pmdaAttribute(3) — Linux manual page


PMDAATTRIBUTE(3)          Library Functions Manual          PMDAATTRIBUTE(3)

NAME         top

       pmdaAttribute - informs a PMDA about client connection attributes

C SYNOPSIS         top

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

       int pmdaAttribute(int context, int key, char *value, int length,
       pmdaExt *pmda);

       cc ... -lpcp_pmda -lpcp

DESCRIPTION         top

       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.

DIAGNOSTICS         top

       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.

CAVEAT         top

       The PMDA must be using PMDA_PROTOCOL_6 or later, as specified in the
       call to pmdaDSO(3) or pmdaDaemon(3).

SEE ALSO         top

       PMAPI(3), PMDA(3), pmdaDaemon(3), pmdaDSO(3), pmdaMain(3) and

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at ⟨⟩.
       If you have a bug report for this manual page, send it to  This page was obtained from the project's upstream
       Git repository ⟨⟩ on
       2020-09-18.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-09-18.)  If you discover any
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       (which is not part of the original manual page), send a mail to

Performance Co-Pilot                 PCP                    PMDAATTRIBUTE(3)

Pages that refer to this page: pmdaGetContext(3)pmdamain(3)pmdaMain(3)pmdaSetCheckCallBack(3)pmdaSetDoneCallBack(3)pmdaSetEndContextCallBack(3)pmdaSetResultCallBack(3)