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

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Message-ID: <cc1e7d3d-32ad-693f-6db6-4573ad49cb20@linux.intel.com>
Date:   Wed, 22 Jul 2020 15:45:43 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 05/15] perf evlist: implement control command handling
 functions


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@...ux.intel.com>
>>> Acked-by: Jiri Olsa <jolsa@...hat.com>
>>> Acked-by: Namhyung Kim <namhyung@...nel.org>
>>
>> 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