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Diffstat (limited to 'man2/_syscall.2')
| -rw-r--r-- | man2/_syscall.2 | 171 |
1 files changed, 171 insertions, 0 deletions
diff --git a/man2/_syscall.2 b/man2/_syscall.2 new file mode 100644 index 0000000..ef6542f --- /dev/null +++ b/man2/_syscall.2 @@ -0,0 +1,171 @@ +.\" Copyright (c) 1993 Michael Haardt (michael@moria.de), +.\" Fri Apr 2 11:32:09 MET DST 1993 +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.\" Tue Jul 6 12:42:46 MDT 1993 <dminer@nyx.cs.du.edu> +.\" Added "Calling Directly" and supporting paragraphs +.\" +.\" Modified Sat Jul 24 15:19:12 1993 by Rik Faith <faith@cs.unc.edu> +.\" +.\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>: +.\" Added explanation of arg stacking when 6 or more args. +.\" +.\" Modified 10 June 1995 by Andries Brouwer <aeb@cwi.nl> +.\" +.\" 2007-10-23 mtk: created as a new page, by taking the content +.\" specific to the _syscall() macros from intro(2). +.\" +.TH _syscall 2 2023-05-03 "Linux man-pages 6.05.01" +.SH NAME +_syscall \- invoking a system call without library support (OBSOLETE) +.SH SYNOPSIS +.nf +.B #include <linux/unistd.h> +.PP +A _syscall macro +.PP +desired system call +.fi +.SH DESCRIPTION +The important thing to know about a system call is its prototype. +You need to know how many arguments, their types, +and the function return type. +There are seven macros that make the actual call into the system easier. +They have the form: +.PP +.in +4n +.EX +.RI _syscall X ( type , name , type1 , arg1 , type2 , arg2 ,...) +.EE +.in +.PP +where +.IP +.I X +is 0\[en]6, which are the number of arguments taken by the +system call +.IP +.I type +is the return type of the system call +.IP +.I name +is the name of the system call +.IP +.I typeN +is the Nth argument's type +.IP +.I argN +is the name of the Nth argument +.PP +These macros create a function called +.I name +with the arguments you +specify. +Once you include the _syscall() in your source file, +you call the system call by +.IR name . +.SH FILES +.I /usr/include/linux/unistd.h +.SH STANDARDS +Linux. +.SH HISTORY +Starting around Linux 2.6.18, the _syscall macros were removed +from header files supplied to user space. +Use +.BR syscall (2) +instead. +(Some architectures, notably ia64, never provided the _syscall macros; +on those architectures, +.BR syscall (2) +was always required.) +.SH NOTES +The _syscall() macros +.I "do not" +produce a prototype. +You may have to +create one, especially for C++ users. +.PP +System calls are not required to return only positive or negative error +codes. +You need to read the source to be sure how it will return errors. +Usually, it is the negative of a standard error code, +for example, +.RI \- EPERM . +The _syscall() macros will return the result +.I r +of the system call +when +.I r +is nonnegative, but will return \-1 and set the variable +.I errno +to +.RI \- r +when +.I r +is negative. +For the error codes, see +.BR errno (3). +.PP +When defining a system call, the argument types +.I must +be +passed by-value or by-pointer (for aggregates like structs). +.\" The preferred way to invoke system calls that glibc does not know +.\" about yet is via +.\" .BR syscall (2). +.\" However, this mechanism can be used only if using a libc +.\" (such as glibc) that supports +.\" .BR syscall (2), +.\" and if the +.\" .I <sys/syscall.h> +.\" header file contains the required SYS_foo definition. +.\" Otherwise, the use of a _syscall macro is required. +.\" +.SH EXAMPLES +.\" [[deprecated]] SRC BEGIN (_syscall.c) +.EX +#include <stdio.h> +#include <stdlib.h> +#include <errno.h> +#include <linux/unistd.h> /* for _syscallX macros/related stuff */ +#include <linux/kernel.h> /* for struct sysinfo */ +\& +_syscall1(int, sysinfo, struct sysinfo *, info); +\& +int +main(void) +{ + struct sysinfo s_info; + int error; +\& + error = sysinfo(&s_info); + printf("code error = %d\en", error); + printf("Uptime = %lds\enLoad: 1 min %lu / 5 min %lu / 15 min %lu\en" + "RAM: total %lu / free %lu / shared %lu\en" + "Memory in buffers = %lu\enSwap: total %lu / free %lu\en" + "Number of processes = %d\en", + s_info.uptime, s_info.loads[0], + s_info.loads[1], s_info.loads[2], + s_info.totalram, s_info.freeram, + s_info.sharedram, s_info.bufferram, + s_info.totalswap, s_info.freeswap, + s_info.procs); + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SS Sample output +.EX +code error = 0 +uptime = 502034s +Load: 1 min 13376 / 5 min 5504 / 15 min 1152 +RAM: total 15343616 / free 827392 / shared 8237056 +Memory in buffers = 5066752 +Swap: total 27881472 / free 24698880 +Number of processes = 40 +.EE +.SH SEE ALSO +.BR intro (2), +.BR syscall (2), +.BR errno (3) |