.\" .\" Copyright (c) 2020-2023 Jim Warner .\" Copyright (c) 2020-2023 Craig Small .\" .\" This manual is free software; you can redistribute it and/or .\" modify it under the terms of the GNU Lesser General Public .\" License as published by the Free Software Foundation; either .\" version 2.1 of the License, or (at your option) any later version. .\" .\" .TH PROCPS 3 "August 2022" "libproc2" .\" Please adjust this date whenever revising the manpage. .\" .nh .SH NAME procps \- API to access system level information in the /proc filesystem .SH SYNOPSIS Five distinct interfaces are represented in this synopsis and named after the files they access in the /proc pseudo filesystem: .BR diskstats ", " meminfo ", " slabinfo ", " stat " and " vmstat . .nf .RS +4 #include .RI "int\fB procps_new \fR (struct info **" info ); .RI "int\fB procps_ref \fR (struct info *" info ); .RI "int\fB procps_unref\fR (struct info **" info ); .RB "struct result *" procps_get " (" .RI " struct info *" info , .RI "[ const char *" name ", ] \fBdiskstats\fR api only" .RI " enum item " item ); .RB "struct stack *" procps_select " (" .RI " struct info *" info , .RI "[ const char *" name ", ] \fBdiskstats\fR api only" .RI " enum item *" items , .RI " int " numitems ); .RB "struct reaped *" procps_reap " (" .RI " struct info *" info , .RI "[ enum reap_type " what ", ] \fBstat\fR api only" .RI " enum item *" items , .RI " int " numitems ); .RB "struct stack **" procps_sort " (" .RI " struct info *" info , .RI " struct stack *" stacks [], .RI " int " numstacked , .RI " enum item " sortitem , .RI " enum sort_order " order ); .fi The above functions and structures are generic but the specific \fBnamed_interface\fR would also be part of any identifiers. For example, `procps_new' would actually be `procps_\fBmeminfo\fR_new' and `info' would really be `\fBdiskstats\fR_info', etc. The same \fBnamed_interface\fR is used in each header file name with an appended `.h' suffix. Link with \fI\-lproc2\fP. .SH DESCRIPTION .SS Overview Central to these interfaces is a simple `result' structure reflecting an `item' plus its value (in a union with standard C language types as members). All `result' structures are automatically allocated and provided by the library. By specifying an array of `items', these structures can be organized as a `stack', potentially yielding many results with a single function call. Thus, a `stack' can be viewed as a variable length record whose content and order is determined solely by the user. As part of each interface there are two unique enumerators. The `noop' and `extra' items exist to hold user values. They are never set by the library, but the `extra' result will be zeroed with each library interaction. The \fBnamed_interface\fR header file will be an essential document during user program development. There you will find available items, their return type (the `result' struct member name) and the source for such values. Additional enumerators and structures are also documented there. .SS Usage The following would be a typical sequence of calls to these interfaces. .nf .RB "1. " procps_new() .RB "2. " procps_get() ", " procps_select() " or " procps_reap() .RB "3. " procps_unref() .fi The \fBget\fR function is used to retrieve a `result' structure for a single `item'. Alternatively, a \fBGET\fR macro is available when only the return value is of interest. The \fBselect\fR function can retrieve multiple `result' structures in a single `stack'. For unpredictable variable outcomes, the \fBdiskstats\fR, \fBslabinfo\fR and \fBstat\fR interfaces export a \fBreap\fR function. It is used to retrieve multiple `stacks' each containing multiple `result' structures. Optionally, a user may choose to \fBsort\fR those results. To exploit any `stack', and access individual `result' structures, a \fIrelative_enum\fR is required as shown in the \fBVAL\fR macro defined in the header file. Such values could be hard coded as: 0 through numitems-1. However, this need is typically satisfied by creating your own enumerators corresponding to the order of the `items' array. .SS Caveats The \fBnew\fR, \fBref\fR, \fBunref\fR, \fBget\fR and \fBselect\fR functions are available in all five interfaces. For the \fBnew\fR and \fBunref\fR functions, the address of an \fIinfo\fR struct pointer must be supplied. With \fBnew\fR it must have been initialized to NULL. With \fBunref\fR it will be reset to NULL if the reference count reaches zero. In the case of the \fBdiskstats\fR interface, a \fIname\fR parameter on the \fBget\fR and \fBselect\fR functions identifies a disk or partition name For the \fBstat\fR interface, a \fIwhat\fR parameter on the \fBreap\fR function identifies whether data for just CPUs or both CPUs and NUMA nodes is to be gathered. When using the \fBsort\fR function, the parameters \fIstacks\fR and \fInumstacked\fR would normally be those returned in the `reaped' structure. .SH RETURN VALUE .SS Functions Returning an `int' An error will be indicated by a negative number that is always the inverse of some well known errno.h value. Success is indicated by a zero return value. However, the \fBref\fR and \fBunref\fR functions return the current \fIinfo\fR structure reference count. .SS Functions Returning an `address' An error will be indicated by a NULL return pointer with the reason found in the formal errno value. Success is indicated by a pointer to the named structure. .SH DEBUGGING To aid in program development, there is a provision that can help ensure `result' member references agree with library expectations. It assumes that a supplied macro in the header file is used to access the `result' value. This feature can be activated through either of the following methods and any discrepancies will be written to \fBstderr\fR. .IP 1) 3 Add CFLAGS='-DXTRA_PROCPS_DEBUG' to any other ./configure options employed. .IP 2) 3 Add #include to any program \fIafter\fR the named interface includes. .PP This verification feature incurs substantial overhead. Therefore, it is important that it \fInot\fR be activated for a production/release build. .SH SEE ALSO .BR procps_misc (3), .BR procps_pids (3), .BR proc (5).