NAME

       pmdaConnect - establish a connection between a daemon PMDA and PMCD

C SYNOPSIS

       #include <pcp/pmapi.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) debugging
       option libpmda has been set  in  the  global  debugging  specification,  as  described  in
       pmSetDebug(3).

       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).