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NAME | C SYNOPSIS | DESCRIPTION | CAVEAT | DIAGNOSTICS | SEE ALSO | COLOPHON |
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PMDACONNECT(3) Library Functions Manual PMDACONNECT(3)
pmdaConnect - establish a connection between a daemon PMDA and
PMCD
#include <pcp/pmapi.h>
#include <pcp/pmda.h>
void pmdaConnect(pmdaInterface *dispatch);
cc ... -lpcp_pmda -lpcp
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 in‐
ternet 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 in‐
ternet 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).
The PMDA must be using PMDA_INTERFACE_2 or later, as specified in
the call to pmdaDaemon(3).
pmdaConnect will log the type of connection made to pmcd(1) if the
PMAPI(3) debugging option libpmda has been set in the global de‐
bugging 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.
pmcd(1), pipe(2), socket(2), PMAPI(3), PMDA(3), pmdaDaemon(3),
pmdaGetOpt(3), pmdaGetOptions(3) and pmdaInit(3).
This page is part of the PCP (Performance Co-Pilot) project. In‐
formation about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
[email protected]. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-11.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to [email protected]
Performance Co-Pilot PCP PMDACONNECT(3)
Pages that refer to this page: pmda(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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