pmdaSetLabelCallBack(3) — Linux manual page


PMDALABEL(3)              Library Functions Manual              PMDALABEL(3)

NAME         top

       pmdaLabel,  pmdaSetLabelCallBack  - fill pmdaLabelSet structures with
       metric labels

C SYNOPSIS         top

       #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         top

       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

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

           when ident is a PMDA domain identifier,

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

           when ident is a metric identifier,

           when ident is an instance domain identifier, or

           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.

DIAGNOSTICS         top

       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.

CAVEAT         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
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Performance Co-Pilot                 PCP                        PMDALABEL(3)