pmparsehostattrsspec(3) — Linux manual page



NAME         top

       __pmParseHostAttrsSpec, __pmUnparseHostAttrsSpec,
       __pmFreeHostAttrsSpec, __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 follow:


       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 specified).

       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 parameter.

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 pmNewContext(3).

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 2023-12-22.
       (At that time, the date of the most recent commit that was found
       in the repository was 2023-12-16.)  If you discover any rendering
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       (which is not part of the original manual page), send a mail to

Performance Co-Pilot               PCP           PMPARSEHOSTATTRSSPEC(3)

Pages that refer to this page: pmparsehostspec(3)