_SYSCALL(2)						     Linux Programmer's Manual						       _SYSCALL(2)

NAME

       _syscall - invoking a system call without library support (OBSOLETE)

SYNOPSIS

       #include <linux/unistd.h>

       A _syscall macro

       desired system call

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:

	      _syscallX(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.

FILES

       /usr/include/linux/unistd.h

CONFORMING TO

       The use of these macros is Linux-specific, and deprecated.

NOTES

       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 nonnegative, 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).

EXAMPLE

       #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
", error);
	   printf("Uptime = %lds
Load: 1 min %lu / 5 min %lu / 15 min %lu
"
		  "RAM: total %lu / free %lu / shared %lu
"
		  "Memory in buffers = %lu
Swap: total %lu / free %lu
"
		  "Number of processes = %d
",
		  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);
       }

   Sample Output
       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

SEE ALSO

       intro(2), syscall(2), errno(3)

COLOPHON

       This  page is part of release 3.25 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/.

Linux								    2007-12-19							       _SYSCALL(2)