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

       _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:



              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.


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

       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 architec-
       tures, 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

       #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. */

           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,

   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

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

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2007-12-19                       _SYSCALL(2)