RE: stucture element variable access problem

["Mao, Bibo" <bibo dot mao at intel dot com>]

My kernel version is 2.6.9-36.ELia32, and it will use $q->elevator.elevator_name get its name, for kernel >2.6.10  $q->elevator->elevator_type->elevator_name will be used to get the name.
My original meaning is that if variable is structure pointer type, it will be ok to access its element like "elevator_type->elevator_name". But if the variable is structure type but not pointer type, there will be error to access its element like "elevator.elevator_name".
In my IA32 and IA64 box, there will be the same error on 2.6.9-36.EL version. I do not know whether there is one method to access structure type variable's element.

Thanks
Bibo,mao

>-----Original Message-----
>From: Li Guanglei [mailto:guanglei@cn.ibm.com]
>Sent: 2006年5月19日 11:21
>To: Mao, Bibo
>Cc: systemtap@sources.redhat.com
>Subject: Re: stucture element variable access problem
>
>bibo,mao 写道:
>> Hi,
>> I encountered such problem when access structure element variable, if
>> the structure variable is pointer type, its element can be access, but
>> if the variable is structure type, there will be tapset translation
>> error when accessing its element. This is the test case:
>>
>> It will be ok with this test case:
>>     probe kernel.function("__elv_add_request")
>>     {
>>        if ($q->queue_tags){
>>                tag_map = $q->queue_tags->tag_map
>>                printf(" %d \n", tag_map);
>>        }
>>     }
>> But this test case will fail:
>>      probe kernel.function("__elv_add_request")
>>     {
>>        elevator_name = $q->elevator.elevator_name
>>     }
>> And there will be such error information:
>>
>I checked into SystemTap CVS the tapsets used by LKET. Now you can use:
>probe ioscheduler.elv_add_request
>{
>         printf("elv_name: %s\n", elevator_name)
>}
>
>I can't duplicate your errors on my box since my box used kernel 2.6.16.
>For kernel >= 2.6.10, you should use:
>$q->elevator->elevator_type->elevator_name to get the name.
>
>another comments is that you should use kernel_string to get the name.