__pmFreeHostAttrsSpec(3) — Linux manual page



NAME         top

       __pmParseHostAttrsSpec,   __pmUnparseHostAttrsSpec,   __pmFreeHostAt‐
       trsSpec, __pmFreeAttrsSpec - host and attributes specification parser

C SYNOPSIS         top

       #include "pmapi.h"
       #include "libpcp.h"

       int __pmParseHostAttrsSpec(const char *string, pmHostSpec **hostsp,
               int *count, __pmHashCtl *attrs, char **errmsg);
       int __pmUnparseHostAttrsSpec(pmHostSpec *hostsp, int *count,
               __pmHashCtl *attrs, char *string, size_t size);
       void __pmFreeHostAttrsSpec(pmHostSpec *hosts, int count,
               __pmHashCtl *attrs);
       void __pmFreeAttrsSpec(__pmHashCtl *attrs);

       cc ... -lpcp

CAVEAT         top

       This documentation is intended for internal Performance Co-Pilot
       (PCP) developer use.

       These interfaces are not part of the PCP APIs that are guaranteed to
       remain fixed across releases, and they may not work, or may provide
       different semantics at some point in the future.

DESCRIPTION         top

       __pmParseHostAttrsSpec accepts a string specifying the location of a
       PCP performance metric collector daemon, and any attributes that
       should be associated with the connection to that daemon.

       The syntax allows the optional specification of a protocol (native
       PCP protocol, encrypted PCP protocol or unix domain socket protocol).

       If the specified protocol is native PCP protocol, or encrypted PCP
       protocol, an initial pmcd(1) hostname with optional port numbers and
       optional proxy host, and optional attributes which are to be
       associated with the connection may be specified.  Some examples


       If the specified protocol is a unix domain socket protocol, the path
       to the socket in the local file system may be specified along with
       optional attributes which are to be associated with the connection.
       For example:


       If the optional protocol component is not specified, then the default
       setting will be used - which is the native PCP binary protocol.
       However, this can still be overwritten via the environment as
       described in PCPIntro(1).  If the protocol prefix is specified, it
       must be one of either "pcp://" (clear), "pcps://" (secure,
       encrypted), "unix://" (authenticated local) or "local://" ("unix://"
       then "pcp://").

       The path specified for the "unix://" and "local://" protocols will
       always be interpreted as an absolute path name. For example, the
       following are all interpreted identically as


       Refer to __pmParseHostSpec(3) for further details of the host and
       proxy host components.

       If any optional connection attributes are to be specified, these are
       separated from the hostname component via the '?' character.  Each
       attribute is separated by the '&' character, and each can be either a
       simple attribute flag (such as "compress") or a name=value pair (such
       as "username=fred").

       __pmParseHostAttrsSpec takes a null-terminated host-and-attributes
       specification string and returns an array of pmHostSpec structures,
       where the array has count entries, and an attrs hash table containing
       any attributes (including the optional protocol, if it was

       Full details of the pmHostSpec structures are provided in

       The __pmHashCtl structure that is filled out on return via
       attributes, represents each individual attribute in the specification
       string with any associated value.  It should be considered an opaque
       structure and should be zeroed beforehand.

       The returned hash table control structure can be iterated using one
       of the supplied iteration mechanisms - __pmHashWalkCB (a callback-
       based mechanism) or __pmHashWalk (a simple procedural mechanism).
       These provide access to the individual hash nodes, as __pmHashNode
       entries, which provide access to decoded attributes and their
       (optional) values.

           typedef struct __pmHashNode {
               __pmHashNode    *next;    /* next node in hash bucket (internal) */
               unsigned int    key;      /* key identifying particular attribute */
               void            *data;    /* attributes value (optional, string) */
           } __pmHashNode;

       There are a set number of valid attributes, however these may be
       extended in future releases as new connection parameters become
       needed.  These can be identified via the PCP_ATTR_* macros in the PCP
       header files.

       __pmUnparseHostSpec performs the inverse operation, creating a string
       representation from hosts and attributes structures.  The size of the
       supplied string buffer must be provided by the caller using the size

RETURN VALUE         top

       If the given string is successfully parsed __pmParseHostAttrsSpec
       returns zero.  In this case the dynamic storage allocated by
       __pmParseHostAttrsSpec can be released by calling
       __pmFreeHostAttrsSpec using the addresses returned from

       Alternatively, the hosts and attributes memory can be freed
       separately, using __pmFreeHostSpec(3) and __pmFreeAttrsSpec.

       __pmParseHostAttrsSpec returns PM_ERR_GENERIC and a dynamically
       allocated error message string in errmsg, if the given string does
       not parse, and the user-supplied errmsg pointer is non-null.  Be sure
       to free(3) the error message string in this situation.

       In the case of an error, both hosts and attributes are undefined.  In
       the case of success, errmsg is undefined.

       On success __pmUnparseHostAttrsSpec returns a positive value
       indicating the number of characters written into the supplied buffer.
       However, if the supplied buffer was too small, a negative status code
       of -E2BIG will be returned.

SEE ALSO         top

       pmcd(1), pmproxy(1), pmchart(1), __pmParseHostSpec(3), PMAPI(3) and

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at ⟨http://www.pcp.io/⟩.
       If you have a bug report for this manual page, send it to
       pcp@groups.io.  This page was obtained from the project's upstream
       Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
       2020-08-13.  (At that time, the date of the most recent commit that
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       (which is not part of the original manual page), send a mail to

Performance Co-Pilot                 PCP             PMPARSEHOSTATTRSSPEC(3)