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pmdaconnect(3)

NAME

   pmdaConnect - establish a connection between a daemon PMDA and PMCD

C SYNOPSIS

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

   void pmdaConnect(pmdaInterface *dispatch);

   cc ... -lpcp_pmda -lpcp

DESCRIPTION

   pmdaConnect  initializes  an  IPC  channel  between  a  PMDA(3) and the
   pmcd(1) process on the local host.   The  type  of  the  connection  is
   dependent on the e_io field of the pmdaExt structure:

   pmdaPipe       Use  stdin/stdout to communicate; assumes this is a pipe
                  created by pmcd before the PMDA(3) was launched.

   pmdaInet       Assume pmcd(1) will establish a connection  to  an  IPv4
                  internet  domain socket set up by the PMDA(3).  The name
                  or  number  of  the  port  must  be  specified  in   the
                  e_sockname  or  e_port  fields of the pmdaExt structure,
                  respectively.

   pmdaIPv6       Assume pmcd(1) will establish a connection  to  an  IPv6
                  internet  domain socket set up by the PMDA(3).  The name
                  or  number  of  the  port  must  be  specified  in   the
                  e_sockname  or  e_port  fields of the pmdaExt structure,
                  respectively.

   pmdaUnix       Assume pmcd(1) will establish a  connection  to  a  unix
                  domain  socket  set  up by the PMDA(3).  The port number
                  must be specified in the e_port  field  of  the  pmdaExt
                  structure.

   pmdaUnknown    The  initial  value  of  e_io  which  defaults  to using
                  stdin/stdout.

   The relevant pmdaExt fields are initialized by pmdaDaemon(3) and set by
   pmdaGetOpt(3)  or  pmdaGetOptions(3)  so  most PMDAs should not need to
   access or modify them.

   Traditionally  most  PMDAs  have  called  pmdaConnect  after  calls  to
   pmdaDaemon(3),  pmdaGetOptions(3)  (or  pmdaGetOpt(3)) and pmdaInit(3).
   If the PMDA requires significant processing at startup to identify  the
   available  metrics  and/or  instance  domains before pmdaInit(3) can be
   called, then it risks timing out during  the  handshake  protocol  that
   starts as soon as pmcd(1) launches the PMDA and does not conclude until
   pmdaConnect is called.  In this case,  it  is  advisable  to  move  the
   pmdaConnect  call, so that it comes after the call to pmdaGetOptions(3)
   (or pmdaGetOpt(3)) and before the call to pmdaInit(3).

DIAGNOSTICS

   pmdaConnect will log the type of connection  made  to  pmcd(1)  if  the
   PMAPI(3)  debug  control  variable  (pmDebug) has the DBG_TRACE_LIBPMDA
   flag set.

   If an error occurs that is unrecoverable, dispatch->status is set to  a
   value less than 0, otherwise it is zero or positive.

CAVEAT

   The  PMDA  must be using PMDA_INTERFACE_2 or later, as specified in the
   call to pmdaDaemon(3).

SEE ALSO

   pmcd(1),  pipe(2),   socket(2),   PMAPI(3),   PMDA(3),   pmdaDaemon(3),
   pmdaGetOpt(3), pmdaGetOptions(3) and pmdaInit(3).



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