введение в библиотеку поддержки агента домена Performance Metrics (introduction to the Performance Metrics Domain Agent support library)
COMMUNICATING WITH PMCD
Two approaches may be used for connecting a PMDA to a pmcd(1)
process. A Dynamic Shared Object (DSO) can be attached by
pmcd(1) using dlopen(3) when the pmcd(1) process is started. A
procedural interface referenced through a shared data structure
is used to handle requests from pmcd(1) to the PMDA .
The preferred approach is for a separate process (daemon) to
communicate with pmcd(1) using the Performance Data Units (PDU)
Inter-Process Communication (IPC) protocol.
All PMDAs are launched and controlled by the pmcd(1) process on
the local host. The requests from the clients are received by
pmcd(1) and forwarded to the appropriate PMDAs. Responses, when
required, are returned through pmcd(1) to the clients. The
requests (PDUs) that may be sent to a PMDA from pmcd(1) are
PDU_FETCH, PDU_PROFILE, PDU_INSTANCE_REQ, PDU_DESC_REQ,
PDU_TEXT_REQ and PDU_RESULT. If the PMDA implements any dynamic
metrics it may also receive PDU_PMNS_CHILD, PDU_PMNS_IDS,
PDU_PMNS_NAMES and PDU_PMNS_TRAVERSE PDUs.
