This documentation is intended for internal Performance Co-Pilot
(PCP) developer use.
These interfaces are not part of the PCP APIs that are guaranteed
to remain fixed across releases, and they may not work, or may
provide different semantics at some point in the future.
PCP contexts of type PM_CONTEXT_LOCAL are used by clients that
wish to fetch metrics directly from one or more PMDAs on the
local host without involving pmcd(1). A PMDA that is to be used
in this way must have been built as a Dynamic Shared Object
Historically the table of PMDAs available for use with
PM_CONTEXT_LOCAL was hardcoded to the following:
* The PMDA (or PMDAs) that export the operating system
performance data and data about process activity.
* The mmv PMDA.
* The sample PMDA provided $PCP_LITE_SAMPLE or $PMDA_LOCAL_SAMPLE
is set in the environment - used mostly for QA and testing.
The initial table of PMDAs available for use with
PM_CONTEXT_LOCAL is now generated dynamically from all those
PMDAs that have been installed as DSOs on the local host. The
one exception is the ``pmcd'' PMDA which only operates correctly
in the address space of a running pmcd(1) process and so is not
available to an application using a PM_CONTEXT_LOCAL context.
__pmLocalPMDA provides a number of services to amend the table of
PMDAs available for use with PM_CONTEXT_LOCAL.
The op argument specifies the what should be done and takes one
of the following values and actions:
PM_LOCAL_ADD Append an entry to the table for the PMDA with a
Performance Metrics Domain (PMD) of domain, the
path to the DSO PMDA is given by path and the
PMDA's initialization routine is init.
PM_LOCAL_DEL Removes all entries in the table where the domain
matches, or the path matches. Setting the
arguments domain to -1 or path to NULL to force
matching on the other argument. The init
argument is ignored.
PM_LOCAL_CLEAR Remove all entries from the table. All the other
arguments are ignored in this case.
The domain, name and init arguments have similar syntax and
semantics to the associated fields in the pmcd(1) configuration
file. The one difference is the path argument which is used by
__pmLocalPMDA to find a likely looking DSO by searching in this
order: $PCP_PMDAS_DIR/path, path, $PCP_PMDAS_DIR/path.dso-suffix
and finally path.dso-suffix (dso-suffix is the local platform
specific default file name suffix for a DSO, e.g. so for Linux,
dylib for Mac OS X, dll for Windows, etc.).
In most cases, __pmLocalPMDA returns 0 to indicate success. If
op is invalid, then the return value is PM_ERR_CONV else if there
is no matching table entry found for a PM_LOCAL_DEL operation,
PM_ERR_INDOM is returned.
This page is part of the PCP (Performance Co-Pilot) project.
Information 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@example.com. This page was obtained from the
project's upstream Git repository
⟨https://github.com/performancecopilot/pcp.git⟩ on 2020-12-18.
(At that time, the date of the most recent commit that was found
in the repository was 2020-12-18.) 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
Performance Co-Pilot PMLOCALPMDA(3)