_syscall — invoking a system call without library support (OBSOLETE)
#include <linux/unistd.h> A _syscall macro desired system call
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:
_syscall
X(type,name,type1,arg1,type2,arg2,...)
where
X is 0–6, which
are the number of arguments taken by the system
call
type is
the return type of the system call
name is
the name of the system call
typeN is
the Nth argument's type
argN is
the name of the Nth argument
These macros create a function called name with the arguments you
specify. Once you include the _syscall() in your source file,
you call the system call by name.
Starting around kernel 2.6.18, the _syscall macros were removed from header files supplied to user space. Use syscall(2) instead. (Some architectures, notably ia64, never provided the _syscall macros; on those architectures, syscall(2) was always required.)
The _syscall() macros do not produce a prototype. You may have to create one, especially for C++ users.
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, −EPERM. The _syscall() macros will return
the result r of the
system call when r
is non-negative, but will return −1 and set the
variable errno to
−r when
r is negative. For
the error codes, see errno(3).
When defining a system call, the argument types must be passed by-value or
by-pointer (for aggregates like structs).
#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);
/* Note: if you copy directly from the nroff source, remember to
REMOVE the extra backslashes in the printf statement. */
int
main(void)
{
struct sysinfo s_info;
int error;
error = sysinfo(&s_info);
printf("code error = %d\n", error);
printf("Uptime = %lds\nLoad: 1 min %lu / 5 min %lu / 15 min %lu\n"
"RAM: total %lu / free %lu / shared %lu\n"
"Memory in buffers = %lu\nSwap: total %lu / free %lu\n"
"Number of processes = %d\n",
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);
}
This page is part of release 2.79 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
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Copyright (c) 1993 Michael Haardt (michaelmoria.de), Fri Apr 2 11:32:09 MET DST 1993 This is free documentation; 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. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual 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 manual; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. Tue Jul 6 12:42:46 MDT 1993 <dminernyx.cs.du.edu> Added "Calling Directly" and supporting paragraphs Modified Sat Jul 24 15:19:12 1993 by Rik Faith <faithcs.unc.edu> Modified 21 Aug 1994 by Michael Chastain <mecshell.portal.com>: Added explanation of arg stacking when 6 or more args. Modified 10 June 1995 by Andries Brouwer <aebcwi.nl> 2007-10-23 mtk: created as a new page, by taking the content specific to the _syscall() macros from intro(2). |