Re: Few queries on tapset interface

[Jim Keniston <jkenisto at us dot ibm dot com>]

On Wed, 2005-06-01 at 13:22, Frank Ch. Eigler wrote:
...
> This would be closer to current syntax:
> 
> global entry_time, my_count, my_fd, read_times
> 
> probe kernel.syscall("read") {
>       thread->entry_time = $timestamp; # "macro" variable

Sample code - yay!  I have some suggestions...

If we're going to use $var to mean "var in the context of the probed
function," then I think it's confusing to start names of
language-defined values (such as $timestamp) with '$' as well.  We also
run the risk of name collisions.  Perhaps use @ (or $_) for the former
and $ for the latter.

I think that the thread->assoc_array syntax is confusing, especially now
that the language supports the C-language meaning of ->.  I think
entry_time[$thread] would be clearer than thread->entry_time (assuming
$thread gets you a thread- or task-specific number).

>       thread->my_count = $count; # function argument
>       thread->my_fd = $fd; # function argument
>       trace ("my_count = " . string(thread->my_count) .
>              "my_fd = " . string(thread->my_fd))
> }
> 
> probe kernel.syscall("read").return {
>       if (thread->entry_time) {
>          read_times[$syscall_name]    # variable from provider alias

If it's from the provider alias, wouldn't it be just syscall_name, not
$syscall_name?

>             += $timestamp - thread->entry_time
>       }
>       trace ("syscall " . $syscall_name .
>              " return value = " .
>              hexstring ($retvalue));  # function pseudo-argument
> }

The runtime provides _stp_printf() for printk-like logging, so you could
do something like
	_stp_printf("syscall %s return value = %#x\n",
		$syscall_name, $retvalue);
although you might not call _stp_printf by its real name, in case we
need to preserve the abstraction.

> 
> probe end {
>       for ([syscall] in read_times) {

Why "[syscall]" rather than "syscall" in the "for" clause?

>           trace ("syscall " . syscall .
>                  " total-time=" . string (read_times[syscall]))
>       }
> }
> 
...
> 
> - FChE
> 

Jim