pmdaAttribute - informs a PMDA about client connection attributes
#include <pcp/pmapi.h>
#include <pcp/pmda.h>
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).