[lttng-dev] Reading CTF trace using Babeltrace API

[jeremie.galarneau@efficios.com (Jérémie Galarneau)]

On Wed, Oct 23, 2013 at 10:50 AM, Salman Rafiq
<salman.rafiq at esk.fraunhofer.de> wrote:
> Hello again :)
>
> While reading Kernel trace events (system calls), I came across an issue related to reading the field 'args' inside 'sys_unknown' system call event.
>
> Below is the information I get using public babeltrace API's for the event field type.
> Ctf_type_id = 8  (CTF_TYPE_ARRAY)
>
>
> But when I try to read the value for the field using the following API
> char * bt_ctf_get_char_array(const struct bt_definition *field);
>
> I receive null value. Also it gives me warning that I am instead extracting a String.
> [warning] Extracting String
>
> Also, I am unable to read the value using the following API.
> char *bt_ctf_get_string(const struct bt_definition *field);
>

You should be using the bt_ctf_get_index() function to access the
individual elements of _args. Let me know how that works out.

As for the "Extracting string" message, it can indeed be misleading...

J?r?mie

>
> below is the sample event recorded:
> [00002934900435406801] (+0.000009630) sys_unknown: { cpu_id = 3 }, { id = 277, args = [ [0] = 22, [1] = 0, [2] = 4096, [3] = 2, [4] = 4096, [5] = 5 ] }
>
> AND the event definition:
> event {
>         name = sys_unknown;
>         id = 2;
>         stream_id = 0;
>         fields := struct {
>                 integer { size = 32; align = 8; signed = 0; encoding = none; base = 10; } _id
>                 integer { size = 64; align = 8; signed = 0; encoding = none; base = 10; } _args[6];
>         };
> };
>
>
> Any suggestion related to that will be very helpful.
> Thanks!
>
> Best Regards,
> Salman
> --
> Salman Rafiq
> Gesch?ftsfeld Industrial Communication
> Fraunhofer-Institut  f?r Eingebettete Systeme und Kommunikationstechnik ESK
>
> Hansastra?e 32 | 80686 M?nchen
> Telefon, Fax:  +49 89 547088-356 | +49 89 547088-221
> E-Mail:   salman.rafiq at esk.fraunhofer.de
>
> Internet:
> http://www.esk.fraunhofer.de
> http://www.twitter.com/FraunhoferESK
>
>
> -----Original Message-----
> From: jeremie.galarneau@gmail.com [mailto:jeremie.galarneau@gmail.com] On Behalf Of J?r?mie Galarneau
> Sent: Mittwoch, 9. Oktober 2013 01:50
> To: Mathieu Desnoyers
> Cc: Salman Rafiq; Julien Desfossez; lttng-dev at lists.lttng.org
> Subject: Re: Reading CTF trace using Babeltrace API
>
> On Tue, Oct 8, 2013 at 7:14 PM, Mathieu Desnoyers <mathieu.desnoyers at efficios.com> wrote:
>> ----- Original Message -----
>>> From: "J?r?mie Galarneau" <jeremie.galarneau@efficios.com>
>>> To: "Salman Rafiq" <salman.rafiq at esk.fraunhofer.de>
>>> Cc: jdesfossez at efficios.com, lttng-dev at lists.lttng.org, "Mathieu
>>> Desnoyers" <mathieu.desnoyers at efficios.com>
>>> Sent: Tuesday, October 8, 2013 2:52:38 PM
>>> Subject: Re: Reading CTF trace using Babeltrace API
>> [...]
>>>
>>> The problem is that the "id" fields in both struct
>>> event_header_compact and event_header_large acts as a variant's tag
>>> enumeration.
>>>
>>> For instance, if we take a look at the event_header_compact
>>> structure,
>>>
>>> struct event_header_compact {
>>>         enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
>>>         variant <id> {
>>>                 struct {
>>>                         uint27_clock_monotonic_t timestamp;
>>>                 } compact;
>>>                 struct {
>>>                         uint32_t id;
>>>                         uint64_clock_monotonic_t timestamp;
>>>                 } extended;
>>>         } v;
>>> } align(8);
>>>
>>> The "enum id" field will indicate the event's id if it has a value of
>>> [0, 30]. It also indicates that the "compact" structure is selected
>>> in the variant that follows. If id == 31, the "extended" structure is
>>> selected, which means that you should retrieve the "id" field's value
>>> from that structure.
>>>
>>> Since code is worth a thousand words, here's a more complete code
>>> sample to read the id fields.
>>>
>>> while ((ctf_event = bt_ctf_iter_read_event(iter))) {
>>>         uint64_t event_id = 0;
>>>         const struct bt_definition *stream_event_header_scope =
>>>                 bt_ctf_get_top_level_scope(
>>>                         ctf_event, BT_STREAM_EVENT_HEADER);
>>>         const struct bt_definition *id_definition =
>>>                 bt_ctf_get_field(ctf_event, stream_event_header_scope,
>>>                                  "id");
>>>         const struct bt_definition *v_definition =
>>>                 bt_ctf_get_field(ctf_event, stream_event_header_scope,
>>>                                  "v");
>>>
>>>         /* "id may be an enum, get the underlying integer if it's the case */
>>>         if (id_definition &&
>>> bt_ctf_field_type(bt_ctf_get_decl_from_def(id_definition)) ==
>>> CTF_TYPE_ENUM) {
>>>                 id_definition = bt_ctf_get_enum_int(id_definition);
>>>         }
>>>
>>>         /* Check if there is a "v" field and if it contains an "id" field */
>>>         if (v_definition &&
>>> bt_ctf_field_type(bt_ctf_get_decl_from_def(v_definition)) ==
>>> CTF_TYPE_STRUCT) {
>>>                 struct bt_definition const * const *list = NULL;
>>>                 unsigned int count = 0;
>>>                 unsigned int i;
>>>
>>>                 ret = bt_ctf_get_field_list(ctf_event, v_definition,
>>> &list, &count);
>>>                 if (ret) {
>>>                         goto end;
>>>                 }
>>>
>>>                 for (i = 0; i < count; i++) {
>>>                         const char *name =
>>> bt_ctf_field_name(list[i]);
>>>
>>>                         if (strcmp("id", name) == 0) {
>>>                                 id_definition = list[i];
>>>                                 break;
>>>                         }
>>>                 }
>>
>> Instead of doing this bt_ctf_get_field_list() and iteration, can't we simply use bt_ctf_get_field() to try getting the struct bt_definition ?
>
> Right. I was under the impression the bt_ctf_get_field() would only work on scopes, but it's not the case.
>
> Thanks!
> J?r?mie
>
>>
>> Thanks,
>>
>> Mathieu
>>
>>>         }
>>>
>>>         if (id_definition &&
>>> bt_ctf_field_type(bt_ctf_get_decl_from_def(id_definition)) ==
>>> CTF_TYPE_INTEGER) {
>>>                 event_id = bt_ctf_get_uint64(id_definition);
>>>         }
>>>
>>>         printf("id = %" PRIu64 "\n", event_id); }
>>>
>>> Regards,
>>> J?r?mie
>>>
>>> > Thanks a lot!
>>> >
>>> > Regards,
>>> > Salman
>>> >
>>> > --
>>> > Salman Rafiq
>>> > Gesch?ftsfeld Industrial Communication Fraunhofer-Institut  f?r
>>> > Eingebettete Systeme und Kommunikationstechnik ESK
>>> >
>>> > Hansastra?e 32 | 80686 M?nchen
>>> > Telefon, Fax:  +49 89 547088-356 | +49 89 547088-221
>>> > E-Mail:   salman.rafiq at esk.fraunhofer.de
>>> >
>>> > Internet:
>>> > http://www.esk.fraunhofer.de
>>> > http://www.twitter.com/FraunhoferESK
>>> >
>>> >
>>> > -----Original Message-----
>>> > From: jeremie.galarneau@gmail.com
>>> > [mailto:jeremie.galarneau at gmail.com] On Behalf Of J?r?mie Galarneau
>>> > Sent: Mittwoch, 2. Oktober 2013 20:25
>>> > To: Salman Rafiq
>>> > Cc: jdesfossez at efficios.com; lttng-dev at lists.lttng.org; Mathieu
>>> > Desnoyers
>>> > Subject: Re: Reading CTF trace using Babeltrace API
>>> >
>>> > On Wed, Oct 2, 2013 at 12:55 PM, Salman Rafiq
>>> > <salman.rafiq at esk.fraunhofer.de> wrote:
>>> >> Dear LTTngers,
>>> >>
>>> >> I would like to ask few questions related to the API's for reading
>>> >> CTF traces.
>>> >>
>>> >> 1.  Is there any way to read CTF metadata independently, like we
>>> >> have certain API's to read the events.
>>> >>
>>> >
>>> > Not from the public API, unfortunately.
>>> >
>>> >> 2. There are certain scopes defined in ctf/events.h like:
>>> >>         BT_TRACE_PACKET_HEADER          = 0,
>>> >>         BT_STREAM_PACKET_CONTEXT        = 1,
>>> >>         BT_STREAM_EVENT_HEADER          = 2,
>>> >>         BT_STREAM_EVENT_CONTEXT         = 3,
>>> >>         BT_EVENT_CONTEXT                = 4,
>>> >>         BT_EVENT_FIELDS                 = 5,
>>> >>
>>> >> I could not figure out the way to ready the fields 'id' and
>>> >> 'stream_id', for a particular event while iterating through the trace.
>>> >> Though I can ready the event name using an API and fields using
>>> >> BT_EVENT_FIELDS as a scope.
>>> >> For e.g. consider the
>>> >>
>>> >> event {
>>> >>         name = sched_migrate_task;
>>> >>         id = 1;
>>> >>         stream_id = 0;
>>> >>         fields := struct {
>>> >>                 integer { size = 8; align = 8; signed = 1; encoding =
>>> >>                 UTF8; base = 10; } _comm[16];
>>> >>                 integer { size = 32; align = 8; signed = 1; encoding =
>>> >>                 none; base = 10; } _tid;
>>> >>                 integer { size = 32; align = 8; signed = 1; encoding =
>>> >>                 none; base = 10; } _prio;
>>> >>                 integer { size = 32; align = 8; signed = 1; encoding =
>>> >>                 none; base = 10; } _orig_cpu;
>>> >>                 integer { size = 32; align = 8; signed = 1; encoding =
>>> >>                 none; base = 10; } _dest_cpu;
>>> >>         };
>>> >> };
>>> >>
>>> >
>>> > The "id" field is part of the BT_STREAM_EVENT_HEADER scope, while
>>> > the "stream_id" field is part of the BT_TRACE_PACKET_HEADER scope.
>>> >
>>> > The code below is adapted from converter/babeltrace.c's
>>> > convert_trace() loop to print both values.
>>> >
>>> > while ((ctf_event = bt_ctf_iter_read_event(iter))) {
>>> >
>>> >         const struct bt_definition *stream_event_header_scope =
>>> >                 bt_ctf_get_top_level_scope(
>>> >                         ctf_event, BT_STREAM_EVENT_HEADER);
>>> >         const struct bt_definition *id_field =
>>> >                 bt_ctf_get_field(
>>> >                         ctf_event, stream_event_header_scope,
>>> > "id");
>>> >
>>> >         printf("id = %" PRIu64 "\n", bt_ctf_get_uint64(id_field));
>>> >
>>> >         const struct bt_definition *packet_header_scope =
>>> >                 bt_ctf_get_top_level_scope(
>>> >                         ctf_event, BT_TRACE_PACKET_HEADER);
>>> >         const struct bt_definition *stream_id_field =
>>> >                 bt_ctf_get_field(
>>> >                         ctf_event, packet_header_scope,
>>> > "stream_id");
>>> >
>>> >         printf("stream_id = %" PRIu64 "\n", bt_ctf_get_uint64(
>>> >                        stream_id_field)); [...] }
>>> >
>>> > Regards,
>>> > J?r?mie
>>> >
>>> >>
>>> >> Any help or suggestion related to this issue will be really appreciated.
>>> >> Thanks!
>>> >>
>>> >> Regards,
>>> >> Salman
>>> >>
>>> >> --
>>> >> Salman Rafiq
>>> >> Gesch?ftsfeld Industrial Communication Fraunhofer-Institut  f?r
>>> >> Eingebettete Systeme und Kommunikationstechnik ESK
>>> >>
>>> >> Hansastra?e 32 | 80686 M?nchen
>>> >> Telefon, Fax:  +49 89 547088-356 | +49 89 547088-221
>>> >> E-Mail:   salman.rafiq at esk.fraunhofer.de
>>> >>
>>> >> Internet:
>>> >> http://www.esk.fraunhofer.de
>>> >> http://www.twitter.com/FraunhoferESK
>>> >>
>>> >
>>> >
>>> >
>>> > --
>>> > J?r?mie Galarneau
>>> > EfficiOS Inc.
>>> > http://www.efficios.com
>>>
>>>
>>>
>>> --
>>> J?r?mie Galarneau
>>> EfficiOS Inc.
>>> http://www.efficios.com
>>>
>>
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com
>
>
>
> --
> J?r?mie Galarneau
> EfficiOS Inc.
> http://www.efficios.com



-- 
J?r?mie Galarneau
EfficiOS Inc.
http://www.efficios.com