int pmdaAttribute(int context, int key, char *value, int length, pmdaExt *pmda);
cc ... -lpcp_pmda -lpcp
As part of the Performance Metrics Domain Agent (PMDA) API (see PMDA(3)), pmdaAttribute is the generic callback for responding to client connection attributes. These attributes include client credential information, such as user ID and group ID.
A PMDA that supports connection attributes will provide a private pmdaAttribute callback by assignment to version.six.attribute of the pmdaInterface structure, and implement custom logic for any of the attribute key-value pairs of interest to it.
All attributes are associated with a specific client context, and these can be uniquely identified using the ctx first argument. The PMDA should track client connections, and disconnections using the pmdaSetEndContextCallBack(3) interface, as a result. The pmdaGetContext(3) interface may be particularly helpful also.
All attributes are passed as key-value pairs and the value is always passed as a null-terminated string of given length. This includes numeric attributes like the user ID.
The most commonly used attributes would be PCP_ATTR_USERID and PCP_ATTR_GROUPID but others may also be optionally passed (such as PCP_ATTR_USERNAME) if they are available. Some attributes will be consumed by pmcd and never through passed to PMDAs, such as PCP_ATTR_PASSWORD. A complete list of all possible attributes can be found in the headers listed above, all are prefixed by PCP_ATTR.
The PMDA must be using PMDA_PROTOCOL_6 or later, as specified in the call to pmdaDSO(3) or pmdaDaemon(3).
pmdaAttribute should return either zero on success, or a negative return code to indicate an error in handling the attribute. This return code cannot be used to indicate a client should be disallowed access - such functionality must be performed by the agent in response to callbacks for the client in question (using PM_ERR_PERMISSION for those specific callbacks, for that specific client. In other words, errors will be be passed to PMCD but there is no guarantee made that the error will be return to the client and result in termination of the client, for example.
PMAPI(3), PMDA(3), pmdaDaemon(3), pmdaDSO(3), pmdaMain(3) and pmdaGetContext(3).