Re: [PATCH v12 05/15] perf evlist: implement control command handling functions

[Alexey Budankov]

On 22.07.2020 15:34, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jul 22, 2020 at 09:27:34AM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Fri, Jul 17, 2020 at 10:01:33AM +0300, Alexey Budankov escreveu:
>>>
>>> Implement functions of initialization, finalization and processing
>>> of control command messages coming from control file descriptors.
>>> Allocate control file descriptor as descriptor at struct pollfd
>>> object of evsel_list for atomic poll() operation.
>>>
>>> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
>>> Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
>>> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
>>
>> I'm applying locally for testing, but can you answer what is the reason
>> for that newline in the CMD_ACK_TAG? I tried looking at previous
>> discussion but couldn't quickly find any reasoning for that
>>
>> - Arnaldo
>>
>>> +++ b/tools/perf/util/evlist.h
>>> @@ -359,4 +359,22 @@ void perf_evlist__force_leader(struct evlist *evlist);
>>>  struct evsel *perf_evlist__reset_weak_group(struct evlist *evlist,
>>>  						 struct evsel *evsel,
>>>  						bool close);
>>> +#define EVLIST_CTL_CMD_ENABLE_TAG  "enable"
>>> +#define EVLIST_CTL_CMD_DISABLE_TAG "disable"
>>> +#define EVLIST_CTL_CMD_ACK_TAG     "ack\n"
>>
>> What for? That '\n'?
> 
> Oh, I see, this is not a _command_, it is a _response_, and the sender
> expects a newline, right?

Right. Shell commands can expect strings terminated by \n, e.g. 'read -u'.
See sample bash script in 00/15 for example.

> 
> So I think this needs to be marked clearly as:
> 
> // Commands accepted by 'perf record'
> 
> #define EVLIST_CTL_CMD_ENABLE_TAG  "enable"
> #define EVLIST_CTL_CMD_DISABLE_TAG "disable"
> 
> 
> // Responses sent by 'perf record'
> 
> #define EVLIST_CTL_RSP_ACK     "ack"
> 
> And then make the response add the newline, as conceivably we could have
> something like "nack", "invalid", "enoperm", etc, no?

That above makes sense.

> 
> Anyway, this can be done on top of this series, so I'm continuing
> processing it locally.
> 
> - Arnaldo
> 

Alexei