pmLookupLabels(3).