dtrace discuss - Dec 2008 - Dtrace dummy and Conditional Expressions

Happy Friday,

I''m having a hard time wrapping my head around the proper way to use
conditional expressions in DTrace.

The following line seems to not want to compile:

args[0]->b_flags & B_READ ? (
@dev_r[args[1]->dev_statname,args[1]->dev_pathname]=sum(args[0]->b_bcount)
) : ( @dev_w[args[1]->dev_statname]=sum(args[0]->b_bcount) );

I get the following error:

  dtrace: failed to compile script ./script.d: line 6: operator ?:
operands cannot be of dynamic type

My general (and apparently wrong) understanding is that all three
expressions should evaluate to either true or false so (B_READ bit is
set or not, @dev_r aggregate gets populated or not, or the @dev_w
aggregate gets populated or not).  It seems on the surface to be
pretty strait forward....but of course I am missing something.

Any help would be appreciated.
--Brett

On Fri, Dec 12, 2008 at 12:05:21PM -0800, Brett Monroe
wrote:
> Happy Friday,
> 
> I''m having a hard time wrapping my head around the proper way to
use
> conditional expressions in DTrace.
> 
> The following line seems to not want to compile:
> 
> args[0]->b_flags & B_READ ? (
>
@dev_r[args[1]->dev_statname,args[1]->dev_pathname]=sum(args[0]->b_bcount)
> ) : ( @dev_w[args[1]->dev_statname]=sum(args[0]->b_bcount) );
You cannot use conditional expressions to do different actions; they can
only be used in expressions.  You need to use predicates:

io:::start
/ args[0]->b_flags & B_READ /
{
	@dev_r[args[1]->dev_statname,args[1]->dev_pathname] 	   
sum(args[0]->b_bcount);
}

io:::start
/ !(args[0]->b_flags & B_READ) /
{
	@dev_w[args[1]->dev_statname] = sum(args[0]->b_bcount);
}

Cheers,
- jonathan
> I get the following error:
> 
>   dtrace: failed to compile script ./script.d: line 6: operator ?:
> operands cannot be of dynamic type
> 
> My general (and apparently wrong) understanding is that all three
> expressions should evaluate to either true or false so (B_READ bit is
> set or not, @dev_r aggregate gets populated or not, or the @dev_w
> aggregate gets populated or not).  It seems on the surface to be
> pretty strait forward....but of course I am missing something.
> 
> Any help would be appreciated.
> --Brett
> _______________________________________________
> dtrace-discuss mailing list
> dtrace-discuss at opensolaris.org

Ahh, wonderful.  Thanks Jonathan!

--Brett

On Fri, Dec 12, 2008 at 12:51 PM, Jonathan Adams <jonathan.adams at
sun.com> wrote:
> On Fri, Dec 12, 2008 at 12:05:21PM -0800, Brett Monroe wrote:
>> Happy Friday,
>>
>> I''m having a hard time wrapping my head around the proper way
to use
>> conditional expressions in DTrace.
>>
>> The following line seems to not want to compile:
>>
>> args[0]->b_flags & B_READ ? (
>>
@dev_r[args[1]->dev_statname,args[1]->dev_pathname]=sum(args[0]->b_bcount)
>> ) : ( @dev_w[args[1]->dev_statname]=sum(args[0]->b_bcount) );
>
> You cannot use conditional expressions to do different actions; they can
> only be used in expressions.  You need to use predicates:
>
> io:::start
> / args[0]->b_flags & B_READ /
> {
>        @dev_r[args[1]->dev_statname,args[1]->dev_pathname] >      
sum(args[0]->b_bcount);
> }
>
> io:::start
> / !(args[0]->b_flags & B_READ) /
> {
>        @dev_w[args[1]->dev_statname] = sum(args[0]->b_bcount);
> }
>
> Cheers,
> - jonathan
>
>> I get the following error:
>>
>>   dtrace: failed to compile script ./script.d: line 6: operator ?:
>> operands cannot be of dynamic type
>>
>> My general (and apparently wrong) understanding is that all three
>> expressions should evaluate to either true or false so (B_READ bit is
>> set or not, @dev_r aggregate gets populated or not, or the @dev_w
>> aggregate gets populated or not).  It seems on the surface to be
>> pretty strait forward....but of course I am missing something.
>>
>> Any help would be appreciated.
>> --Brett
>> _______________________________________________
>> dtrace-discuss mailing list
>> dtrace-discuss at opensolaris.org
>