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__pmlookupipc(3) — Linux manual page

NAME | C SYNOPSIS | CAVEAT | DESCRIPTION | DIAGNOSTICS | SEE ALSO | COLOPHON 

PMLOOKUPIPC(3)           Library Functions Manual          PMLOOKUPIPC(3)

NAME         top

       __pmOverrideLastFd, __pmPrintIPC, __pmResetIPC - IPC version
       infrastructure support

C SYNOPSIS         top

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

       void __pmOverrideLastFd(int fd);
       void __pmPrintIPC(void);
       void __pmResetIPC(int fd);

       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

       IPC channels throughout the distributed PCP framework are affected
       by the PCP 2.0 (and later) PDU changes.  These functions  are  the
       interface  to  the  libpcp  IPC connection management global data.
       This data consists of a hash table of __pmIPC structures  (indexed
       by file descriptor) and a cached, most-recently-used file descrip‐
       tor.

       The  __pmOverrideLastFd  is  an  escape mechanism for use in those
       situations where the last PDU fetch did not go through  the  usual
       channels  (i.e.  __pmGetPDU), so as to ensure that the cached file
       descriptor is the correct file descriptor for  the  PDU  which  is
       currently  being  processed.   This  will  typically  be  used for
       archive PDU processing or where version information is not  avail‐
       able  for a given file descriptor (e.g. immediately prior to a PDU
       version exchange).

       __pmPrintIPC is a useful debugging routine for displaying a  table
       mapping all currently registered file descriptors to their associ‐
       ated  PDU  version  numbers.   Unused entries in this table should
       display the value zero in the version column.

       __pmResetIPC resets the version information  associated  with  the
       given  file descriptor to some known (invalid) number.  Subsequent
       lookups on this file descriptor will return an UNKNOWN_VERSION em‐
       bedded within the __pmIPC structure.

DIAGNOSTICS         top

       A negative return value from __pmOverrideLastFd indicates that the
       file descriptor argument is not  registered  in  the  hash  table.
       This  typically indicates closure of an IPC channel, so PM_ERR_IPC
       is returned if this is the case.

SEE ALSO         top

       PMAPI(3)

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.   In‐
       formation  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
       2025-08-11.  (At that time, the date of  the  most  recent  commit
       that was found in the repository was 2025-08-11.)  If you discover
       any  rendering  problems  in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the  page,
       or you have corrections or improvements to the information in this
       COLOPHON  (which  is not part of the original manual page), send a
       mail to man-pages@man7.org

Performance Co-Pilot               PCP                     PMLOOKUPIPC(3)

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