# _syscall

## 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:
    
               _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_.
    


## FILES



           _/usr/include/linux/unistd.h_
    


## STANDARDS



           Linux.
    


## NOTES



           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).
    


## EXAMPLES



           #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\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);
           }
    
       **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
    


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