RE: stucture element variable access problem

RE: stucture element variable access problem

[Mao, Bibo]

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.

Re: stucture element variable access problem

[Li Guanglei]

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Mao, Bibo дµÀ:
> 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.
> 
You should use:
$q->elevator->elevator_name
instead of:
$q->elevator.elevator_name

The following script works well for me on 2.6.9-34.19.EL/ppc64

probe kernel.function("__elv_add_request")
{
        elevator_name = kernel_string($q->elevator->elevator_name)
        printf("%s\n", elevator_name)
}

RE: stucture element variable access problem

[Mao, Bibo]

Oh, yes it is. That works for me now :)

Thanks
Bibo,mao

>-----Original Message-----
>From: Li Guanglei [mailto:guanglei@cn.ibm.com]
>Sent: 2006年5月19日 12:24
>To: Mao, Bibo
>Cc: systemtap@sources.redhat.com
>Subject: Re: stucture element variable access problem
>
>Mao, Bibo 写道:
>> 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.
>>
>You should use:
>$q->elevator->elevator_name
>instead of:
>$q->elevator.elevator_name
>
>The following script works well for me on 2.6.9-34.19.EL/ppc64
>
>probe kernel.function("__elv_add_request")
>{
>        elevator_name = kernel_string($q->elevator->elevator_name)
>        printf("%s\n", elevator_name)
>}

Re: stucture element variable access problem

[Li Guanglei]

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.

stucture element variable access problem

[bibo,mao]

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:

probe __elv_add_request@drivers/block/elevator.c:171 pc=0xc02017e2
pattern 'kernel' matches module 'kernel'
keeping expression operator '=' at 1.stp:3:16 because it writes: elevator_name and/or embedded: 0
semantic error: unresolved target-symbol expression: identifier '$q' at 1.stp:3:18
semantic error: probe_0 with unresolved type for identifier 'elevator_name' at 1.stp:3:2
semantic error: unresolved target-symbol expression: identifier '$q' at 1.stp:3:18
Pass 2: analyzed script: 1 probe(s), 0 function(s), 0 global(s) in 210usr/30sys/224real ms.
Pass 2: analysis failed.  Try again with more '-v' (verbose) options.

thanks
bibo,mao