asmlinkage long sys_getpid(void)
{

return current->tgid;

}

 ,         .
      ,  -
    , ,    -
. ,       -
  ,   ,        
   (       )5.

       ,  -
  . -,     
asmlinkage   .      -
  ,        
  .       
 . -,   ,   -
 getpid ()   ,  sys_getpid ().    
        Linux: -
  bar ()       sys_bar ().

  

     Linux  
  (syscall number).      
   .      
 ,        .

     .  
    ,      -
  .    ,  
    .    Linux -
   " " ("not implemented")   
 sys ni syscall (),    ,  ,  
,  -ENOSYS,  ,   -
 .     " "     -
,    .

       
 .     ,    -
 sys_call_table.        
   entry. S.      
      syscall.

5  , ,   getpid ()   tgid,   -
   (thread group ID)?   ,    
  TGID    PID.     -
  TGID      .    -
     getpid ()     -
 PID.

98  5