[DTrace-devel] [PATCH 1/5] Change use of dtrace_probe_iter()

[Eugene Loh]

On 06/12/2020 04:55 PM, Kris Van Hees wrote:

> On Thu, Jun 11, 2020 at 05:29:37PM -0400, eugene.loh at oracle.com wrote:
>> From: Eugene Loh <eugene.loh at oracle.com>
>>
>> In DTrace v1, dtrace_probe_iter() was used to iterate over probes,
>> using dt_probe_iter() as a callback function.
>>
>> In the current release, dtrace_probe_iter() will be used as an external
>> API, with dt_probe_iter() the "internal" (to libdtrace) interface.
> I am not against this patch but I also do not see the need for it.

Need?  I suppose there is no need.  It was simply my interpretation of 
your earlier comments.  I suppose, however, that there is also no need 
to call the dtrace_* wrapper if one can call the internal dt_* function 
directly.

> It is not
> wrong for libdtrace code to use dtrace_probe_iter.  My intent was that the code
> that uses dtrace_probe_iter would continue to use it, and only have direct
> calls to dt_probe_iter done for cases where we need the callback function to
> have access to the actual dt_probe_t (not exported) and not just the
> dtrace_probedesc_t (exported).
>
> Maybe you should look at whether using the dt_probe_f callback variant in this
> case would benefit the rest of the code?  E.g. you don't need to do a provider
> lookup (by name) since there is a pointer to the provider in dt_probe_t.

That seems to be a different issue from the one in this patch. Finding a 
use for dt_probe_f should presumably have been done before dt_probe_f 
was ever introduced -- namely, d9590b9f17c1 "Introduce internal 
dt_probe_iter() function".  That commit introduced all this 
dtrace_probe_iter/dt_probe_iter complexity saying it was needed, but 
AFAICT dt_probe_f is still not used anywhere.  That patch was supposed 
to have been in support of the probe cleanup mechanism, but that 
mechanism does not use probe_iter.

I'm okay throwing out both the proposed patch and d9590b9f.

>> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
>> ---
>>   libdtrace/dt_probe.c | 10 +++++-----
>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/libdtrace/dt_probe.c b/libdtrace/dt_probe.c
>> index b6c79354..7fa6c341 100644
>> --- a/libdtrace/dt_probe.c
>> +++ b/libdtrace/dt_probe.c
>> @@ -989,14 +989,14 @@ dt_probe_info(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp,
>>   	pd.id = DTRACE_IDNONE;
>>   
>>   	/*
>> -	 * Call dtrace_probe_iter() to find matching probes.  Our
>> +	 * Call dt_probe_iter() to find matching probes.  Our
>>   	 * dt_probe_desc() callback will produce the following results:
>>   	 *
>> -	 * m < 0 dtrace_probe_iter() found zero matches (or failed).
>> -	 * m > 0 dtrace_probe_iter() found more than one match.
>> -	 * m = 0 dtrace_probe_iter() found exactly one match.
>> +	 * m < 0 dt_probe_iter() found zero matches (or failed).
>> +	 * m > 0 dt_probe_iter() found more than one match.
>> +	 * m = 0 dt_probe_iter() found exactly one match.
>>   	 */
>> -	if ((m = dtrace_probe_iter(dtp, pdp, dt_probe_desc, &pd)) < 0)
>> +	if ((m = dt_probe_iter(dtp, pdp, NULL, dt_probe_desc, &pd)) < 0)
>>   		return NULL; /* dt_errno is set for us */
>>   
>>   	if ((pvp = dt_provider_lookup(dtp, pd.prv)) == NULL)
>> -- 
>> 2.18.2
>>
>>
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