about thread_info in task_struct

[Wenji Huang]

Hi,

 First thank jim! I got the write access for systemtap.

 There is some change about task_struct in sched.h (since 2.6.22)

>Commit f7e4217b007d1f73e7e3cf10ba4fea4a608c603f
>Author: Roman Zippel <zippel@linux-m68k.org>
>Date:   Wed May 9 02:35:17 2007 -0700
>
>    rename thread_info to stack
>    
>    This finally renames the thread_info field in task structure to stack, so that
>    the assumptions about this field are gone and archs have more freedom about
>    placing the thread_info structure.

Therefor task_test.stp failed.  Reason in tapset/task.stp:

>  function task_cpu:long (task:long)
>  %( kernel_v >= "2.6.23" %?
>  %{ /* pure */
   ........

So maybe need a little modification, kernel_v >= "2.6.22" or using macro task_thread_info
 
Another, I wrote function for returning task addr in case of only knowing pid:

/*return task addr according to process id*/
function get_task: long (pid:long) %{
        struct task_struct *p;
        pid_t pid;
        pid = (pid_t)(long)THIS->pid;
        rcu_read_lock();
        p = find_task_by_pid(pid);
        rcu_read_unlock();
        THIS->__retvalue = (long) p;
        CATCH_DEREF_FAULT();
%}

Please review it. 

Best regards,
Wenji