mmv_stats_registry — Initialize the Memory Mapped Value file

C Synopsis

#include <pcp/pmapi.h>
#include <pcp/mmv_stats.h>

mmv_registry_t *mmv_stats_registry(const char *file, int cluster,
                           mmv_stats_flags_t flags);

void *mmv_stats_start(mmv_registry_t *registry);
void  mmv_stats_stop(const char *fname, void *addr);

cc ... -lpcp_mmv -lpcp


mmv_stats_registry initializes an opaque structure that defines various aspects of a memory mapped file. This file is used for lightweight interprocess communication between an instrumented application and pmdammv(1).

The mmv_stats_registry interface is used to allocate a registry, and allows the name of the MMV(5) file, the cluster identifier and the flags (if any) to be set. It returns a handle that is used in subsequent MMV API calls when adding metrics, indoms, instances and labels to the registry - before actually creating the file.

mmv_stats_start is the call that creates the MMV(5) file with  the handle that returns mmv_stats_registry. It returns the mapped memory handle used in subsequent MMV API calls, such as mmv_inc_value(3).

mmv_stats_stop performs an orderly shutdown of the mapping handle returned by an earlier initialization call and also frees the registry structure.

The combination of mmv_stats_registry and mmv_stats_start  do the same as the deprecated calls mmv_stats(2)_init. However, now, one should first call mmv_stats_registry and then the API calls that add instances, indoms, metrics and labels. In this way, there is no need to know in advance which version of the MMV(1|2|3) mapping will be used as it is calculated automatically.

The file is created in the $PCP_TMP_DIR/mmv directory, the name argument is expected to be a basename of the file, not the full path. The metadata content of the file does not change after the file has been created.

The old file is removed unconditionally unless there was an error.

cluster is the preferred MMV PMDA cluster ID to be used for the metrics the originates the call mmv_stats_start. The flags provide additional control over the behaviour of the MMV PMDA - e.g. use of MMV_FLAG_PROCESS will ensure values are only exported when the instrumented application is running - this is verified on each request for new values.

The next sections explain how to add metrics, indoms, instances and labels.

Add Metrics

int mmv_stats_add_metric(mmv_registry_t *registry, const char *name, int item,
                       mmv_metric_type_t type, mmv_metric_sem_t sem, pmUnits units,
                       int serial, const char *shorthelp, const char *longhelp);

When adding a metric, internally it is being handled using the next struct. sem match in the struct is semantics. units match in the struct is dimension. serial match in the struct is indom.

        typedef struct {
            char *name;                 /* Name of the metric */
            __uint32_t item;            /* Item component of PMID */
            mmv_metric_type_t type;     /* Type of the metric */
            mmv_metric_sem_t semantics; /* Semantics of the metric */
            pmUnits dimension;          /* Dimensions (TIME,SPACE,etc) */
            __uint32_t indom;           /* Instance domain identifier */
            char *shorttext;            /* Optional, one-line help */
            char *helptext;             /* Optional, full help text */
        } mmv_metric2_t;

Add Indoms

int mmv_stats_add_indom(mmv_registry_t *registry, int serial,
                       const char *shorthelp, const char *longhelp);

When adding an indom, internally it is being handled using the next struct.

        typedef struct {
            __uint32_t serial;           /* Unique serial number */
            __uint32_t count;            /* Number of instances */
            mmv_instances2_t *instances; /* Internal/external IDs */
            char *shorttext;             /* Short help text */
            char *helptext;              /* Long help text */
        } mmv_indom2_t;

Add Instances

int mmv_stats_add_instance(mmv_registry_t *registry, int serial,
                          int instid, const char *instname);

When adding an instance, internally it is being handled using the next struct. instid match in the struct is internal while instname is external.

        typedef struct {
            __int32_t internal;
            char *external;
        } mmv_instances2_t;

It is worth mentioning that if the indom of the instance is not found it  returns an error.

Add Labels

int mmv_stats_add_registry_label(mmv_registry_t *registry,
                                const char *name, const char *value,
                                mmv_value_type_t type, int optional);

int mmv_stats_add_indom_label(mmv_registry_t *registry, int serial,
                     const char *name, const char *value,
                     mmv_value_type_t type, int optional);

int mmv_stats_add_metric_label(mmv_registry_t *registry, int item,
                      const char *name, const char *value,
                      mmv_value_type_t type, int optional);

int mmv_stats_add_instance_label(mmv_registry_t *registry, int serial,
                        int instid, const char *name, const char *value,
                        mmv_value_type_t type, int optional);

registry is the handle obtained from mmv_stats_registry. name and value are the strings that will form the label.


At the moment there is a simple check of the correctness of the value. After adding a label, it is called a function to verify if it is correct.

Additionally, if optional is set, it is added the flag PM_LABEL_OPTIONAL.

serial is the serial of the indom when adding an indom or instance label.  item is the metric identifier when adding a metric label. Finally, when  adding a registry label it is not necessary to give the cluster id because  it will be taken from the internal registry struct already created.

mmv_stats_add_registry_label adds a PM_LABEL_CLUSTER.

mmv_stats_add_indom_label adds a PM_LABEL_INDOM.

mmv_stats_add_metric_label adds a PM_LABEL_ITEM.

mmv_stats_add_instance_label adds a PM_LABEL_INSTANCES.


Return Values

When adding metrics, indoms, instances and labels, if correct returns 0
and if not it returns an errno code. The other functions return the address
of the memory mapped region on success. On failure, NULL is returned and
errno is set to a value suitable for decoding with strerror(3).

See Also

mmv_inc_value(3), mmv_lookup_value_desc(3), strerror(3) and mmv(5).

Referenced By


Performance Co-Pilot