2 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
3 .\" Fri Apr 2 11:32:09 MET DST 1993
5 .\" This is free documentation; you can redistribute it and/or
6 .\" modify it under the terms of the GNU General Public License as
7 .\" published by the Free Software Foundation; either version 2 of
8 .\" the License, or (at your option) any later version.
10 .\" The GNU General Public License's references to "object code"
11 .\" and "executables" are to be interpreted as the output of any
12 .\" document formatting or typesetting system, including
13 .\" intermediate and printed output.
15 .\" This manual is distributed in the hope that it will be useful,
16 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
17 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 .\" GNU General Public License for more details.
20 .\" You should have received a copy of the GNU General Public
21 .\" License along with this manual; if not, write to the Free
22 .\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
25 .\" Tue Jul 6 12:42:46 MDT 1993 <dminer@nyx.cs.du.edu>
26 .\" Added "Calling Directly" and supporting paragraphs
28 .\" Modified Sat Jul 24 15:19:12 1993 by Rik Faith <faith@cs.unc.edu>
30 .\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>:
31 .\" Added explanation of arg stacking when 6 or more args.
33 .\" Modified 10 June 1995 by Andries Brouwer <aeb@cwi.nl>
35 .\" 2007-10-23 mtk: created as a new page, by taking the content
36 .\" specific to the _syscall() macros from intro(2).
38 .TH _SYSCALL 2 2007-12-19 "Linux" "Linux Programmer's Manual"
40 _syscall \- invoking a system call without library support (OBSOLETE)
42 .B #include <linux/unistd.h>
48 The important thing to know about a system call is its prototype.
49 You need to know how many arguments, their types,
50 and the function return type.
51 There are seven macros that make the actual call into the system easier.
55 .RI _syscall X ( type , name , type1 , arg1 , type2 , arg2 ,...)
60 \fIX\fP is 0\(en6, which are the number of arguments taken by the
63 \fItype\fP is the return type of the system call
65 \fIname\fP is the name of the system call
67 \fItypeN\fP is the Nth argument's type
69 \fIargN\fP is the name of the Nth argument
71 These macros create a function called \fIname\fP with the arguments you
73 Once you include the _syscall() in your source file,
74 you call the system call by \fIname\fP.
76 .I /usr/include/linux/unistd.h
78 The use of these macros is Linux-specific, and deprecated.
80 Starting around kernel 2.6.18, the _syscall macros were removed
81 from header files supplied to user space.
85 (Some architectures, notably ia64, never provided the _syscall macros;
86 on those architectures,
90 The _syscall() macros \fIdo not\fP produce a prototype.
92 create one, especially for C++ users.
94 System calls are not required to return only positive or negative error
96 You need to read the source to be sure how it will return errors.
97 Usually, it is the negative of a standard error code,
98 for example, \-\fBEPERM\fP.
99 The _syscall() macros will return the result \fIr\fP of the system call
100 when \fIr\fP is nonnegative, but will return \-1 and set the variable
102 to \-\fIr\fP when \fIr\fP is negative.
103 For the error codes, see
106 When defining a system call, the argument types \fImust\fP be
107 passed by-value or by-pointer (for aggregates like structs).
108 .\" The preferred way to invoke system calls that glibc does not know
111 .\" However, this mechanism can only be used if using a libc
112 .\" (such as glibc) that supports
115 .\" .I <sys/syscall.h>
116 .\" header file contains the required SYS_foo definition.
117 .\" Otherwise, the use of a _syscall macro is required.
124 #include <linux/unistd.h> /* for _syscallX macros/related stuff */
125 #include <linux/kernel.h> /* for struct sysinfo */
127 _syscall1(int, sysinfo, struct sysinfo *, info);
129 /* Note: if you copy directly from the nroff source, remember to
130 REMOVE the extra backslashes in the printf statement. */
135 struct sysinfo s_info;
138 error = sysinfo(&s_info);
139 printf("code error = %d\\n", error);
140 printf("Uptime = %lds\\nLoad: 1 min %lu / 5 min %lu / 15 min %lu\\n"
141 "RAM: total %lu / free %lu / shared %lu\\n"
142 "Memory in buffers = %lu\\nSwap: total %lu / free %lu\\n"
143 "Number of processes = %d\\n",
144 s_info.uptime, s_info.loads[0],
145 s_info.loads[1], s_info.loads[2],
146 s_info.totalram, s_info.freeram,
147 s_info.sharedram, s_info.bufferram,
148 s_info.totalswap, s_info.freeswap,
157 Load: 1 min 13376 / 5 min 5504 / 15 min 1152
158 RAM: total 15343616 / free 827392 / shared 8237056
159 Memory in buffers = 5066752
160 Swap: total 27881472 / free 24698880
161 Number of processes = 40