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PMDAMAIN

PMDAMAIN

Section: C Library Functions (3) Updated: SGI
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NAME

pmdaMain, pmdaMainLoop, pmdaSetResultCallBack, pmdaSetCheckCallBack, pmdaSetDoneCallBack, pmdaMainLoopFreeResultCallback - generic PDU processing for a PMDA  

C SYNOPSIS

#include <pcp/pmapi.h>
#include <pcp/impl.h>
#include <pcp/pmda.h>

cc ... -lpcp_pmda -lpcp

PMDA Interface 2 or higher

void pmdaMain(pmdaInterface *dispatch);

void pmdaSetResultCallBack(pmdaInterface *dispatch, pmdaResultCallBack callback);

void pmdaSetCheckCallBack(pmdaInterface *dispatch, pmdaCheckCallBack callback);

void pmdaSetDoneCallBack(pmdaInterface *dispatch, pmdaDoneCallBack callback);

PMDA Interface 1

void pmdaMainLoop(char *name, int infd, int outfd, _pmPMDA *dispatch, int (*check)(void), void (*done)(void));

void pmdaMainLoopFreeResultCallback(void (*callback)(pmResult *res));  

DESCRIPTION

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.

pmdaMainLoop and pmdaMainLoopFreeResultCallback implemented an earlier version of this functionality. Both functions will be removed in a later release and should not be used.

The arguments that are now encapsulated in pmdaExt that were passed to pmdaMainLoop include the name of the PMDA (used only in error messages) and the file descriptors infd and outfd used to receive and send PDUs to the pmcd(1) process.

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;        /* usage TBD */
    } comm;             /* set/return communication and version info */
    int status;         /* return initialization status here */

    union {
        struct {                              /* PMDA_INTERFACE_1 */
            int (*profile)(__pmProfile *);
            int (*fetch)(int, pmID *, pmResult **);
            int (*desc)(pmID, pmDesc *);
            int (*instance)(pmInDom, int, char *, __pmInResult **);
            int (*text)(int, int, char **);
            int (*control)(pmResult *, int, int, int);
            int (*store)(pmResult *);
        } one;

        struct {                              /* PMDA_INTERFACE_2 or _3 */
            pmdaExt *e_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;

        struct {                              /* PMDA_INTERFACE_4 */
            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;
    } 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_1 will force pmdaMain to use the callbacks in the version.one structure. A setting of PMDA_INTERFACE_2 or PMDA_INTERFACE_3 will force pmdaMain to use the callbacks in the version.two structure. A setting of PMDA_INTERFACE_4 will force pmdaMain to use the callbacks in the version.four 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.

pmdaMainLoop provided two additional callbacks, check and done. 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 callback done would typically be used to monitor termination conditions, or do PMDA housekeeping required after PDU processing.

These callbacks should now be set with pmdaSetCheckCallBack and pmdaSetDoneCallBack when using pmdaMain.

One further 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. The routine pmdaMainLoopFreeResultCallback has been replaced by pmdaSetResultCallBack.

pmdaMain executes as a continuous loop, returning only when an end of file is encountered on the PDU input file descriptor.  

SEE ALSO

pmcd(1), pmdbg(1), PMAPI(3) and PMDA(3).  

DIAGNOSTICS

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) debug control variable (pmdebug) has the DBG_TRACE_LIBPMDA flag set then each PDU that is received is reported in the PMDA's log file.


 

Index

NAME
C SYNOPSIS
DESCRIPTION
SEE ALSO
DIAGNOSTICS

This document was created by man2html, using the manual pages.
Time: 21:52:36 GMT, April 16, 2011