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.

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.

CAVEAT

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

SEE ALSO

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