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    Command:

    _syscall

    
    
    

    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 spec-
           ify.  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 cre-
           ate 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 vari-
    
           /* 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);
           }
    
       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)
    
    
    

    Linux 2007-12-19 _SYSCALL(2)

    
    
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