[lttng-dev] Reading CTF trace using Babeltrace API
Jérémie Galarneau
jeremie.galarneau at efficios.com
Tue Oct 8 19:50:21 EDT 2013
On Tue, Oct 8, 2013 at 7:14 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> ----- Original Message -----
>> From: "Jérémie Galarneau" <jeremie.galarneau at 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!
Jérémie
>
> 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,
>> Jérémie
>>
>> > Thanks a lot!
>> >
>> > Regards,
>> > Salman
>> >
>> > --
>> > Salman Rafiq
>> > Geschäftsfeld Industrial Communication
>> > Fraunhofer-Institut für Eingebettete Systeme und Kommunikationstechnik ESK
>> >
>> > Hansastraße 32 | 80686 München
>> > 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 at gmail.com [mailto:jeremie.galarneau at gmail.com] On
>> > Behalf Of Jérémie 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,
>> > Jérémie
>> >
>> >>
>> >> Any help or suggestion related to this issue will be really appreciated.
>> >> Thanks!
>> >>
>> >> Regards,
>> >> Salman
>> >>
>> >> --
>> >> Salman Rafiq
>> >> Geschäftsfeld Industrial Communication Fraunhofer-Institut für
>> >> Eingebettete Systeme und Kommunikationstechnik ESK
>> >>
>> >> Hansastraße 32 | 80686 München
>> >> 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
>> >>
>> >
>> >
>> >
>> > --
>> > Jérémie Galarneau
>> > EfficiOS Inc.
>> > http://www.efficios.com
>>
>>
>>
>> --
>> Jérémie Galarneau
>> EfficiOS Inc.
>> http://www.efficios.com
>>
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
--
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com
More information about the lttng-dev
mailing list