Zabbix

/*

** Zabbix

** Copyright (C) 2001-2022 Zabbix SIA

**

** This program is free software; you can redistribute it and/or modify

** it under the terms of the GNU General Public License as published by

** the Free Software Foundation; either version 2 of the License, or

** (at your option) any later version.

**

** This program is distributed in the hope that it will be useful,

** but WITHOUT ANY WARRANTY; without even the implied warranty of

** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

** GNU General Public License for more details.

**

** You should have received a copy of the GNU General Public License

** along with this program; if not, write to the Free Software

** Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

**/

​

#include "procstat.h"

​

#include "log.h"

#include "stats.h"

#include "zbxnix.h"

​

​

#ifdef ZBX_PROCSTAT_COLLECTOR

​

/*

 * The process CPU statistics are stored using the following memory layout.

 *

 *  .--------------------------------------.

 *  | header                               |

 *  | ------------------------------------ |

 *  | process cpu utilization queries      |

 *  | and historical data                  |

 *  | ------------------------------------ |

 *  | free space                           |

 *  '--------------------------------------'

 *

 * Because the shared memory can be resized by other processes instead of

 * using pointers (when allocating strings, building single linked lists)

 * the memory offsets from the beginning of shared memory segment are used.

 * 0 offset is interpreted similarly to NULL pointer.

 *

 * Currently integer values are used to store offsets to internally allocated

 * memory which leads to 2GB total size limit.

 *

 * During every data collection cycle collector does the following:

 * 1) acquires list of all processes running on system

 * 2) builds a list of processes monitored by queries

 * 3) reads total cpu utilization snapshot for the monitored processes

 * 4) calculates cpu utilization difference by comparing with previous snapshot

 * 5) updates cpu utilization values for queries.

 * 6) saves the last cpu utilization snapshot

 *

 * Initialisation.

 * * zbx_procstat_init() initialises procstat dshm structure but doesn't allocate memory from the system

 *   (zbx_dshm_create() called with size 0).

 * * the first call of procstat_add() allocates the shared memory for the header and the first query

 *   via call to zbx_dshm_realloc().

 * * The header is initialised in procstat_copy_data() which is called back from zbx_dshm_realloc().

 *