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NAME | C SYNOPSIS | DESCRIPTION | EXAMPLE | RETURN CODE | SEE ALSO | COLOPHON |
PMJSONGET(3) Library Functions Manual PMJSONGET(3)
pmjsonGet, pmjsonInit, pmjsonInitIndom - JSON performance metrics
extraction
#include <pcp/pmapi.h>
#include <pcp/pmjson.h>
typedef int (*json_get)(void *buffer, int length, void *data);
int pmjsonGet(json_metric_desc *json_metrics, int nmetrics, pmInDom
indom, json_get callback, void *data);
int pmjsonInit(int fd, json_metric_desc *json_metrics, int nmetrics);
int pmjsonInitIndom(int fd, json_metric_desc *json_metrics, int
nmetrics, pmInDom indom);
cc ... -lpcp_web
pmjsonGet performs metric value extraction from JSON strings for a
Performance Metric Domain Agent (PMDA(3)). Metrics and instances are
defined by the json_metrics parameter. The result of parsing is the
extraction of values for the requested metrics (as defined in the
json_pointer field) in the values field.
json_metrics is the array of json_metric_desc struct which contains
the json pointer to the metric data, possible flags to check the data
against, number of values (in the case of an array), pmAtomValue
where the data is stored, as well as the instance domain in the event
the PMDA has multiple instance domains. The number of elements in
the json_metrics array is indicated by the nmetrics parameter.
Interfaces for common cases are provided - pmjsonInit specifies a
call to the JSON parsing and metric value extraction functionality
where there are no instance domains (or the PMDA wishes to perform
instance domain operations itself) and where data can be read
directly from an open file descriptor. pmjsonInitIndom is similar,
but makes use of the pmdaCacheAdd(3) function where possible.
The JSON string must be provided by the callback function. This
function is passed a memory buffer of length bytes and an opaque user
data pointer which is unchanged from the original call to pmjsonGet.
The returned result must be the number of bytes written into buffer,
zero when no more data is available or less than zero on error
conditions.
indom is the instance domain to be passed to pmdaCacheAdd.
typedef struct json_metrics_desc {
char *json_pointer; /* json pointer to metric */
int flags; /* flags to check if set */
int num_values; /* number of values */
pmAtomValue values; /* metric value */
char *dom; /* instance domain */
} json_metric_desc;
The JSON Pointer syntax current follows RFC6901 in specifying a
metrics location within the JSON document.
For the sample JSON document:
{
"Name": "/clever_almeida",
"State": {
"Dead": false,
"Error": "",
"ExitCode": 0,
"FinishedAt": "2016-07-18T21:21:20.332488706Z",
"OOMKilled": false,
"Paused": false,
"Pid": 0,
"Restarting": false,
"Running": false,
"StartedAt": "2016-07-18T14:10:58.52487316Z"
}
}
A possible corresponding json_metric array would be as follows for
the Pid, Name, and metrics to indicate whether the container is
Running, Paused, or Restarting.
static json_metric_desc json_metrics[] = {
{ "State/Pid", 0, 1, {0}, ""},
{ "Name", 0, 1, {0}, ""},
{ "State/Running", CONTAINER_FLAG_RUNNING, 1, {0}, ""},
{ "State/Paused", CONTAINER_FLAG_PAUSED, 1, {0}, ""},
{ "State/Restarting", CONTAINER_FLAG_RESTARTING, 1, {0}, ""},
};
The functions return zero on success, otherwise an error code
suitable for passing to pmErrStr_r(3) is returned.
PMDA(3), pmErrStr_r(3), pmdaCacheAdd(3), http://json.org/ ,
https://tools.ietf.org/html/rfc7159 ,
https://tools.ietf.org/html/rfc6901 ,
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Performance Co-Pilot PCP PMJSONGET(3)
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