PMDACONNECT(3)

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).