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NAME | C SYNOPSIS | DESCRIPTION | CALLBACKS | DIAGNOSTICS | SEE ALSO | COLOPHON |
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PMDAMAIN(3) Library Functions Manual PMDAMAIN(3)
pmdaMain, pmdaGetContext, pmdaSetResultCallBack, pmdaSetCheckCall‐
Back, pmdaSetDoneCallBack, pmdaSetEndContextCallBack - generic PDU
processing for a PMDA
#include <pcp/pmapi.h>
#include <pcp/pmda.h>
cc ... -lpcp_pmda -lpcp
void pmdaMain(pmdaInterface *dispatch);
void pmdaSetCheckCallBack(pmdaInterface *dispatch,
pmdaCheckCallBack callback);
void pmdaSetDoneCallBack(pmdaInterface *dispatch,
pmdaDoneCallBack callback);
void pmdaSetResultCallBack(pmdaInterface *dispatch,
pmdaResultCallBack callback);
void pmdaSetEndContextCallBack(pmdaInterface *dispatch,
pmdaEndContextCallBack callback);
int pmdaGetContext(void);
For Performance Metric Domain Agents (PMDA(3)) using the binary PDU
protocols to communicate with pmcd(1), the routine pmdaMain provides
a generic implementation of the PDU-driven main loop.
dispatch describes how to process each incoming PDU. It is a vector
of function pointers, one per request PDU type, as used in the DSO
interface for a PMDA, namely:
/*
* Interface Definitions for PMDA Methods
*/
typedef struct {
int domain; /* set/return performance metrics domain id here */
struct {
unsigned int pmda_interface: 8; /* PMDA DSO interface version */
unsigned int pmapi_version : 8; /* PMAPI version */
unsigned int flags : 16; /* optional feature flags */
} comm; /* set/return communication and version info */
int status; /* return initialization status here */
union {
struct { /* PMDA_INTERFACE_2 or _3 */
pmdaExt *ext;
int (*profile)(pmProfile *, pmdaExt *);
int (*fetch)(int, pmID *, pmResult **, pmdaExt *);
int (*desc)(pmID, pmDesc *, pmdaExt *);
int (*instance)(pmInDom, int, char *, pmInResult **, pmdaExt *);
int (*text)(int, int, char **, pmdaExt *);
int (*store)(pmResult *, pmdaExt *);
} two, three;
struct { /* PMDA_INTERFACE_4 or _5 */
pmdaExt *ext;
int (*profile)(pmProfile *, pmdaExt *);
int (*fetch)(int, pmID *, pmResult **, pmdaExt *);
int (*desc)(pmID, pmDesc *, pmdaExt *);
int (*instance)(pmInDom, int, char *, pmInResult **, pmdaExt *);
int (*text)(int, int, char **, pmdaExt *);
int (*store)(pmResult *, pmdaExt *);
int (*pmid)(char *, pmID *, pmdaExt *);
int (*name)(pmID, char ***, pmdaExt *);
int (*children)(char *, int, char ***, int **, pmdaExt *);
} four, five;
struct { /* PMDA_INTERFACE_6 */
pmdaExt *ext;
int (*profile)(pmProfile *, pmdaExt *);
int (*fetch)(int, pmID *, pmResult **, pmdaExt *);
int (*desc)(pmID, pmDesc *, pmdaExt *);
int (*instance)(pmInDom, int, char *, pmInResult **, pmdaExt *);
int (*text)(int, int, char **, pmdaExt *);
int (*store)(pmResult *, pmdaExt *);
int (*pmid)(char *, pmID *, pmdaExt *);
int (*name)(pmID, char ***, pmdaExt *);
int (*children)(char *, int, char ***, int **, pmdaExt *);
int (*attribute)(int, int, const char *, int, pmdaExt *);
} six;
} version;
} pmdaInterface;
This structure has been extended to incorporate the multiple
interface versions that have evolved over time. For pmdaMain,
dispatch->domain and dispatch->status are ignored. The
comm.pmda_interface field is used to determine the interface used by
the PMDA. Setting this field to PMDA_INTERFACE_2 or PMDA_INTERFACE_3
will force pmdaMain to use the callbacks in the version.two or
version.three structure. A setting of PMDA_INTERFACE_4 or
PMDA_INTERFACE_5 will force pmdaMain to use the callbacks in the
version.four or version.five structure, and similarly a
PMDA_INTERFACE_6 setting forces pmdaMain to use the callbacks in the
version.six structure. Any other value will result in an error and
termination of pmdaMain.
Note that the use of dispatch as the interface between the pmcd(1)
and the methods of the PMDA allows each PMDA to be implemented as
though it were a DSO, with pmdaMain providing a convenient wrapper
that may be used to convert from the DSO interface to the binary PDU
(daemon PMDA) interface.
pmdaMain executes as a continuous loop, returning only when an end of
file is encountered on the PDU input file descriptor.
In addition to the individual PDU processing callbacks -
pmdaProfile(3), pmdaFetch(3), pmdaDesc(3), pmdaInstance(3),
pmdaText(3), pmdaStore(3), pmdaPMID(3), pmdaName(3), pmdaChildren(3),
and pmdaAttribute(3) there are other callbacks that can affect or
inform all PDU processing within a PMDA, namely check, done and end.
These callbacks should be set with pmdaSetCheckCallBack,
pmdaSetDoneCallBack and pmdaSetEndContextCallBack.
If not null, check is called after each PDU is received (but before
it was processed), and done is called after each PDU is sent. If
check returns a value less than zero (typically PM_ERR_AGAIN), the
PDU processing is skipped and in most cases the function value is
returned as an error PDU to pmcd(1) - this may be used for PMDAs that
require some sort of deferred connection or reconnect protocols for
the underlying sources of performance metrics, e.g. a DBMS. The
error indication from check is not passed back to pmcd(1) in the
cases where no acknowledgment is expected, e.g. for a PDU_PROFILE.
The end callback allows a PMDA to keep track of state for individual
clients that are requesting it to perform actions (PDU processing).
Using pmdaGetContext a PMDA can determine, at any point, an integer
identifier that uniquely identifies the client tools at the remote
end of PMCD (for local context modes, this identifier is always
zero). This becomes very important for handling event metrics, where
each event must be propagated once only to each interested client.
It also underlies the mechanism whereby connection information is
passed to the PMDA, such as the the credentials (user and group
identifiers) for the client tool.
One final callback mechanism is provided for handling the pmResult
built for a PDU_RESULT in response to a PDU_FETCH request. By
default, pmdaMain will free the pmResult once the result has been
sent to the pmcd(1). For some PMDAs this is inappropriate, e.g. the
pmResult is statically allocated, or contains a hybrid of pinned PDU
buffer information and dynamically allocated information.
pmdaSetResultCallback may be used to define an alternative callback
from pmdaMain.
These messages may be appended to the PMDA's log file:
PMDA interface version interface not supported
The interface version is not supported by
pmdaMain.
Unrecognized pdu type The PMDA received a PDU from pmcd that it
does not recognize. This may indicate that
the pmcd process is using a more advanced
interface than pmdaMain.
If the PMAPI(3) debugging control options have the ``libpmda'' option
set then each PDU that is received is reported in the PMDA's log
file.
pmcd(1), PMAPI(3), PMDA(3), pmdaProfile(3), pmdaFetch(3),
pmdaDesc(3), pmdaInstance(3), pmdaText(3), pmdaStore(3), pmdaPMID(3),
pmdaName(3), pmdaChildren(3), and pmdaAttribute(3).
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
pcp@groups.io. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-02.) 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 PMDAMAIN(3)
Pages that refer to this page: pmda(3), pmdaattribute(3), pmdachildren(3), pmdaeventclient(3), pmdaname(3), pmdapmid(3)
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