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NAME | C SYNOPSIS | CAVEAT | DESCRIPTION | NOTE | DIAGNOSTICS | SEE ALSO | COLOPHON |
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PMCONTROLLOG(3) Library Functions Manual PMCONTROLLOG(3)
__pmControlLog - enable, disable or enquire about logging of
performance metrics
#include "pmapi.h"
#include "libpcp.h"
int __pmControlLog(int fd, const pmResult *request, int control,
int state, int delta, pmResult **status);
cc ... -lpcp
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.
__pmControlLog may be used to enable or disable the archiving for
particular performance metrics, as identified by the request para‐
meter; see pmFetch(3) for an explanation of the pmResult struc‐
ture.
The application must have previously issued a call to __pmConnect‐
Logger(3) to establish a control-port connection to the
pmlogger(1) instance to whom the control request is to be direct‐
ed, and fd (the result from __pmConnectLogger(3)) identifies this
connection.
Within request, only the details of the performance metrics and
their associated instances will be used, i.e. the values of the
metrics, if any, will be ignored. request would typically be con‐
structed as the result of an earlier call to pmFetch(3). For met‐
rics with a singular value (having an instance domain of PM_IN‐
DOM_NULL) the corresponding pmValueSet should have the value one
in the numval field and PM_IN_NULL as the inst field of the single
pmValue supplied. If multiple explicit instances are to be
logged, the numval field of the pmValueSet should contain the num‐
ber of instances supplied and the inst fields of the pmValue
structures should contain specific instance identifiers (which may
not have the reserved value PM_IN_NULL).
If the numval field within any of the pmValueSet structures in re‐
quest has a value of zero, it indicates that all available in‐
stances of the metric should be used. Enumeration of the instance
domain is deferred until the logger fetches the metric prior to
writing it to the archive, rather than being performed when the
__pmControlLog request is received. This is useful for metrics
with instance domains that change over time. It is an error to
specify numval equal to zero if the corresponding metric has a
singular value (no instance domain).
There are several sorts of logging control available, namely
mandatory or advisory, as defined by the control argument, and on,
off or maybe as defined by the state argument. These different
types of control may be used to ensure that some performance met‐
rics can be guaranteed to always be in the archive, while others
may be dynamically enabled or disabled as determined by the level
and type of system activity.
The actual action to be performed is defined by the combination of
control and state as follows. If control is PM_LOG_MANDATORY and
state is PM_LOG_ON, then logging is enabled. If control is
PM_LOG_MANDATORY and state is PM_LOG_OFF, then logging is dis‐
abled. If control is PM_LOG_MANDATORY and state is PM_LOG_MAYBE,
then subsequent advisory controls will be honored. If the logging
state prior to the request was mandatory (on or off), the state is
changed to advisory off. If the logging state was already adviso‐
ry (either on or off), it remains unchanged. If control is
PM_LOG_ADVISORY and the last mandatory control for the metric was
PM_LOG_MAYBE, then logging is enabled or disabled as specified by
the state argument, i.e. PM_LOG_ON or PM_LOG_OFF. When the argu‐
ments state and control specify a request to change the logging
behavior, the argument delta defines the logging interval in mil‐
liseconds to be applied to all metrics and instances identified in
request.
The result argument status returns the current logging state for
each of the nominated performance metrics. There is a 1:1 corre‐
spondence between the elements of request and status. For metrics
in request that have pmValueSets with numval equal to zero, the
corresponding pmValueSet in result will contain a value for each
available instance at the time of the call. Each metric value in
status will have the current logging state encoded in it. The de‐
tailed outcome of the operation for each metric can be determined
by comparing these values to that requested via control, state and
delta.
Macros defined in libpcp.h may be used to extract the state and
logging interval from the returned metric values. PMLC_GET_ON re‐
turns true if logging is on, or false if it is off; PMLC_GET_MAND
returns true if logging is mandatory, or false if it is advisory;
PMLC_GET_INLOG returns true if the metric has been logged at least
once, or false otherwise; PMLC_GET_AVAIL returns true if the met‐
ric was available from its source the last time it was supposed to
be logged, or false if it was unavailable; and PMLC_GET_DELTA re‐
turns the current logging interval for the metric (in millisec‐
onds). PMLC_MAX_DELTA defines the greatest delta that can be re‐
turned in an encoded metric value.
As a special case, when control is PM_LOG_ENQUIRE, state and delta
are ignored, and status returns the current logging state of the
nominated performance metrics (this variant makes no changes to
the logging state).
If the value of the logging interval is 0, either for delta in a
request to change state to PM_LOG_ON, or encoded in the value re‐
turned from PM_LOG_ENQUIRE, then this corresponds to the special
``once only'' logging of metrics that appear once in the archive,
and are never logged again.
__pmControlLog returns zero on success.
This routine is not thread-safe as there is no serialization on
the use of the communication channel between the sending of the
request and receiving the reply. It is assumed that the caller is
single-threaded, which is true for the only current user of this
routine, namely pmlc(1).
PM_ERR_TOOSMALL
The number of metrics in request is less than one.
PM_ERR_VALUE
One or more of the pmValueSets in request had numval (the
number of instances) less than one.
EINVAL An invalid combination of control and state was specified,
or delta was negative.
pmlc(1), pmlogger(1), PMAPI(3), pmFetch(3) and __pmConnectLog‐
ger(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
pcp@groups.io. 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 man-pages@man7.org
Performance Co-Pilot PCP PMCONTROLLOG(3)
Pages that refer to this page: __pmconnectlogger(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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